I know im asking randomly but does someone know of a tool to get back into an instagram account? I was stupid lost my account password. I appreciate any tricks you can offer me
LOL!! All the marketing hype in the cycling industry is actually entertaining once you break the code on it. Especially entertaining on group rides!! 😀😀
Very interesting video. Just to add some thoughts of someone who welds frames. From a weld up point of view (more so in ti, but also steel) dropping or raising the seat stays away from the top tube creates a number of alignment and distortion issues. Assuming a standard tack in place, dropped or raised stays will make twisting of the seat tube relative to the head tube likely, as well as there being a risk of seat tube being pulled slacker or steeper during full weld up. It can create stresses in the seat tube that make the tube want to rest in an S profile, which in turn will mean that seat post reaming will be unequal, thinning one face of the ID of the tube over the other. Titanium wants to move a lot in welding, and this sort of set up accerbates it. In a lot of ti bikes (and some steel) the top of the seat tube has a welded, thicker insert that allows a standard sized post to be used without shims, which wouldn't be practical with dropped stays, and finally it would be very hard to engage any sort of heat sink if the stays were dropped. All these issues can be resolved, but as this video very clearly breaks down, there isn't much point.
As someone who welds titanium bike frames on a daily basis, this comment has a value that, from a custom-build context, supersedes the aspect of comfort only. Also noteworthy that wall thickness in the seat tube and the type of seat tube/seat post interface (welded collar or insert) will play a huge role in the quality of the build as noted by Matthew.
But most dropped seatstay bikes are specifically designed that way and aspects like wall thickness/butting have certainly been considered/modeled/stress tested/engineered, at least more so than the average custom builder is capable of...right? How many round tubed dropped seatstay metal-framed bikes are out there anyway? When Paul built my Rock Lobster, he didn’t create a CAD model or put the final product in a stress test rig. I don’t think he even has my measurements anywhere except on a piece of paper.
@@kidsafe Yes, I would agree that most are designed for lowered stays (I would hope). The percentage is pretty small of round-tubed dropped seatstay metal-framed bikes out there. In my experience, as in many of custom builders, I would suspect that the request for this type of build is a much larger percentage than market average due to clients seeing this type of build (and marketing) on non-metal frames. In other words, I get asked all the time for this type of build. I built only one, many years ago, and decided to never build again for the exact reasons Matthew noted above. ps. You got a great bike:)
@@kidsafe Was only adding a bit of input purely from a steel/ti fabrication point of view, I don't have any real input or knowledge on the design or fab process of mass produced carbon frames. One note in regards to small builders and CAD. Up until recently this would have been true, but since Fusion was released, I have had access to (in the scheme of things) relatively basic but very functional FEA programme, which I can and do use as a sanity check/proof of concept etc... and know of other builders who use it in this way too. Most builders do not stress test their frames, obviously for one-off custom builds it would be financially unviable, but this is also because the basic design of, and materials used in metal construction have all been in use and proved to be incredibly safe and unlikely to fail in their intended uses. This is of course only from a design and materials sense. These bikes can still fail, but it will be due to manufacturing faults, user error etc rather than flawed tubing choice or frame geometry.
@@crisptitanium I was wondering if any of the tubes was dented, say with a crease type of dent, and actually it happened on the seat stay of a Independent Fabrications steel frame I have, and your end user wanted to restore the original strength, would you recommend silver braze fill, small welded patch or total replacement? I cannot find the tube material.(20 years old)
I was skeptical because being an engineer as well I always imagined it would have at least a small (if insignificant) improvement in deflection. Seeing the simulations really clears it up, thanks! This and other people's videos about frame comfort make me realise I should really only choose my frame material based on durability and things like galvanic corrosion being a problem or not. (That's mostly why I'll stick to steel) I'm already a huge fan of supple tyres for comfort, but now I guess I should also start looking for a seatpost with good dampening characteristics ;)
You and Hambini are like the Tiff Needell and Jeremy Clarkson of bike engineering (in the) world on youtube. We need a bike build challenge for the both of you and one of Stig's cycling cousins to test them - who could that be? Could be something for Jeffers to do between whatever bans he'll be serving in the future.
@@PeakTorque haha yeah we need someone that can't hide behind a lamp post, just out of interest what height and weight etc are you, you look like you could lay down a watt or 2.
Exactly. Tiff Needell and Chris Harris would be a better comparison given the information presented. Though the way Hambini presents stuff is Clarkson-esque.
In your analysis, the bump load is a static load, but I would be interested to hear your thoughts about how well this approximates the spectral nature of road vibrations. It is close for the response for big low frequency hits, but not necessarily for higher frequency vibrations. There will be a difference between the compliance of the structure with a static load vs the transmissibility of random vibrational input from the base to the seat, but that will depend on the bike system modes vs the road vibrational inputs, which I have no idea what they would be. Anyways, thanks for your thoughtful videos, I look forward to the next one.
Hi mate nice video but I think you may have over looked a key point which may be worth investigating: If a 2000N load is applied relative to the saddle then a corresponding load will also be applied to the drop outs (via the wheels) in the opposite direction. Therefore it is likely that dropped seat stays will also allow the chain stays to flex more along their length, due to the reduced vertical bracing angle. This is likely to reduce the rate of force transfer from dropouts into the frame. I believe this is the bigger aim of dropped seat stays, I look forward to hearing your opinion on this. For example of this idea please look at the Cannondale scalpel’s pivot-less rear suspension.
Not just crack'n'fails either . Salsa el kaboing used a chainstay flex to preload the rear shock by 30mm for the rear linkage moved . Sunn also made a pivotless soft tail that didn't have a dampener.
@@PeakTorque No doubt the seat post is by far the biggest factor but I think the combination of seat tube and chain stay deflection could potentially move the design feature from markings BS, to the realms of plausibly effective. In my opinion the best design so far is trek’s newest madone/domane isospeed: 100% decoupled seat post and ‘mast’ with a bushing pivot and an adjustable carbon leaf spring running under the top tube. This design allows the stiffest double diamond shape and good comfort but definitely adds weight.
Definitely agree on the stiffness claims...that said, any potential aero gains isn't ALL about frontal area reduction, but in improvements in drag coefficient. Even a completely round seat stay cross-section becomes "longer", and more ovalized (and thus lower Cd) when it is "dropped" more horizontal. If the seatstay is actually an aero cross-section, then dropping the stay makes it's cross-section a longer airfoil, which is going to be lower Cd.
Just by looking at the two models in the simulation I'd have made a guess that the dropped seatstays prevent the seat tube from moving freely in the opposite direction to the seat post, thus even making the frame more rigid. This channel is a breath of fresh air to counterbalance the stench that mainstream cycling platforms churn out for sales.... Keep at the great work!
Whether they add to comfort or not, I find traditional seatstays much more visually appealing than drop seatstays. To Me, the perfect rear end in a bike would be of Salsa WarBird's (2019 and newer), followed by the Specialized Aethos', Giant TCR's and Cannondale Synapse (2018 or thereabouts and newer). I also suspect (irrespective of my visual compromise of dropped seatstays) that dropped seatstay frames are more fragile than non-dropped designs.
Spot on about weld fatigue. I had a MTB with dropped stays, the suspension pivot was mounted halfway between the BB and top tube-seat tube joint. I cracked the TT-ST weld 3 times before the 4th warranty frame had a custom gusset to reinforce it. Devinci moonracer frame in a large size, with plenty of seatpost length, and good insertion.
I have a aluminum gravel bike. It was very stiff and uncomfortable to ride. I swapped out the aluminum seat post with a carbon seat post and It made it a very comfortable bike for the long rides.
Thanks I was wondering about this. I have two aluminum commuter bikes. I put a suspension seat post on the boardman but the cannondale SAVE is noticeable in its comfort in comparison but will put a carbon seatpost on it at some point to make it more comfortable.
@@smallhatshatethetruth7933 I had bought a round seat post that was curved back. I took a chance of buying a chinese one. So far very happy with it. It does stick out quite a bit though. I think it's been 3 years ago when I put it on. Cheap, Cheap.
I had also had put Pirellis on my aluminum areo road bike. The carbon seat post was a true air foil shape it flexed side ways better than back wards. The wheels made it so much better than I had expected.
If dropped seat stays means lower peak load on the seat stay to seat post junction then for carbon that could be a huge advantage making the frame less stiff there which may impact ride quality
Thanks for the analysis and video. As a structural engineer, I've been wondering about the claim of dropped seat stay providing more comfort. It simply doesn’t make sense, unless the top tube also drops down. I really think the real reason for dropped seat stay is to reduced weight by using shorter tubes, which is a huge selling point in this weight concious industry. The seat stay tubes are compression mbers, and the failure mode is buckling, so the shorter unbraced length also increases buckling strength, perhaps resulting in thinner walls. In addition it provides a secondary brace point for the down tube. Perhaps this allows for a lighter down tube as well. It seems to me the stiffest rear triangle is a 60-60-60 triangle. So when you drop the seat stay, you probably don't want to drop it below 60 degrees from he chain stay.
You didn't mention flattened tubes, which I imagine flex a lot more. Riding a Topstone Carbon I can say that with almost horizontal seatstays you can feel a lot of flex.
Another disadvantage of dropped seat stays is that it will obstruct your view of the cassette when riding making it much harder to see what gear you are on
We shouldn't question big corporations bullshit, they don't want to make as much money as they can on us, by selling us cheap hyped up shitty products! Great video my friend!
dropped seat stays can increase comfort because it allows for a removing the back section of the top part of the seat tube. it increases the cantilever length of the seat post and therefore its deflection aka comfort. e.g. look at the Rose backroad or Rose reveal. It is basically the same effect that canyon tried to do with the seat post design of the aeroad.
The point about lack of fatigue testing on custom frames is interesting. I bought a custom Enigma Ti frame years ago, and after a couple of years it cracked at the head tube. They honoured the warranty and sent me a new one which was a couple of hundred grams heavier. So you could argue that the customer is doing the fatigue testing!
I'm no engineer and only have the most peripheral knowledge on these subjects but I intuitively felt that (if anything) the junction of the top tube and seat post would have the greatest effect on seatpost deflection. By decoupling the truss structure I imagined you simply leaft a greater tension force on the top tube/seat post junction/welding to manage but didn't improve "dampening". Thank you for all your videos and giving me language for concepts I couldn't put words to. 👊👊
I have the Litespeed T5 lifted seat stays with a Ti set back seat post. I like that after a long ride on crappy roads in my area I don't feel all beat up. The frame feels springy especially on climbs, but in a good way. There is no doubt a carbon version would be stiffer and transfer power better, but I don't race and look for comfort over efficiency.
Nice peek into the topic! I hope for the future video you will plot frequency responce spectres and include second in-plane case: 100kg force on the saddle, sinusoidal vertical displacement of what are currently the fixtures (at postresonance frequencies, of course) Would be also nice not to wait for as long as with the crank lenght followup, but who we are to judge...
Great video. But surely the forks and seat stays can and are designed to act a suspension units. This video proves that the front main triangle stiffness is not effected by the seat stay design and the seat post is the main factor. But does not prove if the rear triangle design effects comfort. Cannondale and Specialised have for example produced designs that have been more forgiving due to the rear triangle design. Many Alloy bikes do this. If you model the front triangle as fixed and the load applied to the rear axle. Then surely you can isolate the effect of rear triangle and visualise the effect of different designs including different cross sections of the top stay tube.
I'm not an engineer, but i would assume there's a energy transfer when the rear wheel lifts up from hitting a bump. Having the seat stays lower could potentially shift said energy more laterarly instead of vertically. In other words, perceived shock of hitting a bump could be transferred to the seat post instead of traveling up into the seat itself. Mitigation or cushioning of the Primary shock wave vs secondary. Another way to think about it is the difference between hitting upward on the seat post vs hitting the side of the seat post. Yes there's a transfer of energy either way. However, there is a directional component to energy transfer and felt energy. 🤷🏻♂️
@Peak Torque, I dunno, I feel like you're missing something with your boundary conditions at the drop outs. Say for example the cyclist rides off a curb, the rear wheel will impact the ground and this impulse would be transmitted through the rear triangle . I recognize that the difference in frame deflection is minimal between each case; however, I feel like (*an engineers three favorite words*) the reduced MOI of the rear triangle should be significant enough to offer a lower effective spring constant and thus absorb more of the impulse. I'm no expert in FEA but is there a way to simulate the case mentioned and provide an effective spring constant for the rear triangle of a conventional vs. dropped seat stay?
What about a cluster like the Lapierre Xelius? The top tube connects to the seat post but the seat stays do not. The seat stays shoot past the seat post and connect only to the top tube mid span. This connection may be less stiff then a traditional one but in the end it’s still a frame with the same support conditions at the dropouts so it’s probably very similar. The cantilever seat post and tires will almost always provide the bulk of the deflection as they are the softest spring.
Disagree ,Your FEA are maybe wrong, seat stay can deformed in differents planes, I sized bike in the industry , it has been validated that it is more compliant. I usually agreed with you , i like your channel, but this one you will have to re- evaluate
I just started watching your stuff. It’s very good and we are aligned in many ways. I’ve always told people that the seatpost has the most impact in ride quality. I will share this with people from now on. You mentioned speed wobble. Have you ever done a video on this topic? Would you consider Doing a video on this topic?
I'd also like to add that a combination of 11-17º top tube slope and seatstays that continue from the top tube base will not only look infinitely better, but also yield the same or greater compliance as a combination of a [near-]horizontal top tube and dropped seatstays. As yet another bonus, it will be less delicate than dropped seatstay frames. A lot of advantages (including a visual appeal) - and not a single disadvantage for sloping top tube & normal stay design.
this is the third video from your newly discovered channel i am watching in a row (subscription right on the first one) - other two being about why those cranks fail and stiffnes of hubs clamping. few more tabs i just opened to be watched after this one. if i was gay, i'd hope you are and propose to you. wow! conclusive, logical, reasonable, plausible. my bikes were made between 1960 and 1999, thus your topics don't even cover my own fleet, yet i am soooo curious into your engineering knowledge. thank you!!! i love you.
Going by this logic, wouldn't Giant's (and others) compact geometry be slightly more comfortable as there is usually a greater distance from top tube to seat, giving more flex in the seat post?
So riding a small frame with a lot of exposed seatpost and 28mm or larger tubeless tires is the most comfortable option. Bonus point is, that you can use the stiffest frame there is since it makes so little difference.
I know this has no engineering criteria, but i hate the look of dropped seat stays. 🤔😆 Just as a side note, the rear end of the triangle has changed considerably with the introduction of disc brakes, wider hubs and wider tyres. I do believe this design change is more about accommodating these design changes. It is a smaller triangle with thicker seat stays to accommodate the lower angle. This would make the triangle more rigid. Something to consider maybe?
Might be a different equation for a carbon fibre lay up - less stiff seat and top tube with stiffer down tube, chain and seat stays. By dropping the seat stays you then allow the greater flex in the seat and top tubes to operate? If that is accepted then the dropped seat stays on the alloy version of the bike may be more about matching the aesthetics of the better performing carbon frame.
It's not as if the strength of the seat tube is compromised in tension at that point except of course the bottle bosses. But in reality I wouldn't think you would be getting anywhere near the yield strength of any frame material.
What jumps out to me is that the model of the dropped seat stays shows the head tube anglular deflection occurring which could mess up braking or steering control (see 7:30). Dropping the seat stays introduces a needless pivot fulcrum.
"Even your choice of bib shorts and chamois has more deflection than the frame". Brilliant. Now I need more vertically compliant chamois. What a great new marketing tool for cycling clothing manufacturers.
They’ll be a new generation of endurance compliance saddles soon probably like the old selle Italia turbo or may be a modern saddle with a deeper saddle rail.
This was super interesting, could you model a triple triangle design to see how the same area would behave under load?. Or even if the triple triangle is even as groundbreaking as the marketing claims make the technology out to be?
I like your engineering analysis of bike tech, but I feel like this one is missing something. You assume "comfort" only for a seated rider. The saddle is only 1 of the contact points for the rider. You ignore handlebars and more importantly the pedals, and don't account for a rider that isn't seated. If you consider a gravel bike on a bumpy descent where the rider is standing, or a roadie in a supertuck that smacks into a pothole, the seatpost deflection has no affect and it is the rear triangle that has to absorb energy before it is transmitted to the rider via the pedals. I'd love to see this same test done where the stress is done from the rear dropout.
Very enjoyable! I’d be interested in your thoughts on designs where the seat stays are not fixed to the seat tube - thinking here of the Trek IsoSpeed design, and the linkage on the Cannondale Topstone. Also, as a very light rider, who rides without layback (seat pretty far forward), I always am thinking that any supposed compliance is going to be even less, given that I won’t be acting as as big a lever as a heavy rider with large layback.
I was thinking about the Cannondale as well. Although the pivot point allows a rotation between the seat stays and the seat tube, I suppose that the actual effect (a higher translation in the z direction in order to increase comfort) is mostly depending on the stiffness of the seat tube and seat stays. When both are stiff as hell, then the pivot is useless. idk
If you're referring to the GT "triple triangle" design - the increase in vertical compliance is going to be even more negligible than what was shown here. Back in the 1980s when tubing diameters were considerably smaller than current designs the "triple triangle" increased the rigidity of the seat stay, seat tube and top tube as well increasing the strength of the whole area. In the past quarter century the bike industry has gone away from lugged steel and small diameter tubing thus negating the design positives. A standard double diamond bike frame design is more efficient (slightly). Another negative for "triple triangle" type frames is the considerably greater Heat Affected Zone (H.A.Z.). The reason for butted tubes used in bike frames is to counteract the tubing being weakened during welding/brazing. A greater H.A.Z. requires a longer area of the tube(s).
You have been mistaken, in both instances the peak stresses are lower for the dropped seat stays. You have made my mind. Think about it, the double diamond frame would be the strongest if both triangles were equilateral. The dropped seat stay frame looks closer to an Isosceles' triangle distributing the load equally across the seat post welds. The peak weld stresses illustrate this perfectly, normal seatstays have weaker seatstay welds.
On aero bikes I have noticed a much stiffer ride. Sme of this might be tyre (higher pressure) but from the video series I am going to guess a huge part of that is the seat post shape. So if ''compliance' is an issue on aero bikes, then surely going back to a round seatpost while keeping all the other members aero shaped would be a happy medium?
@Peak Torque... You proved that dropping the seat stays actually does provide more lateral deflection at the seat thus providing some marginal suspension. (Some is better than none, correct?) 7:52
Dropped seat stays combined with a compact frame (aggressive sloping top tube) result in a longer seat post with more flex/deflection = more comfort. Of course, high gains in comfort result with lower bodyweight i.e. sub 12% bodyfat. However, bike manufacturers cannot lever sales out of that factoid.
It is right if the the force comes from the saddle, like in the video. BUT Look at the force point in the Center of the rear hub. Look at the vertical tension and flex, you Look only on the horizontal from the saddle.
I'd like to suggest a tweak in your modeling that may dramatically change your conclusion(?) Argument "for" I've always *assumed* that (to increase flex) for the droped seat stay to be effective it must be *combined* with a "thinned" seat post croass section (ostensibly for tire clearance). (Assumption) The point of low area moment (the "flatest" cross section on the seat post in front of the rear tire) creates an opportunity for the designer to tune in the flex amount AND rhe seat arc they're seeking (for the seat total system (=> increased repeatability of flex/ride between different riders). The design enables a engineers to control net Flex much more precisely. Controlling the flex Pivot Point ( down near the bottom bracket). => dramatically changing the Arc of the seat (effective arc length 2.5x ro 4x?). It will mitigate the seatpost height and frame seatpost overlap effects that dramatically change Flex/"ride" between riders (w/different leg lengths on the same frame size). As handlebar width is adapts (to shoulder width) as frame size increases, this "hinge" can adapt as riders weights increases (w/larger frames) use slightly different seatpost extensions. Seat posts would fine-tuned ride versus be the primary device.
Surely the dropped seat stays would increase potential deflection in the y-axis, ie left-right. After all, the load on the bike is going to be alternating from left to right as the rider is pedaling, so dropping the seat stays, which hold the seat tube rigid, would allow lateral flex. Obviously fore-aft and vertical flex are still restrained by the top tube, so any change in deflection there will be minimal, unless you go for the full-on MTB compact geometry, and elongate the seatpost. But lateral compliance will still occur as the rider applies a downward lid to the bottom bracket on each alternating pedal stroke. I say this as someone perfectly happy with my traditional diamond frame bikes, but I think there’s more to the dropped stay design than your analysis is showing. As others have said, allowing for flattened stays should also figure into the analysis; I can definitely feel more grip in the rear wheel of my CAAD10 than in other similar bikes with round stays.
Where is the frame constrained? Is it at the dropout and head tube(fork) only? Is the bottom bracket shell constrained? I would have expected the bottom bracket to move down very slightly under compression, and the seat stay to really push into the seat tube. While a metal bike with dropped seat stays shouldn't have much more deflection, I would assume that combined with varying of carbon layup, the dropped stay would allow for quite a bit more bowing of the seat tube.
@@PeakTorque You should probably model the rear dropouts, some sort of fork, and hubs. Get rid of the fixed constraints if you really want to examine the difference.
I’d be interested to see how sloping the top tube effects your model. Giant have been sloping the top tube for years. Personally I prefer the appearance of a flat top tube but I suspect it’s less comfortable.
I agree it's in the seat post, but what you have missed out is that the comfort or compliance really also depends on the foreaft of the saddle placement due weight
As someone with a custom steel frame and similar body measurements, it would be interesting to look at the top tube angle as it modulates the flex. Mine is a 6 degree slope, which is for whatever reason considered a standard (10 years ago when it was made). But as you're thinking of building one up, it'd be an interesting exercise.
When I was younger, I don't remember anyone ever discussing comfort with regard to bicycles... unless they were balloon tired cruisers, or some kind of bike aimed at senior citizens. They're supposed to beat you up a bit.... no? 🤣
The dropped SS appear to normalize the weld stresses for the two points you looked at. That would appear to point to dropped seat stays as a better overall design. Not for comfort, but for long term weld durability. But I’m wondering where else the stress may have increased. Normally trade offs aren’t free.
I prefer the traditional look of the seat stays reaching the top tube, and in my limited knowledge I thought a shorter tube would be stiffer than a longer one. I own two Lynskey's one Helix pro and a 460 and both are stiff enough to race on and I am 6ft 5in and 190lbs.
I'm No engineer. I can See Yor Frame model flexing. Where is your model fixed: - Bottom bracket ? ( It Looks Like that ) Or - lowest Point of the headtube and both Rear dropouts? ( AS whilst Riding the load would be hold there. The Bottom Bracket should have at least SOME groung Clearance 😅. ) Reason for the question: the Quite Low seatstays of the Cannondale Topstone. Those Stays act Like a pushrod to Bend the seattube. Add to that a flexing Point in the rear Part of the toptube and voila: Suspension! Or am i Missing a vital Point Here?
But what about deflection up in the chain stays. Does the drop seat stays effect that? Like the way Moots YBB micro suspension uses chain stay deflection as a suspension.
Ya, can the dropped seat stay itself bend? Resulting in more comfort as the angle of attack of the bumps might be different comparing to a higher seat stay? I noticed my Caad13 dropped seat stay looks quite low so it could bend in itself as the bumps are hitting it upwards?
There will be chain stay deflection but you'll notice that Moots have used small diameter chainstays to allow the YBB seatstay up to 20mm of travel. Many chainstays in Ti builds these days use at least 1" diameter tubes and 0.9mm wall thickness which is noticebly stiffer when compared to my old 94' Serotta Legend (
Hi, Thanks for the informative video and the modeling. I think that your model may have given a result associated with the material choice and not the frame layout. As you probably know, Aluminum is more flexible than Titanium by nature. Young modulus for Aluminium is 70 GPA, whereas Titanium is 120 GPA. I think that for your model, you should change the material choice to be either Titanium or Aluminium for the frame and Seatpost, that way it would give a better output for the frame design only. Thanks
Physics will not be denied 😁. Aerodynamics or no aerodynamics, a tube attachment not at a node has every structural engineer ever turning in their graves. It's a testament to the fatigue properties of catbon composites that such crimes go unpunished.
I think the aero gain of dropped stay is less of the reduced frontal area, but more from better shape. Consider round tube, angle it a bit and cut horizontally, you get an oval-ish shape. angle it even more (dropped stay) and it become even more oval with longer cord length.
True. But at this Reynolds and Dimitriev that chord length is so small its smaller than all the local vortices, so it probably won't make a difference.
Now I'm worried about the significantly higher and more localized stress at the SS-ST weld. How come it is so much more stressed than the dropped seat stay. I would have expected the exact opposite case. It could become the main reason to adopt the dropped seat stays.
Now thats a surprisingly predictable result - thanks for the analysis, great work👍 Now try the effects of using smaller diameter seat stays and different wall thicknesses. The results may surprise you... Cheers
Hmm. Interesting, but I don't think this really addresses the main claim wrt compliance, which is that dropped stays decrease so called 'buzz' or 'chatter', i.e. high frequency noise rather than visible bumps in the road. Some implementations do have actual suspension elements built in so I think your question would be more suited to those specific builds. As you say, your model is very simple and side steps looking at an actual frame from a manufacturer in conjunction with their specific claims. Can see why you might want to avoid doing this though.
Nice ! Its all the same for " aluminium ", " steel or stainless steel " and " carbon fibers " frames ? Idea for a next video Myths and reality about Integrated Seat Posts ( both in metal be it steel, ti or carbon isp ) . They are mainly gone from nearly all productions bikes. But some small and not so small custom builds are using them. Mainly for anesthetics I guess. They also reduce practicability for travel etc. But speedvagen for example make some bolds unproven statements about them. Thanks Have a good one
You good sir should sell those frames on the mass market. It's so damn hard to get high stack/short reach frames, and who wants to get a current Domane/Roubaix/*Insert a Truck's Name* anyway ?
Not an engineer but just looking at what you have modeled it looks like you are only thinking about how the whole system reacts to a person just slamming their butt downward on to the seat at a standstill. In terms of what actually happens when you ride the bike out on the road you have to consider the force of the tire hitting a pot hole and that force being send upward (not completely from top to bottom but at some angle like 11 o'clock) this would depend on the impact but something like that should send an upward force starting at tire - rim - spokes - axle - rear dropout - frame tubes - seat post - seat - then finally your butt and then the rest of your body ending with your hands. So a force then coming into the rear dropout upward and slightly back is going to flex the bottom stay where it rotates a little around the bb, but the topstays would be pushed upward where if not put into a hard intersection like a traditional bike that has a top tube right there it could instead flex the seat tube a little and not send most of the impact into the seatpost and cause more bending there. Either way thanks for the vids, and definitely go carbon with the seatpost.
I think they're largely made to differentiate new bikes from older bikes because the new tarmac looking like the old tarmac year after year would probably hurt sales
I have actually wondered if adding a curve in the trusses of the rear triangle would increase the comfort/compliance much. Ideally the chain stay probably wants to be dead flat for the best transfer of torque through the chain but if the profile was flattened and some curve was in the seat stays then the truss arrangement would be noticeably less rigid. No idea if the uci rules ban this.
Peak Torque ......thanks for posting yet another brilliant video. The beneficial impact of what you do for us ordinary riders and the education it promotes is admirable, altruistic and simply valuable beyond any written words. I just wanted to let you know that....... As they say in the Lone Ranger film 'never take off the mask'
Thanks for not doing the clickbait-question title like most of the others.
must watch - you never thought how much these different seat stays designs would improve your comfort!
Having read the title....trust him, so I needn’t watch the video....like him, so I watch it anyway!😂
"Will THIS seat post design KILL you?" These kind of titles disqualify them self immediately from any time worth spending.
Doctor HATE him
You mean like this: "10 reasons why dropped seat stays will make you enjoy cycling again. You will not believe no 4."
Zoologist: Everything is crab
Engineer: Everything is spring
but but I thought the bike industry as a whole would never lie to take my hard earned money every year and laugh at me!
I know im asking randomly but does someone know of a tool to get back into an instagram account?
I was stupid lost my account password. I appreciate any tricks you can offer me
@Korbin Kingsley instablaster ;)
LOL!! All the marketing hype in the cycling industry is actually entertaining once you break the code on it. Especially entertaining on group rides!! 😀😀
@@rayF4rio Fun kinda ended when they decided to switch to disc brakes only on race/road bicycles and up the prices even more xD
I've always assumed dropped stays were a manufacturing hack to allow the same rear triangle to fit multiple sizes of front triangle
That too. Cost savings on a smaller steel mould too.
hey just like MTBs. Talk about trickle down
That would be easy to check if the angle starts the same between sizes
it's for aero.
@@PeakTorque there is no difference in mould cost
Very interesting video. Just to add some thoughts of someone who welds frames. From a weld up point of view (more so in ti, but also steel) dropping or raising the seat stays away from the top tube creates a number of alignment and distortion issues. Assuming a standard tack in place, dropped or raised stays will make twisting of the seat tube relative to the head tube likely, as well as there being a risk of seat tube being pulled slacker or steeper during full weld up. It can create stresses in the seat tube that make the tube want to rest in an S profile, which in turn will mean that seat post reaming will be unequal, thinning one face of the ID of the tube over the other. Titanium wants to move a lot in welding, and this sort of set up accerbates it. In a lot of ti bikes (and some steel) the top of the seat tube has a welded, thicker insert that allows a standard sized post to be used without shims, which wouldn't be practical with dropped stays, and finally it would be very hard to engage any sort of heat sink if the stays were dropped. All these issues can be resolved, but as this video very clearly breaks down, there isn't much point.
As someone who welds titanium bike frames on a daily basis, this comment has a value that, from a custom-build context, supersedes the aspect of comfort only. Also noteworthy that wall thickness in the seat tube and the type of seat tube/seat post interface (welded collar or insert) will play a huge role in the quality of the build as noted by Matthew.
But most dropped seatstay bikes are specifically designed that way and aspects like wall thickness/butting have certainly been considered/modeled/stress tested/engineered, at least more so than the average custom builder is capable of...right? How many round tubed dropped seatstay metal-framed bikes are out there anyway? When Paul built my Rock Lobster, he didn’t create a CAD model or put the final product in a stress test rig. I don’t think he even has my measurements anywhere except on a piece of paper.
@@kidsafe Yes, I would agree that most are designed for lowered stays (I would hope). The percentage is pretty small of round-tubed dropped seatstay metal-framed bikes out there. In my experience, as in many of custom builders, I would suspect that the request for this type of build is a much larger percentage than market average due to clients seeing this type of build (and marketing) on non-metal frames. In other words, I get asked all the time for this type of build. I built only one, many years ago, and decided to never build again for the exact reasons Matthew noted above. ps. You got a great bike:)
@@kidsafe Was only adding a bit of input purely from a steel/ti fabrication point of view, I don't have any real input or knowledge on the design or fab process of mass produced carbon frames. One note in regards to small builders and CAD. Up until recently this would have been true, but since Fusion was released, I have had access to (in the scheme of things) relatively basic but very functional FEA programme, which I can and do use as a sanity check/proof of concept etc... and know of other builders who use it in this way too. Most builders do not stress test their frames, obviously for one-off custom builds it would be financially unviable, but this is also because the basic design of, and materials used in metal construction have all been in use and proved to be incredibly safe and unlikely to fail in their intended uses. This is of course only from a design and materials sense. These bikes can still fail, but it will be due to manufacturing faults, user error etc rather than flawed tubing choice or frame geometry.
@@crisptitanium I was wondering if any of the tubes was dented, say with a crease type of dent, and actually it happened on the seat stay of a Independent Fabrications steel frame I have, and your end user wanted to restore the original strength, would you recommend silver braze fill, small welded patch or total replacement? I cannot find the tube material.(20 years old)
I was skeptical because being an engineer as well I always imagined it would have at least a small (if insignificant) improvement in deflection. Seeing the simulations really clears it up, thanks!
This and other people's videos about frame comfort make me realise I should really only choose my frame material based on durability and things like galvanic corrosion being a problem or not. (That's mostly why I'll stick to steel)
I'm already a huge fan of supple tyres for comfort, but now I guess I should also start looking for a seatpost with good dampening characteristics ;)
I have a nice steel frame & aluminum(?) seatpost. Have wondered about titanium as a material with more deflection...
You and Hambini are like the Tiff Needell and Jeremy Clarkson of bike engineering (in the) world on youtube. We need a bike build challenge for the both of you and one of Stig's cycling cousins to test them - who could that be? Could be something for Jeffers to do between whatever bans he'll be serving in the future.
I like that idea
But im heavier than jeffers by about 800% so I'd be a harsher test
@@PeakTorque haha yeah we need someone that can't hide behind a lamp post, just out of interest what height and weight etc are you, you look like you could lay down a watt or 2.
Jesus christ, imaging being compared to Jeremy Clarkson.
Exactly. Tiff Needell and Chris Harris would be a better comparison given the information presented. Though the way Hambini presents stuff is Clarkson-esque.
These videos are absolutely brilliant
Excellent breakdown, taking a vague problem to a quantified assessment. I learn something new everytime!
In your analysis, the bump load is a static load, but I would be interested to hear your thoughts about how well this approximates the spectral nature of road vibrations. It is close for the response for big low frequency hits, but not necessarily for higher frequency vibrations. There will be a difference between the compliance of the structure with a static load vs the transmissibility of random vibrational input from the base to the seat, but that will depend on the bike system modes vs the road vibrational inputs, which I have no idea what they would be.
Anyways, thanks for your thoughtful videos, I look forward to the next one.
Correct me if i'm wrong, but isn't vibration dampening much more to do with the frame material and tyres rather the the geometry
Hi mate nice video but I think you may have over looked a key point which may be worth investigating:
If a 2000N load is applied relative to the saddle then a corresponding load will also be applied to the drop outs (via the wheels) in the opposite direction.
Therefore it is likely that dropped seat stays will also allow the chain stays to flex more along their length, due to the reduced vertical bracing angle. This is likely to reduce the rate of force transfer from dropouts into the frame. I believe this is the bigger aim of dropped seat stays, I look forward to hearing your opinion on this.
For example of this idea please look at the Cannondale scalpel’s pivot-less rear suspension.
Yep, good point. To measure this i could plot the downward deflection of say the bb shell, but still, its to tiny compared to the seatpost.
Not just crack'n'fails either . Salsa el kaboing used a chainstay flex to preload the rear shock by 30mm for the rear linkage moved . Sunn also made a pivotless soft tail that didn't have a dampener.
@@PeakTorque No doubt the seat post is by far the biggest factor but I think the combination of seat tube and chain stay deflection could potentially move the design feature from markings BS, to the realms of plausibly effective.
In my opinion the best design so far is trek’s newest madone/domane isospeed: 100% decoupled seat post and ‘mast’ with a bushing pivot and an adjustable carbon leaf spring running under the top tube. This design allows the stiffest double diamond shape and good comfort but definitely adds weight.
Definitely agree on the stiffness claims...that said, any potential aero gains isn't ALL about frontal area reduction, but in improvements in drag coefficient. Even a completely round seat stay cross-section becomes "longer", and more ovalized (and thus lower Cd) when it is "dropped" more horizontal. If the seatstay is actually an aero cross-section, then dropping the stay makes it's cross-section a longer airfoil, which is going to be lower Cd.
The world needs a Peak Torque video every second day
Very interesting video. I was always sceptical with the dropped seatstays.
Been dying to watch this since you announced it, keep them coming mate!
Just by looking at the two models in the simulation I'd have made a guess that the dropped seatstays prevent the seat tube from moving freely in the opposite direction to the seat post, thus even making the frame more rigid.
This channel is a breath of fresh air to counterbalance the stench that mainstream cycling platforms churn out for sales.... Keep at the great work!
Whether they add to comfort or not, I find traditional seatstays much more visually appealing than drop seatstays. To Me, the perfect rear end in a bike would be of Salsa WarBird's (2019 and newer), followed by the Specialized Aethos', Giant TCR's and Cannondale Synapse (2018 or thereabouts and newer).
I also suspect (irrespective of my visual compromise of dropped seatstays) that dropped seatstay frames are more fragile than non-dropped designs.
I like the OG canondale supersix evo the most.
Spot on about weld fatigue. I had a MTB with dropped stays, the suspension pivot was mounted halfway between the BB and top tube-seat tube joint.
I cracked the TT-ST weld 3 times before the 4th warranty frame had a custom gusset to reinforce it.
Devinci moonracer frame in a large size, with plenty of seatpost length, and good insertion.
I have a aluminum gravel bike. It was very stiff and uncomfortable to ride. I swapped out the aluminum seat post with a carbon seat post and It made it a very comfortable bike for the long rides.
Thanks I was wondering about this. I have two aluminum commuter bikes. I put a suspension seat post on the boardman but the cannondale SAVE is noticeable in its comfort in comparison but will put a carbon seatpost on it at some point to make it more comfortable.
@@smallhatshatethetruth7933
I had bought a round seat post that was curved back. I took a chance of buying a chinese one. So far very happy with it. It does stick out quite a bit though. I think it's been 3 years ago when I put it on. Cheap, Cheap.
I had also had put Pirellis on my aluminum areo road bike. The carbon seat post was a true air foil shape it flexed side ways better than back wards. The wheels made it so much better than I had expected.
If dropped seat stays means lower peak load on the seat stay to seat post junction then for carbon that could be a huge advantage making the frame less stiff there which may impact ride quality
Thanks for the analysis and video. As a structural engineer, I've been wondering about the claim of dropped seat stay providing more comfort. It simply doesn’t make sense, unless the top tube also drops down. I really think the real reason for dropped seat stay is to reduced weight by using shorter tubes, which is a huge selling point in this weight concious industry. The seat stay tubes are compression mbers, and the failure mode is buckling, so the shorter unbraced length also increases buckling strength, perhaps resulting in thinner walls. In addition it provides a secondary brace point for the down tube. Perhaps this allows for a lighter down tube as well. It seems to me the stiffest rear triangle is a 60-60-60 triangle. So when you drop the seat stay, you probably don't want to drop it below 60 degrees from he chain stay.
Thanks for always ringing that it is tyres that impacts comfort the most.
You didn't mention flattened tubes, which I imagine flex a lot more.
Riding a Topstone Carbon I can say that with almost horizontal seatstays you can feel a lot of flex.
I really like the canyon seatposts with the leaf spring design, because they will provide great comfort while still keeping the seat level
When you hit a big bump its a really weird feeling as it whips back. It really deflects quite a lot, even with a lot of length inserted into the frame
Excellent video for helping design custom bikes.
Another disadvantage of dropped seat stays is that it will obstruct your view of the cassette when riding making it much harder to see what gear you are on
We shouldn't question big corporations bullshit, they don't want to make as much money as they can on us, by selling us cheap hyped up shitty products! Great video my friend!
dropped seat stays can increase comfort because it allows for a removing the back section of the top part of the seat tube. it increases the cantilever length of the seat post and therefore its deflection aka comfort. e.g. look at the Rose backroad or Rose reveal. It is basically the same effect that canyon tried to do with the seat post design of the aeroad.
The point about lack of fatigue testing on custom frames is interesting. I bought a custom Enigma Ti frame years ago, and after a couple of years it cracked at the head tube. They honoured the warranty and sent me a new one which was a couple of hundred grams heavier. So you could argue that the customer is doing the fatigue testing!
I'm no engineer and only have the most peripheral knowledge on these subjects but I intuitively felt that (if anything) the junction of the top tube and seat post would have the greatest effect on seatpost deflection. By decoupling the truss structure I imagined you simply leaft a greater tension force on the top tube/seat post junction/welding to manage but didn't improve "dampening".
Thank you for all your videos and giving me language for concepts I couldn't put words to. 👊👊
I have the Litespeed T5 lifted seat stays with a Ti set back seat post. I like that after a long ride on crappy roads in my area I don't feel all beat up. The frame feels springy especially on climbs, but in a good way. There is no doubt a carbon version would be stiffer and transfer power better, but I don't race and look for comfort over efficiency.
As a short rider my seatpost sticks out only about 10 - 15 cm. So I probably have to rely on tyres and bibs
Awesome video. Just what I was looking for.
Nice peek into the topic!
I hope for the future video you will plot frequency responce spectres and include second in-plane case: 100kg force on the saddle, sinusoidal vertical displacement of what are currently the fixtures (at postresonance frequencies, of course)
Would be also nice not to wait for as long as with the crank lenght followup, but who we are to judge...
I’d like to see how a Hellenic Seat Stay Design would compare with the two seat stay designs that you have animated.
Great content BTW! Keep it up!
So it makes a measurable difference, but not a noticeable one. Welcome to cycling marketing! :)
Great video. But surely the forks and seat stays can and are designed to act a suspension units. This video proves that the front main triangle stiffness is not effected by the seat stay design and the seat post is the main factor. But does not prove if the rear triangle design effects comfort. Cannondale and Specialised have for example produced designs that have been more forgiving due to the rear triangle design. Many Alloy bikes do this. If you model the front triangle as fixed and the load applied to the rear axle. Then surely you can isolate the effect of rear triangle and visualise the effect of different designs including different cross sections of the top stay tube.
Fantastic video. Thanks for doing this!
I'm not an engineer, but i would assume there's a energy transfer when the rear wheel lifts up from hitting a bump. Having the seat stays lower could potentially shift said energy more laterarly instead of vertically. In other words, perceived shock of hitting a bump could be transferred to the seat post instead of traveling up into the seat itself. Mitigation or cushioning of the Primary shock wave vs secondary.
Another way to think about it is the difference between hitting upward on the seat post vs hitting the side of the seat post. Yes there's a transfer of energy either way. However, there is a directional component to energy transfer and felt energy. 🤷🏻♂️
Its simply right. He forgot the vertical flex from forcepoint rear hu.
@Peak Torque, I dunno, I feel like you're missing something with your boundary conditions at the drop outs. Say for example the cyclist rides off a curb, the rear wheel will impact the ground and this impulse would be transmitted through the rear triangle . I recognize that the difference in frame deflection is minimal between each case; however, I feel like (*an engineers three favorite words*) the reduced MOI of the rear triangle should be significant enough to offer a lower effective spring constant and thus absorb more of the impulse. I'm no expert in FEA but is there a way to simulate the case mentioned and provide an effective spring constant for the rear triangle of a conventional vs. dropped seat stay?
What about a cluster like the Lapierre Xelius? The top tube connects to the seat post but the seat stays do not. The seat stays shoot past the seat post and connect only to the top tube mid span. This connection may be less stiff then a traditional one but in the end it’s still a frame with the same support conditions at the dropouts so it’s probably very similar. The cantilever seat post and tires will almost always provide the bulk of the deflection as they are the softest spring.
Disagree ,Your FEA are maybe wrong, seat stay can deformed in differents planes, I sized bike in the industry , it has been validated that it is more compliant. I usually agreed with you , i like your channel, but this one you will have to re- evaluate
I just started watching your stuff. It’s very good and we are aligned in many ways. I’ve always told people that the seatpost has the most impact in ride quality. I will share this with people from now on.
You mentioned speed wobble. Have you ever done a video on this topic? Would you consider Doing a video on this topic?
I'd also like to add that a combination of 11-17º top tube slope and seatstays that continue from the top tube base will not only look infinitely better, but also yield the same or greater compliance as a combination of a [near-]horizontal top tube and dropped seatstays. As yet another bonus, it will be less delicate than dropped seatstay frames. A lot of advantages (including a visual appeal) - and not a single disadvantage for sloping top tube & normal stay design.
this is the third video from your newly discovered channel i am watching in a row (subscription right on the first one) - other two being about why those cranks fail and stiffnes of hubs clamping. few more tabs i just opened to be watched after this one. if i was gay, i'd hope you are and propose to you. wow! conclusive, logical, reasonable, plausible. my bikes were made between 1960 and 1999, thus your topics don't even cover my own fleet, yet i am soooo curious into your engineering knowledge. thank you!!! i love you.
Going by this logic, wouldn't Giant's (and others) compact geometry be slightly more comfortable as there is usually a greater distance from top tube to seat, giving more flex in the seat post?
So riding a small frame with a lot of exposed seatpost and 28mm or larger tubeless tires is the most comfortable option. Bonus point is, that you can use the stiffest frame there is since it makes so little difference.
I know this has no engineering criteria, but i hate the look of dropped seat stays. 🤔😆
Just as a side note, the rear end of the triangle has changed considerably with the introduction of disc brakes, wider hubs and wider tyres. I do believe this design change is more about accommodating these design changes. It is a smaller triangle with thicker seat stays to accommodate the lower angle. This would make the triangle more rigid. Something to consider maybe?
Might be a different equation for a carbon fibre lay up - less stiff seat and top tube with stiffer down tube, chain and seat stays. By dropping the seat stays you then allow the greater flex in the seat and top tubes to operate? If that is accepted then the dropped seat stays on the alloy version of the bike may be more about matching the aesthetics of the better performing carbon frame.
the sickboy's look is suited you well, all we need is some scottish accent from you for next video
😄 ...and some 🛌 sheets that have been crapped in
Am I the only one who's slightly disturbed by the thought of the dropped seat-stays applying forces to the unsupported middle of a tube?
It's not as if the strength of the seat tube is compromised in tension at that point except of course the bottle bosses. But in reality I wouldn't think you would be getting anywhere near the yield strength of any frame material.
Proper seat tube angle 👌
I asked my Ti builder guy about this and he 100% agrees. Very low benefit of dropped stays, for higher risk (or greater weight).
Thanks for the knowledge!
Only constructive thing I might point out is audio levels on this production, but that really is a minor thing.
Isn't it wonderful we're nerding out over the minutae of a centuries old design in 2021. None of it matters, but it's great fun.
What jumps out to me is that the model of the dropped seat stays shows the head tube anglular deflection occurring which could mess up braking or steering control (see 7:30). Dropping the seat stays introduces a needless pivot fulcrum.
"Even your choice of bib shorts and chamois has more deflection than the frame". Brilliant. Now I need more vertically compliant chamois. What a great new marketing tool for cycling clothing manufacturers.
They’ll be a new generation of endurance compliance saddles soon probably like the old selle Italia turbo or may be a modern saddle with a deeper saddle rail.
This was super interesting, could you model a triple triangle design to see how the same area would behave under load?. Or even if the triple triangle is even as groundbreaking as the marketing claims make the technology out to be?
I like your engineering analysis of bike tech, but I feel like this one is missing something. You assume "comfort" only for a seated rider. The saddle is only 1 of the contact points for the rider. You ignore handlebars and more importantly the pedals, and don't account for a rider that isn't seated. If you consider a gravel bike on a bumpy descent where the rider is standing, or a roadie in a supertuck that smacks into a pothole, the seatpost deflection has no affect and it is the rear triangle that has to absorb energy before it is transmitted to the rider via the pedals. I'd love to see this same test done where the stress is done from the rear dropout.
Very enjoyable! I’d be interested in your thoughts on designs where the seat stays are not fixed to the seat tube - thinking here of the Trek IsoSpeed design, and the linkage on the Cannondale Topstone.
Also, as a very light rider, who rides without layback (seat pretty far forward), I always am thinking that any supposed compliance is going to be even less, given that I won’t be acting as as big a lever as a heavy rider with large layback.
I was thinking about the Cannondale as well. Although the pivot point allows a rotation between the seat stays and the seat tube, I suppose that the actual effect (a higher translation in the z direction in order to increase comfort) is mostly depending on the stiffness of the seat tube and seat stays. When both are stiff as hell, then the pivot is useless. idk
If you're referring to the GT "triple triangle" design - the increase in vertical compliance is going to be even more negligible than what was shown here. Back in the 1980s when tubing diameters were considerably smaller than current designs the "triple triangle" increased the rigidity of the seat stay, seat tube and top tube as well increasing the strength of the whole area. In the past quarter century the bike industry has gone away from lugged steel and small diameter tubing thus negating the design positives. A standard double diamond bike frame design is more efficient (slightly). Another negative for "triple triangle" type frames is the considerably greater Heat Affected Zone (H.A.Z.). The reason for butted tubes used in bike frames is to counteract the tubing being weakened during welding/brazing. A greater H.A.Z. requires a longer area of the tube(s).
Yo man how are the custom steel rotors coming along? Still interested!
Trying to get the price down.
You have been mistaken, in both instances the peak stresses are lower for the dropped seat stays.
You have made my mind. Think about it, the double diamond frame would be the strongest if both triangles were equilateral. The dropped seat stay frame looks closer to an Isosceles' triangle distributing the load equally across the seat post welds. The peak weld stresses illustrate this perfectly, normal seatstays have weaker seatstay welds.
Great stuff as always
It looks sick though
Looks good on bigger size bikes. A bit awkward looking on the smaller size.
On aero bikes I have noticed a much stiffer ride. Sme of this might be tyre (higher pressure) but from the video series I am going to guess a huge part of that is the seat post shape. So if ''compliance' is an issue on aero bikes, then surely going back to a round seatpost while keeping all the other members aero shaped would be a happy medium?
@Peak Torque... You proved that dropping the seat stays actually does provide more lateral deflection at the seat thus providing some marginal suspension. (Some is better than none, correct?) 7:52
Okay. 1.25% more deflection :)
Very educational, thanks for that.
Dropped seat stays combined with a compact frame (aggressive sloping top tube) result in a longer seat post with more flex/deflection = more comfort.
Of course, high gains in comfort result with lower bodyweight i.e. sub 12% bodyfat.
However, bike manufacturers cannot lever sales out of that factoid.
new bike trend: No seat stay and top tube for more comfort. On the other hand, the seat tube has been made into an I beam for some aero reason
It is right if the the force comes from the saddle, like in the video.
BUT Look at the force point in the Center of the rear hub. Look at the vertical tension and flex, you Look only on the horizontal from the saddle.
I'd like to suggest a tweak in your modeling that may dramatically change your conclusion(?) Argument "for"
I've always *assumed* that (to increase flex) for the droped seat stay to be effective it must be *combined* with a "thinned" seat post croass section (ostensibly for tire clearance).
(Assumption) The point of low area moment (the "flatest" cross section on the seat post in front of the rear tire) creates an opportunity for the designer to tune in the flex amount AND rhe seat arc they're seeking (for the seat total system (=> increased repeatability of flex/ride between different riders).
The design enables a engineers to control net Flex much more precisely. Controlling the flex Pivot Point ( down near the bottom bracket). => dramatically changing the Arc of the seat (effective arc length 2.5x ro 4x?). It will mitigate the seatpost height and frame seatpost overlap effects that dramatically change Flex/"ride" between riders (w/different leg lengths on the same frame size).
As handlebar width is adapts (to shoulder width) as frame size increases, this "hinge" can adapt as riders weights increases (w/larger frames) use slightly different seatpost extensions.
Seat posts would fine-tuned ride versus be the primary device.
Surely the dropped seat stays would increase potential deflection in the y-axis, ie left-right. After all, the load on the bike is going to be alternating from left to right as the rider is pedaling, so dropping the seat stays, which hold the seat tube rigid, would allow lateral flex. Obviously fore-aft and vertical flex are still restrained by the top tube, so any change in deflection there will be minimal, unless you go for the full-on MTB compact geometry, and elongate the seatpost. But lateral compliance will still occur as the rider applies a downward lid to the bottom bracket on each alternating pedal stroke.
I say this as someone perfectly happy with my traditional diamond frame bikes, but I think there’s more to the dropped stay design than your analysis is showing.
As others have said, allowing for flattened stays should also figure into the analysis; I can definitely feel more grip in the rear wheel of my CAAD10 than in other similar bikes with round stays.
Where is the frame constrained? Is it at the dropout and head tube(fork) only? Is the bottom bracket shell constrained?
I would have expected the bottom bracket to move down very slightly under compression, and the seat stay to really push into the seat tube.
While a metal bike with dropped seat stays shouldn't have much more deflection, I would assume that combined with varying of carbon layup, the dropped stay would allow for quite a bit more bowing of the seat tube.
Constrained at the rear dropout and sliding constraint on the headtube lower race in the horizontal plane. So yes the bb can deflect downward.
@@PeakTorque You should probably model the rear dropouts, some sort of fork, and hubs. Get rid of the fixed constraints if you really want to examine the difference.
They look good thou.
I’d be interested to see how sloping the top tube effects your model.
Giant have been sloping the top tube for years. Personally I prefer the appearance of a flat top tube but I suspect it’s less comfortable.
I agree it's in the seat post, but what you have missed out is that the comfort or compliance really also depends on the foreaft of the saddle placement due weight
As someone with a custom steel frame and similar body measurements, it would be interesting to look at the top tube angle as it modulates the flex. Mine is a 6 degree slope, which is for whatever reason considered a standard (10 years ago when it was made). But as you're thinking of building one up, it'd be an interesting exercise.
When I was younger, I don't remember anyone ever discussing comfort with regard to bicycles... unless they were balloon tired cruisers, or some kind of bike aimed at senior citizens. They're supposed to beat you up a bit.... no? 🤣
The dropped SS appear to normalize the weld stresses for the two points you looked at. That would appear to point to dropped seat stays as a better overall design. Not for comfort, but for long term weld durability. But I’m wondering where else the stress may have increased. Normally trade offs aren’t free.
I prefer the traditional look of the seat stays reaching the top tube, and in my limited knowledge I thought a shorter tube would be stiffer than a longer one. I own two Lynskey's one Helix pro and a 460 and both are stiff enough to race on and I am 6ft 5in and 190lbs.
I'm No engineer. I can See Yor Frame model flexing. Where is your model fixed: - Bottom bracket ? ( It Looks Like that )
Or
- lowest Point of the headtube and both Rear dropouts? ( AS whilst Riding the load would be hold there. The Bottom Bracket should have at least SOME groung Clearance 😅. )
Reason for the question: the Quite Low seatstays of the Cannondale Topstone. Those Stays act Like a pushrod to Bend the seattube. Add to that a flexing Point in the rear Part of the toptube and voila: Suspension!
Or am i Missing a vital Point Here?
But what about deflection up in the chain stays. Does the drop seat stays effect that? Like the way Moots YBB micro suspension uses chain stay deflection as a suspension.
Ya, can the dropped seat stay itself bend? Resulting in more comfort as the angle of attack of the bumps might be different comparing to a higher seat stay? I noticed my Caad13 dropped seat stay looks quite low so it could bend in itself as the bumps are hitting it upwards?
There will be chain stay deflection but you'll notice that Moots have used small diameter chainstays to allow the YBB seatstay up to 20mm of travel. Many chainstays in Ti builds these days use at least 1" diameter tubes and 0.9mm wall thickness which is noticebly stiffer when compared to my old 94' Serotta Legend (
Hi, Thanks for the informative video and the modeling. I think that your model may have given a result associated with the material choice and not the frame layout. As you probably know, Aluminum is more flexible than Titanium by nature. Young modulus for Aluminium is 70 GPA, whereas Titanium is 120 GPA. I think that for your model, you should change the material choice to be either Titanium or Aluminium for the frame and Seatpost, that way it would give a better output for the frame design only. Thanks
Physics will not be denied 😁. Aerodynamics or no aerodynamics, a tube attachment not at a node has every structural engineer ever turning in their graves. It's a testament to the fatigue properties of catbon composites that such crimes go unpunished.
The model is 'if it looks cool, it will sell'. Everything else is marketing spin.
I have canyon leaf spring seatpost for my hard as rock aluminium bike lol budget combo, but amazing results 💪🏻
I think the aero gain of dropped stay is less of the reduced frontal area, but more from better shape. Consider round tube, angle it a bit and cut horizontally, you get an oval-ish shape. angle it even more (dropped stay) and it become even more oval with longer cord length.
True. But at this Reynolds and Dimitriev that chord length is so small its smaller than all the local vortices, so it probably won't make a difference.
Now I'm worried about the significantly higher and more localized stress at the SS-ST weld. How come it is so much more stressed than the dropped seat stay. I would have expected the exact opposite case. It could become the main reason to adopt the dropped seat stays.
Now thats a surprisingly predictable result - thanks for the analysis, great work👍
Now try the effects of using smaller diameter seat stays and different wall thicknesses. The results may surprise you...
Cheers
Would love to see an analysis of the old GT Zaskar stays that joined at the top tube.
And the claimed flex of the seat stays on the gt grade
Hmm. Interesting, but I don't think this really addresses the main claim wrt compliance, which is that dropped stays decrease so called 'buzz' or 'chatter', i.e. high frequency noise rather than visible bumps in the road. Some implementations do have actual suspension elements built in so I think your question would be more suited to those specific builds. As you say, your model is very simple and side steps looking at an actual frame from a manufacturer in conjunction with their specific claims. Can see why you might want to avoid doing this though.
Nice !
Its all the same for " aluminium ", " steel or stainless steel " and " carbon fibers " frames ?
Idea for a next video
Myths and reality about Integrated Seat Posts ( both in metal be it steel, ti or carbon isp ) .
They are mainly gone from nearly all productions bikes. But some small and not so small custom builds are using them. Mainly for anesthetics I guess. They also reduce practicability for travel etc. But speedvagen for example make some bolds unproven statements about them.
Thanks
Have a good one
You good sir should sell those frames on the mass market. It's so damn hard to get high stack/short reach frames, and who wants to get a current Domane/Roubaix/*Insert a Truck's Name* anyway ?
I wish this video came out 3-4 years ago when dropped seat stays hit the mainstream market
Do dropped seat stays look bad-ass? Yes.
Not an engineer but just looking at what you have modeled it looks like you are only thinking about how the whole system reacts to a person just slamming their butt downward on to the seat at a standstill.
In terms of what actually happens when you ride the bike out on the road you have to consider the force of the tire hitting a pot hole and that force being send upward (not completely from top to bottom but at some angle like 11 o'clock) this would depend on the impact but something like that should send an upward force starting at tire - rim - spokes - axle - rear dropout - frame tubes - seat post - seat - then finally your butt and then the rest of your body ending with your hands.
So a force then coming into the rear dropout upward and slightly back is going to flex the bottom stay where it rotates a little around the bb, but the topstays would be pushed upward where if not put into a hard intersection like a traditional bike that has a top tube right there it could instead flex the seat tube a little and not send most of the impact into the seatpost and cause more bending there.
Either way thanks for the vids, and definitely go carbon with the seatpost.
I think they're largely made to differentiate new bikes from older bikes because the new tarmac looking like the old tarmac year after year would probably hurt sales
you are very good - you pull the sword to all the cycling industry marketing dribble - well done
I have actually wondered if adding a curve in the trusses of the rear triangle would increase the comfort/compliance much. Ideally the chain stay probably wants to be dead flat for the best transfer of torque through the chain but if the profile was flattened and some curve was in the seat stays then the truss arrangement would be noticeably less rigid. No idea if the uci rules ban this.
Peak Torque ......thanks for posting yet another brilliant video. The beneficial impact of what you do for us ordinary riders and the education it promotes is admirable, altruistic and simply valuable beyond any written words. I just wanted to let you know that....... As they say in the Lone Ranger film 'never take off the mask'