Anti-Squat Suspension Geometry - Explained
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- Опубліковано 12 вер 2024
- Anti-squat suspensions are used to reduce body squat by altering the rear suspension so that the forces resulting from accelerating pass through the control arms and suspension linkage rather than through the coilovers or struts. This is typically done with vehicles with high power to weight ratios. By reducing body squat, the rear wheel geometry will remain more consistent, and the vehicle can maintain a specific ride height which can be beneficial for aerodynamic purposes as well as driver control.
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We just reviewed this video and it had some great information. One detail we should be pointed out is that for an IRS the green line that goes through the IC is drawn from the hub centerline because with an IRS the torque reaction is taken by the chassis no the ground. This makes it very difficult to get much more than 25% AS with conventional IRS geometry. Ford gets more with S550 IRS because of the Integral link concept.
Cortex Racing...where can I find info about the IRS and AS and the torque reaction??? Thanks...I don't believe the info presented here was totally correct. AS value is not measured on the vertical at the CG but on the vertical at the front spindle with 100% AS being where the CGs horizontal crosses the front spindle vertical. What was being explained here was the % of Rise typically used w/ ladder bar suspensions and the amount of tire sidewall crush on the launch. 50% being the metric used where >50% being more and
You should do a vid detailing the differences and the advantages/disadvantages (packing, dynamic & static camber curve, toe-in/toe-out under dive, etc) of various suspension systems (double wishbone, Macpherson strut, various interpretation of multilink systems, etc).
54 years old and after all these years I finally figured out how to Google this wonderful basic explanation, which I knew but could not explain this succinctly. Bravo. Thank you so much. Now I can rest. No, I am not being sarcastic, this seriously made me happy!
You are doing really a great job! As a former teacher (Automotive) I have some points to make it even better:
Give us a moment in the video where we can see the withe board complete without arms legs heads in front so we can pause and study
Not every body (me ie) is English so please .. we are not in a hurry, talk i little bit slower and take some pauses for us to think and absorb.
You impresse me with your knowledge thats very good! So keep on doing the good things and thanks for your explanations!
Anti squat is a very important chassis design feature for getting power to the ground for good acceleration on powerful rear wheel drive cars. Weldineer stated correctly (below) that the anti squat reaction to the torque of the axle lifts the mass of the vehicle resulting in an increase in downward force on the tires.
I would add that the most important thing this does is create positive traction feedback to allow even greater torque to be used in vehicle acceleration. What do I mean?
When you nail the gas in a car with a lot of torque the tires will slip (spin, burn out, etc.) once the torque exceeds the the traction available at the tire contact patch. The traction depends on the coefficient of friction of the tire and roadway interface multiplied by the downward pressure on the tires.
Anti squat uses the torque of the motor to increase this downward pressure on the tires.
The anti squat reaction lifts up on the car and pushes down on the tires. This extra push down increases traction. The increased traction allows more torque to be applied. The additional torque pushes the tires down harder on the road again increasing downward pressure and again increasing traction again increasing torque . . . .
Taken seriously this positive feedback loop allows enough traction for the lift of the entire car from the road surface before the tires loose traction (see wheel stand! ) and sick levels of acceleration.
Lack of anti squat in a powerful car means nice smoky burn outs but slow off the line and on road courses slow out of corners. Ask any Fox body Mustang owner about getting the 5.0 torque to the ground without smoking the tires. That is why Griggs Racing sells so many GR40 traction kits for the Fords; they add a torque arm to the axle which gives the chassis anti squat and really allows the car to hook up.
Thanks EE for all the cool videos!
Keith Soreng so what do u think how much anti squat will be best for designing the rear suspension geometry?
My second comment just to add that this is a great explanation, the best. He clearly explains in easy to understand language and helpful sketches what AS is, how it comes about and the pros and cons.
This is why I love engineering.
Thank you so much....!
I have learned all vehicle dynamics from you.... Thank you very much..! 😊👍
isn't squat necessary to put more weight on the rear tires to increase traction in a rwd car? you did say so in the video about the dodge demon or am i missing something?
Also, I'd love to hear your thoughts on live vs independent axles. And maybe a take on the ford TTB system.
Happy Birthday Bro!!!
Nice work
Thanks a lot
-Student at UNC charlotte
good video, correct anti squat is gold in drag racing, but for circuit/road racing the angle of the bars to achieve 100% anti squat will produce huge amounts of rear roll steer.
Hi! I really like your videos very informative. Do you have a degree in automobile engineering?
very good explanation! :) I know some suspension lingo for cars but this was a new perspective for me
The camber shown would be for an IRS rear. You won't have that with a solid axle rear.
what about solid axle rear differentials? The contact patch stays the same no matter? Does the effect of acceleration on the car translate somewhere else in this situation?
I dragged my lowered AE86 and because the lower control arms were not horizontal rather at 5deg I had massive axle tramp when I launched the vehicle. I managed to reduce this using "traction brackets" bolted to the axle housing which returned the bottom two lower control arms to the factory angle. However the top control arms are still facing at say 10deg, and they are shorter. I could fix it by boxing up the rear floor pan to run equal length control arms and return to factory position but its just a street car...
rotormaster I don't know about your AE86, but with respect to live rear axles, I believe you're right that the contact patch remains constant. They're great for drag racing.
rotormaster
Anti squat still affects a solid rear, and not because of camber change. You will get more traction on the launch because the force going through the control arms is extra force seen at the tire. If you look at some drag cars, they actually LIFT in the rear on launch. The sum of the vertical force at the tires are HIGHER than the weight of the car, because equal and opposite reaction. The mass of the chassis is going up, because the control arms has a force lifting the chassis. This force is also acting in a DOWNWARD direction on the tires, thus more traction :)
You can calculate the side view instant center and therefore "anti squat" for you car, there are plenty of resources showing the math of this for solid rear axles.
rotormaster I went for a ride in a friends rx7 that had about twice the power of mine (near 400hp) his springs are so bad that the whole diff was twisting and the drive shaft was hitting the body.
Pitch moment also affects the stall characteristics of aero tuned cars
But with a double A-Arm suspension like those Baja Trophy Trucks, the upper control arms retains your camber, doesn't it? At least thats what it looks like until they reach the end of their travel. Obviously with a solid front end, you get a camber shift as you dont have that upper control arm to retain your camber. Correct me if im wrong please, and I love your videos
Slapa Hoe Both control arms will determine your camber. All control arms are used to calculate the instant center, which will determine camber change with wheel travel
Hey man, i watched alot of your videos and they're great! love them!
I'm a pc gaming fan, and i was wondering, have you tried game called "Automation" (plenty of vids here on yt), I would like to know what you think about that game, since it's so technical and detailed. I get that you're busy man, so no pressure
Hahaha
Let me check that out
hi, i think you put the 100% antisquat line in the wrong place, the line should pass through the hrozontal height of the centre of gravity but over the opposite set of wheels, if it passes through the centre of gravity it will unload the front wheels and lift the front of the car and the rear of the car, which is in effect over 100% antisquat.
Engineering Explained
What is a good track set up for a car's anti-squat and anti-dive characteristics ?
Could you explain the practicality and risks of the new Hankooks iFlex airless tire?
Say you want a car closer to the 100% anti squat for better straight line acceleration. Knowing this will affect cornering, can you adjust your toe or camber to offset the negative affect of the anti-squat on your cornering for the best of both worlds?
Band-aiding suspension issues is never a good thing. When theres an issue present and you band-aid it at one certain scenario (squat for example, under power/heavy load) then you will very likely have sub-optimal geometry at other scenarios (neutral load).
So can we get a video on Koenigsegg's Triplex suspension?
Interested in a detailed video on their anti-squat design.
Would you say the same improvements that drag racers get from improving antisquat percentage could transfer over into drifting ? I realize you said in road racing it may not be very beneficial, just a thought I had being a drifter myself looking for more mechanical grip wherever i can get it 🤔
What about 4WD and FWD cars? Do they need to have anti squat suspension and if yes why is that? Great video as well
Menel Dimitranopoulos I would say with FWD it doesn't matter much about the contact patch in the rear, which is why most FWD drag cars run what look like bicycle tires in the rear...but it needs to be stiff in the rear because if the rear squats (COG moves back) then the front won't have as much weight over it which will lower traction.
MrSlowestD16 Thanks a lot!
Menel Dimitranopoulos
4WD yes, FWD no. In fact, it's not really possible for a FWD car to have anti squat rear suspension. To have anti-squat rear suspension there must be rear tire force, and since there is no rear tire force, there is no anti.
Instead, for quick vehicle response and increase front launch traction you would have pro-lift.
4WD could have both :)
Is there a practical way to find the center of gravity of a vehicle?
***** Could be done using scales and a slope of a set angle. You'd need to measure the angle and then do some math, but certainly could be done.
Hi, I enjoy the video, I have the question of what happens if your anti-dive go higher than the center of gravity ? What would be the effect on suspension?
Hi. I could use a little help with something I'm trying to figure out. So, for vehicles that are considered to have too much or too little anti squat, a common practice is to use subframe spacers to essentially tilt the sub frame for more or less squat. For example, in the case of my vehicle, the claim is that using thicker spacers in the front than the back thus tilting the subframe down decreases anti squat. From explanation, it is said this is caused by the spacers adjusting the instant center. Is there a simple way to determine how much the thickness of the spacer will adjust the anti squat?
Hello!? 2 years no response? Throw me a bone. Reversed upper link. Which way would you move the frame side(which is behind the axle)to increase antisquat? Up or down ?
Thank you for the great video! Would you review GM's HiPer strut for Buick LaCrosse and Regal.
Hi good nite.. I have a question hope u can help me .. I don't know much about this.. I'm building a rock crawler.. I hear about anti-squat and anti-dive.. what's it's better? High anti? low? Or neutral? For rock crawling?
Is the above calculation valid only for cars having solid axle geometry or is it true for cars having independent suspension too?
How about Koenigsegg's Triplex suspension (anti-squat) they are not linked to the suspension but rather is a push rod actuated system, it sits on top of the whole suspension and engine, but I don't know the mechanics of that, although it's their secret, I'd love to know basically how they work or, like a certain suspension setup or something?
that's a good explanation of anti squat. given the right amount of control arm length and stiffness you can achieve an greater anti squat than 100% which would raise the rear end of the car... just saying haha
How is the antisquat determined when you have a reversed top link? My car uses a rear mounted sway bar that is also the top link.
Is anti squat/dive geometry preferred in non sports car?? If yes, what are the percentages?
In practical uses, what are the general values of %Anti-Squat in an ATV/Vehicle ?
How does this modify the position of the roll center? All the information I’ve read shows that the roll center is calculated with the inclination of the suspension arms on the YZ plane, however none shows the combination of both geometries.
Late reply but antisquat has nothing to do with roll center. Draw lines from contact patch of left side to to instant center on left, do the same for the right; intersection of those is roll center. For rear IRS do the same thing, for live axle the conversion of links, swing of panhard bar or the rotary joint of a watts like establish roll center.
is % anti squat the % of the total weight transfer through the suspension links from an acceleration event?
Very helpful
Where do you get all this stuff from?
what should be the anti squat % for independent suspension (rear-monoshock supension) for quad bike?? ...and what are results if the %less or if the % is more?? please reply .....thanks in advance
What about for recession suspension geometry at the rear?
When they meet at the other side of the tyre?
Does anti-squat amd anti-dive affect the suspension springs stiffness during normal straight line motion and during cornering also ???
You actually don't explain much, just say "this is how it is because it is like this" in a bunch of different ways
do more vids for old school muscle cars...that rear end is an irs, not really applicable for the older solid rear axles
How does this work with trailing arm IRS set ups? When a lower swing arm is used.
So what would be the best anti squat percentage for race track with lots of cornering
Pretty much the same as anti-dive except in the rear. But this time it got me thinking: it seems like you need double-wishbone for anti-whatever (which is expensive and heavy) but double-wishbone should also mean: no camber change when height changes. Is it true and if not, why?
Not really heavier, just less compact.
xod You can have anti-whatever with solid axle, mcpherson, pretty much any suspension geometry.
Depending on the geometry, camber will change when height changes. Most double wishbone suspension will have camber change with height. The exceptions you might find are most likely in off road vehicles
I don't understand why this green line only goes until the Gravity Centre Vertical Line, while in other videos from youtube (like college classes) the green line goes until the Middle of the other wheel.
Can any one help me?
Have you powered a video on hemi's. I would love to see how these engine are different and white board.
Justin Smith ua-cam.com/video/qLns7ibeUps/v-deo.html
Can explain the importance of contact patch
According to Milliken and Milliken, you are not right about how to find the percentage of anti-squat.
They claim that it is the ratio between the height length ratio of the IC and COG.
Let's say we have the following:
a horizontal distance from rear wheel contact patch to IC of 4
a vertical distance from rear wheel contact patch to IC of 3a horizontal distance from rear wheel contact patch to COG of 6
a vertical distance from rear wheel contact patch to COG of 5
They say: %anti-squat=tan(theta)/(heightCOG/lengthCOG)*100 or in other words: %anti-squat=(heightIC/lengthIC)/(heightCOG/lengthCOG)*100
In our case that will be %anti-squat=(3/4)/(5/6)*100=83,3% according to Millikens
You say the relation is the height of the hypothenuse for the IC extended onto the line from the ground to the COG compared to the height of the COG.
In this case the height of the hypothenuse for the IC extended onto the line from the ground to the COG is 3/4*6=4,5
So you claim the %anti-squat=100/5*4,5=90%
Are you sure about your explanation?
How much percentage should we maintain for off-road vehicle double wishbone suspension can you say pls
What is the desired anti squat value for Sae Baja car.
Wait but wouldn't you not even need this if you had a live axle suspension in he fist place?
Oddly specific to a problem I am experiencing with my older vehicle: squat due to spring sag.
is there anything on pro dive, squat, lift ?
Videos about chassis please... :D
Squat looks cool in photos tho :P
+Liamv4696 That's camber you're thinking of.
Jake Ramsdell No i mean the squat produced from hard acceleration. Check out the drag racing video on my channel and youll see what I mean :)
Geez, it's a wonder why informed people bother to go to the trouble of explaining something when a lot of the comments below shows a lack of basic understanding of suspension and comprehension of what he is talking about. On the subject all I'll say is to note that anti squat reduces suspension compliance, you don't get something for nothing.
The anti squat suspension is even more important in rear engined cars like the 911, right? As they tend a lot more to squat their heavy "butts" lol
is anti squat suspension geometry a substitute for anti roll bars?
+honna4949 Nope, ARB typically won't affect squat as the whole axle raises or lowers.
+Engineering Explained hey man. thanks for the reply. but as you go through a corner, with anti squat geometry, you will be putting your roll load transfer through your control arms and chassis instead of your coils. doesnt this beat the purpose of an anti roll bar?
How would you set up a solid rear axle
Exactly the same way. Some are even setup to have more than 100% anti squat, they lift the rear suspension
so many things are wrong with your video. 1) you cannot four link an independent rear suspension or effectively build in anti squat, you can only do that on a solid rear axle, there will be no camber change from suspension travel 2) the line doesn't go from rear tire contact patch to the instant center ( four link intersect point) it goes to the top of the front tire vertical center line 3) when the line is in the proper place if the instant center is above that line you will have anti squat if its below it you will not
So 100 percent anti squat will not squat? Or it will squat the most? I'm confused!
clarkie005 Something that is "anti" will try to prevent whatever word comes next. So in this case, 100% anti-squat means no squatting. :)
Engineering Explained What happens if it exceeds 100%?
MrSlowestD16 Lift! (not including tire squat)
Of course, a suspension with 100% anti squat still may squat, since the percentage calculations are a simplification of jacking force
Oh god instantaneous centers, I hated the Norton book!
what are the effects of negative anti squat?
Less grip since less of your tire is in contact with the ground. The less grip will make the car more prone to oversteer since most of the negative squat will be in the back. The car won't be able to launch very quickly either , altough when the car has got some speed it will most likely not be very affected by the squat since the car won't be powerful enough to create much squat.
thanks alot...
I will have squat suspension for that stance look lol I'm joking.
I dont think he fully understands what he is saying.
No squatting, no booty. Fact.
Fax
Ok if you have a girlfreind this is da easiest way 2 impressed her with the car! It shows you have a lot of power in your 90s 4 door civic!
Can't anti-squat and anti-dive exceed 100%? Given your seemingly arbitrary definitions of these "dotted line features", surely this is practically possible?
dgmcl3284
Absolutely! Over 100% "anti squat" will lift the vehicle, so "pro lift" (of course anti geometry does not effect tire squat)! The % anti-whatever calculations are simplifications and are mostly used to describe your suspension to someone, not to do vehicle dynamics simulations. Jacking force calculations are better used for simulation and determining how a vehicle will behave.
Jacking force can be calculated by know what your longitudinal tire force is, and what the angle of the green dotted line is.
look up dirt track modifieds. They run an 8" tire on dirt, so they do not get a lot of traction. However they do utilize a solid rear axle and much more than 100% anti squat. It creates traction two fold. Weight transfer through the links instead of a spring, and shortening the wheelbase up to around 4"(depending on the setup). Food for thought, radical suspension systems in a vehicle.
less overview and more on the application! most use if its not broke don't fix it ideals.... are you.... point is; leaf-springs on my 1979 and struts on my 1993.... is this for someone custom building from nothing
What if my car wants to have a nice butt? Squatters are keepers 👌🏽