I remember a motorbike magazine did a cool test about 15yrs back. They covered over the speedometer on a bike and got three different riders to go along a runway at whatever they thought was 30, 50, 60, 70 & 100mph. Of the three the guy who was a speed freak was actually the most accurate, while the worst was a copper! Could be a cool test to try, especially if you used a big comfy car vs the mx5!
What would happen to different types of race cars if they encountered a pothole? Even on street circuits, this has to be an extremely rare occurrence for today’s race car drivers
15 psi is the best pressure to contact patch ratio. Because any lower will actually decrease your contact patch as the tyre tends to fold in and you have what it's called "shoulder wear", when central part of the tyre is actually lifted off the contact surface and you are running on the two edges. It's quite easily identifiable just by looking at how they were worn out. Plus, the most important part of it is the make of tyres itself. And I'm not talking about brand, but what they're made off. Some tyres could be were hard composition of rubber, some will be very very soft. From my own experience the softest tyre I've ever had on my car was Michelin Eco tyre, I don't remember exact model name, but that tyre was so soft lightweight and flexible that I was able to turn it *inside out* and that shocked me.
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The ideal pressure depends on the size of the tire (and of course on the car it is fitted to and especially its weight). It doesn't really make sense to compare tirepressures between tires of different sizes or between different cars.
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@6:40 not sure the gains are even real. you had to try twice. i think rolling resistance is just as important for such a low power car when doing this, and high pressure has the advantage there, even with only the rear tires being pumped. pump all four tires to 50 psi and you'd have your best time, specially in 1/4 mile or longer runs.
I had a MR2 with ultra low profiles and got a flat rear tire, the sidewall was so stiff that I couldn't even feel the flat below 30mph! Drove all the way to the local asda and shredded the sidewall! 🤣🤣
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one aspect you might have missed about Drag tires, and Big drag tires at that is that they act as a clutch and take the initial shock of the driveline locking up and slowly transfer it to the ground to avoid spinning.
the driver is also a key factor here.....you have different reaction times and also sometimes you wheelspin more.....you need to repeat this test with an automatic car so all settings are default in each run
Loving the series idea. I wonder what a 2nd run at 30 would have given since that time ended up being a noticeable outlier. Is there something you can do (in a hatch/estate) with ballast to see how moving the weight distribution around affects the car? Maybe 100kg (water tank?) in the passenger seat, boot and somehow strapped out the front like an Audi engine! ☺
You'd need to do that with a car which can spin the tires up to 3rd gear. Otherwise, you're within the margin of error, because 2 seconds into the run, you can't spin the tires anymore.
On cold road tires there's very little change in traction with higher pressure, they aren't so sensitive. Was interesting to see lowering pressure did give quite a result.
Brilliant video bar one thing. You should have done 3 races for each tyre pressure as launches can vary so an average would have been better. Class video tho!
You should maybe do more runs for 1 tyre pressure to take some stats and draw a graf. Would be very interesting. Beside that, very nice video again. Keep it up 👌
You should have kept the tyre pressure in the front constant. Lower pressure in the front will just increase drag. The lower pressure might actually have been better if it was just the rear wheels.
I experimented a bit with this during my hillclimb/sprint days. Not specifically for launches but for overall handling. Too low pressure and there was a risk the tyre could come off the rim during heavy cornering. Sweet spot for the 13" tyres I used was around 23/24 psi
Contact patch decreases when either over inflated or under inflated, ideal traction would be whatever pressure gives full contact for the weight on the tire.
The lower the tires pressure, the higher the rolling resistance. So yes, you might get a better launch out of it (as seen in the video), however on the long run too low of a pressure will cost you time since the rolling resistance is drastically increased. On a 5000+ hp Dragster that won't be a problem since the centrifugal force pushes the tires outwards thereby creating a smooth surface with less rolling resistance. However actual dragslicks aren't even real tires. They're more like plastic bags (atleast that's what they feel like). They feel like the foil you use to build a nature pool. Normal tires on a normal car will never be able to eleminate the rolling resistance effect and thereby running low pressure is useless and outright dangerous (especially at medium to high cornering speeds)
I have said this many times watching drag races. Letting tyre pressure out made sense decades ago. Cross ply tyres would increase their contact patch when run low. Radial tires we use now not only bulge at the side wall which increases rolling resistance and lateral wash. The tread section collapses inwards reducing the contact patch, limiting grip. Now there is a point to be made that pressure is measured cold and then tires are spun up to make the rubber sticky. This addition of heat will cause the pressure to rise. Which will cause the tread section to bulge ( reduce contact reduce grip ) but this will only account for a couple psi. not dropping 15-25 as I have seen some people doin, surely.
Still plenty of gains to be had on modern radial tires finding the right pressure. The time slips don't lie and anyone bothering to keep track of the tire pressures at the strip probably has enough slips to know what helps their car and doesn't. These lads are hopeless. For me I don't see any gain going bellow 25psi on my street tires at the strip. These crazy low pressures these guys are testing are a bit off the chart for the tires they have I'm sure.
I think the recommended tyre pressure for the Esprit S3 at the front (on 195/60s) is just 22psi. With 205/50 Toyos I used them between 20 and 22psi, so low pressures aren't out of the question. The lower you went with the Esprit, the more pointy the car became. Not so much as it had implications for the rear but I felt you lost some of the gentle subtlety of its beautifully weighted steering. Unfortunately I never did this with the original Goodyear tyres (which aren't made any more) as they were a far better place to start from. I can tell you, though, that Tyrrell raced the 021 and 022 at 17psi, which was lower than most people went back then. That was on Goodyears.
Those numbers are completely academic without knowing if they were measured hot or cold. When tires are used hard they will increase pressure. So for track use you allow for that when setting cold pressures. They will be lower, then when you use them, pressures will increase to the actual desired fastest pressures. That's why you often see tire engineers measuring the temps on a few points across the tire thread right after the car comes back into the pits. This data will be used for setting the pressures on the next set of tires.
For the next video, maybe you guys can test which is faster around the track - understeery car or oversteery car. I know every driver is different but would be a cool test.
need to mess with tire pressures on driven vs driven wheels, now. Low pressure on driven wheels (maybe start at 10, which seemed to be the fastest time you had) for traction, and high pressure on the non-driven wheels (50, 70, etc) to reduce rolling resistance.
High pressure tires can lower the rolling fiction, positively improving acceleration until traction becomes the limiting factor. 65r sidewall are an intelligent balance of rotating mass, comfort and traction for normal road use.. even as consumers and manufacturers aspire to 40 inch rims with 10mm sidewall lol
Yes I totally agree and that’s exactly what I was thinking as well. It’s not convenient to lower the tire pressure to 15-20 psi if the car doesn’t have enough power to grip well to the ground. So the times are not really going to differ. If this was a 500-700hp car you can probably conclude that the tire pressure being lower is actually better
It seemed like you were getting the launch nailed as you did more iterations; I would have liked to have seen a run at 30 psi after doing all the other runs to see if that 10.6 had come down any
Tyre grip is also heavily affected by heat as well. To make this a fair test, the tyres should have been given a significant amount of time to cool down after each run.
Perfect timing. Drove to the shop on flats (thanks neighbors for throwing metal scrap in the driveway). Made it with no rim damage even tho tire was tore all around at the edge of the rim
So often you see people run on 10psi without noticing a thing. It baffles me. I once had one tire go down to 25psi where the rest was around 35 and I immediately noticed one corner of the car becoming wallowy over bumps. Interesting test!
WoW, no one has thought to mention this, lowering tire pressure effectively lowers the final “GEAR RATIO” lower gears will get you off the line faster but flat tires will slow you as you try to go fast.
test 2 off road vehicles. One with big fat wide tyres versus tall skinny tyres. Which one is faster over mud, sand, snow? A lot of off roaders fit big fat wide tyres but most of the time, a tall skinny tyre is actually better over most surfaces but they don't look as cool.
At very low pressure the extra friction kills the performance as the engine has only so much power, but if you run huge horsepower numbers, the loss from friction is pointless on the front of the traction gains.
2:40 on some cars u can see when they do burnout to warm up the tires they expand a little from the heat, also they give some flex on the launch so the power isnt too snappy since that will cause the axel to snap. so there is lots that is happening with low pressure but most simple answer is: more grip
What you say in 2:10 is a very common misconception on why fast cars have wider tires. Actually, smaller surface touching the road means better grip. Distributing the same weight in smaller area increases the grip, it doesn't lower it. That's why, for example, stilts end on a small surface touching the ground and not in a shoe size area. Bigger area would mean that stilts could slip on the ground easier as they would distribute the same weight in a larger area. If you want something to grip on the ground, generally, you make it pointy. Now the problem with all that, is that cars are powerful beasts, and if you try to maximize the grip by lowering the contact area, that tire would be destroyed in a couple of spins or breaks, as the good grip would mean extremely fast wear. So, it's a balance. You have to make the tires thin enough for better grip and wide enough to avoid super fast wear. And that's why it's super stupid to put wider tires in cars that are not powerful, you actually lose grip for no reason at all (except maybe tires that don't grip and last a century).
Sweeeeet. Scott from Driver61 channel. Awesome awesome Guy. Learned a lot from him about Sim-Racing. I give him ALL the credit for the strides I've made. How quick I am. All do to him. Cheers Scott.
most of the difference between 30, 50 and 70 psi is your ability to properly drag-race it: the moment of shifting, speed of the shifts. those matter more than the minimal difference in tire response at fully inflated and over.
This video fulfils a weird childhood dream or nightmare I had, influenced by my parents watching some film where some guy kept ramming their car into something until the logo thing in the middle of the wheel popped off and the tyre went flat.
Championship driver calls his F1 Champion dad for advice. :D I really like this channel. And you could run 70 PSI in those road tires no prob for a few runs, I imagine that burst pressure for a tire like that would be well over 150 psi. Wouldn't do it in hot weather on hot pavement of course.
I used to let the tyres down on my front wheel drive Montego Turbo, it works, it stopped it from wheel spinning and i got more traction.. my mate told me to do it and I thought he was joking, I was so surprised it worked!
two competing forces. for the launch you want traction and more surface area on the tarmac. Once moving, the higher pressure and smaller contact patch cause less friction and therefore more efficient acceleration. The different pressures will produce different advantages and disadvantages at different stages of the 1/8.
I think the issue here more or less is the low profile tire and lack of power to spin in second and third. on a 32" drag tire, we run about 5 PSI, but it's beadlocked so that it wont spin on the rim, and there's a lot more sidewall to stop the wheel hitting the ground or cutting through the tire at all. this helps us keep wheelspin down when the car comes onto boost in third
should've done 3 passes at each PSI and taken the average of each. The first pass was probably slower than the higher psi ones because the driver was rusty, Id imagine each launch gets better than the last one for the most part.
Instead of average, you want the best time. Your best time is limited by what the vehicle can achieve, whereas anything less than that will be uncontrolled factors like the human driver or changes in wind and temperature. Averaging makes sense for distributions where fluctuations can make things better or worse, but when fluctuations can only make things worse than ideal, it's more appropriate to take the best rather than the average (or use something like the geometric mean instead of the arithmetic mean, assuming a log-normal distribution instead of a normal).
u guys forgot one very important detail in this test: u allways used the same set of tires, wich was losing thread at every launch. I'm sure that if u run the latest tests again on new rubber that could make a difference; surely not much, but u guys know how it goes in racing where every bleep of a second counts. ;) Tc guys and keep up the good work.
I love how you just wont do the same test more than once, which would be very important cause a lot can change by the driver doing something a bit different
Lower TIRE pressure increases surface area of the tire. That can be both good and bad. When accelerating, that extra surface area can help but at high speeds it slows you down. The optimal system would be able to change tire pressure on the road between accelerating and increase as speed increases for less friction. Then drop slightly for braking and cornering.
In a dragster, the best accelerration is achieved when wheelspin is about 15%. That is certainly related to the tyres air pressure and raw power spinning those tyres. The number (wheelspin %) might be outdated, I learned that many years ago, but the principle is probably still the same, the best acceleration includes also some carefully tuned wheelspinning during the run.
Could be that the lower pressure allows better traction off the line but higher rolling resistance once moving hense the sweet spot. After that test I wouldn't use those tyres again.
On those ultra-low pressures, the rolling resistance will be considerably increased, so any advantage off the lines will be negated by a slower top speed. I should add that (very roughly speaking), the contact area is in inverse proportion to the tyre pressure. Double the pressure and it halves the contact area. That's because, to a rough approximation, the weight carried by the tyre is the internal pressure multiplied by the contact area. So, if the tyre is supporting, say, 500 pounds and there's 50 psi then there's a 10 square inch contact area. At 25 psi it would be 20 square inches. I say it's rough, because that calculation ignores the weight carried by the side walls and tyres are not balloons - they have some compressive strength in the tyre walls through the construction. On this particular set of tests then I doubt it proves too much. That Mazda doesn't exactly have a great deal of excessive power to break the tyres loose under acceleration, and if the tyres are not allowed to cool down between runs (which, being rubber, isn't quick), then there will be some effect from that. It would take several runs at each pressure to eliminate driver variables; even in F1 the drivers aren't completely consistent in their starts, albeit they have a huge excess of power over traction to deal with.
Have you considered the long-term damage you have done to the tyre structure with those heat inputs? Don't be amazed if they let go when you're motorway cruising or, worse still, pushing the car hard through some complex bend with a long drop over one side? Sayonara!
Haven't finished the video but so far, no trap speeds? Might get worse launch but maybe a power limited car such as is used in the video, can gain it back in the remainder of the eight?
I picked up a bolt once on my back right that made it go flat, couldn't feel it no idea how long I was driving on a flat but eventually I started smelling burning rubber at a couple stop lights that made me check my tires and sure enough it was flat and the side walls were shredded, good thing I had a donut to swap, I keep seeing all these new cars coming with fix-a-kits instead of a spare, and that would have left me stranded.
I air my tires down for more grip while drifting. That way we can chunk the car into the turn faster without spinning out or going off track. I’ve had mine under 10psi. Crazy seeing the entire sidewall worn down at the end of a track day lol
Drag slicks are bias ply and are specifically designed to run low air pressure, conventional tires will tend to cup upwards in the center reducing the contact patch, making less traction instead of more like a drag slick.
This is an old video and such but I like to show people that I'm smart (cause I'm soooo egocentric) so I'll still write this comment. 8:40 that is incorrect, the fact that the tyre is compressing and going back to its original shape doesn't heat it up, if anything it cools it down. When rubber compresses (as well as when it's stretched) it heats up, this is because of a change in entropy that we are going to avoid talking about. One might think that this is why the tyres heat up, they compress and decompress so fast that they must heat up, right? WRONG. Rubber heats up when compressed, but it cools down to its original temperature when it goes back to its original shape. So there should be no change in temperature, but actually there is, the rubber COOLS DOWN. How tf? When you compress rubber, it increases its temperature because of a change in entropy, but its overall energy is the same, now that the tyre is hotter than the surrounding air, it will start exchanging heat with it, so therefore it will lose energy, now both the air and the tyre are at 25 celsius, but when decompressing the tyre, the change in its entropy will cause a drop in temperature, and therefore, the rubber will cool down. TL;DR: The tyre doesn't heat up because it's being compressed and decompressed too many times, as stated in minute 8:40. EDIT: I know that a change in entropy does mean a change in energy but I wanted to avoid talking about entropy as it's a topic I am not proficient at.
At launch I am sure you get better traction therefore more speed. I have a 2004 Jeep Wrangler Rubi with ARB lockers 4:56 grears and I run at 4 PSI to rock crawl.
low power engines like to have some wheelspin to get higher rpm at launch. many people used to put slicks on their car long before they were needed, and the car would bog off the line.
My .02c, if you wanted to go quicker with the insanely low pressures you need to then remove the wheelspin. It sounded like at the 20psi and lower mark you were revving the engine higher which I don't think helped put at 5psi. At 5 you needed to back off the throttle just a touch to allow it to actually grab and then hammer it on. Any drag racer will tell you that you need to hook up to go quick, but they're still able to do burnouts and also ruin races by breaking loose off the line. No need for a retest because obv it's not sade to be that low at high speed on street tires but I bet if you backed off the launch and then hammered it immediately after hooking up you'd see a tiny but consistent improvement possible.
There was once a fifth gear drag race in double decker buses and he said he had a worst start because his door was open Always wondered would a car with windows and windscreen be faster than a car with no windows or windscreen but with ballast to be the same spec. Windscreen is more aero but no windscreen is less surface area
Really cool idea, but FOR SCIENCE I would you to do again with something like an automatic Mustang V8 - widely available, cheap to fool around in, enough power to really challenge traction, repeatable and little weight over the rear wheels.
4:30 I'm not sure if the gear ratio actually changes when the wheels are compressed: The circumference of the tire stays the same, so the wheel still travels the same distance per revolution, which means that the gear ratio should stay the same if I'm not mistaken.
the center of the wheel gets closer to the ground. the lever is shorter. it gives it "more gear". the circumference of the tire means nothing. what matters is the distance from the axle center to the ground.
actually new cars with ABS sensors judge whether the tire is going flat by measuring the relative rotation, and leaking tires start to show a different effective circumference which throws a signal.
So in drifting, if the car is plowing the front end into the corner, they will increase rear, and lower the front tire pressure. It can be a final tuning aid for sure.
You should do a fun competition with the Donut Media team! Some sort of cross pond rivalry on a fun experiment build like one where the teams can only spend x amount of money and have to meet some performance goal. Keep it up, y’all are doing great!
The problem is as the pressure gets too low the middle of the tire is lifted from the ground and the side squished to the ground if looking at the wheel from the front or rear not the side you will see the dip in the middle of the tire and the edged raised... its the opposite if too much air the middle will be raised and sides lower, there is a sweet spot and that is the pressure on the sidewall unless its a drag radial
Aktuwully... You drive on the volume of air inside of the tyre - not the pressure. Giant drag tyres and truck tyres have a huge volume so don't need as much pressure for the same weight, skinny road tyres will need a higher pressure because of their smaller cross section than beefy tyres. IE, if you double the volume of a tyre the optimal pressure will be halved
Although entertaining, this test has too many variables like driver input, tire temperature and rolling resistance over the length of the run, to name a few. Besides, drifters have the tire pressure to grip relationship pretty well figured out (independent of drag racers). 👍
A bit like suspension stiffness i think it s a balance to find between grip and "stability". as the tires are softer, the torsion of the sidewalls adds some coeff of friction, but too soft and the bad "stability" of the tyre makes the power having more difficulties to pass. But yeah tyres are still some black magic. Funny video.
It kinda transfers over but no at extremely low PSI’s plus you have to heat the tires with a burnout with you at really low air pressure we run 5-10psi *( we use what’s called bead lock to keep the wheel from spinning on the rim which is bolting the tire to the rim )* in our slicks we can’t below 5psi it’s a mandated rule you can put as much in as you want but no more than 10 is optimal and it depends on track temp and air temp on what pressure you run I was usually between 5-8 psi on a 14” wide bias ply slick I ran a 383cid small block Chevy making about 1k HP N/A the I had a 500HP nitrous kit as well which I used from line to line dragsters only run around 8 psi in there slicks as well the lowest they can go is also 5 psi which allow the tires to stand which changes the gear ratio making the car faster and that’s why we run such low pressures they help us launch better and go faster and that wobble you talked about we get that at the end of the track because we’re running bias ply rears and radial fronts at 45psi for a better reaction time
I’d love to see how low you can go doing track driving before the bead gives up. Doing off-road stuff 10psi is about as low as I ever dare go before I get too worried about blowing the bead Without bead locks but I’ve heard some guys go even lower
Those flat tyres were sketchy!! What would you like us to test next??
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I remember a motorbike magazine did a cool test about 15yrs back. They covered over the speedometer on a bike and got three different riders to go along a runway at whatever they thought was 30, 50, 60, 70 & 100mph. Of the three the guy who was a speed freak was actually the most accurate, while the worst was a copper! Could be a cool test to try, especially if you used a big comfy car vs the mx5!
explain about promod car please i subscribed
How about driving a circular track always on the inside lane and then driving it always on the outermost Lane and comparing the times.
What would happen to different types of race cars if they encountered a pothole? Even on street circuits, this has to be an extremely rare occurrence for today’s race car drivers
15 psi is the best pressure to contact patch ratio. Because any lower will actually decrease your contact patch as the tyre tends to fold in and you have what it's called "shoulder wear", when central part of the tyre is actually lifted off the contact surface and you are running on the two edges. It's quite easily identifiable just by looking at how they were worn out.
Plus, the most important part of it is the make of tyres itself. And I'm not talking about brand, but what they're made off. Some tyres could be were hard composition of rubber, some will be very very soft. From my own experience the softest tyre I've ever had on my car was Michelin Eco tyre, I don't remember exact model name, but that tyre was so soft lightweight and flexible that I was able to turn it *inside out* and that shocked me.
Use a car with power where the tires matter more, and launch control to eliminate the driver variable
That's basically what Adam said
@@joedee6630 Believe in JESUS today, confess and repent of your sins. No one goes to heaven for doing good but by believing in JESUS who died for our sins. GOD loves you soo much unconditionally.🤩❤😍🤗😇☺🙏
@@alunesh12345 i like men
@@Fred_the_1996 lol
@@alunesh12345 bruh what is this, the crusades? You really just be going around preaching this shit? 💀💀
Would love to see how those tire pressures handle a corner close up and braking/lap time.
Yes!!!
I already know that a flat tire makes my car faster...going sideways in a curve.
And more power
They would debead
@@levibazen608 this guy understands. Came to this thread looking for this comment
The ideal pressure depends on the size of the tire (and of course on the car it is fitted to and especially its weight). It doesn't really make sense to compare tirepressures between tires of different sizes or between different cars.
Yup pressure in the door is with factory tire in mind
Obviously you wouldn’t want 20psi on a karting tyre, you would finish last by farrrrrr 👍
Its like comparing a mountain bike tyre with a road bike tyre lol
@@johndc2998 Believe in JESUS today, confess and repent of your sins. No one goes to heaven for doing good but by believing in JESUS who died for our sins. GOD loves you soo much unconditionally.🤩❤😍🤗😇☺🙏
Well for science reasons they did this anyways, because science is fun. (Just pretend there's no math included for right now)
Would be super interesting to see how these pressures would affect a laptime or cornering ability
Yes, but actually no. At a certain point it will just come off the bead, so very dangerous
@@kbwthor1405 Believe in JESUS today, confess and repent of your sins. No one goes to heaven for doing good but by believing in JESUS who died for our sins. GOD loves you soo much unconditionally.🤩❤😍🤗😇☺🙏
Indeed. In my old NB MX5 book pressure was about 26-28spi but autocross guys will run up to 36psi.
its getting worse
Experiment would have been better with a vehicle that actually had enough horsepower to spin the tires.
He dumped the clutch at 50 psi and got some decent spin. The other launches were bogged down.
@@fivespeed3026 Believe in JESUS today, confess and repent of your sins. No one goes to heaven for doing good but by believing in JESUS who died for our sins. GOD loves you soo much unconditionally.🤩❤😍🤗😇☺🙏
@@alunesh12345
@@alunesh12345 no
@@alunesh12345 hail Satan
I should have known Brit's measure heat in relation to tea.
@6:40 not sure the gains are even real. you had to try twice. i think rolling resistance is just as important for such a low power car when doing this, and high pressure has the advantage there, even with only the rear tires being pumped. pump all four tires to 50 psi and you'd have your best time, specially in 1/4 mile or longer runs.
True. The car has barely power to spin 1st gear. Its like a bicycle that runs easier with pumped tyres...
Miata will spin 3rd stock man. They aren't powerful. But they are also light and have a suspension designed for corners, not drag launches.
How much drag racing have you done?
I hope you let the tyres cool down in between. Temps of the tyers also has an effect.
I was wondering if cold tyres were the reason the 30 PSI test gave the worst result...
8:36 yep that happend here
They didn't even do multiple runs and average the results; of course they didn't let the tires cool down first.
I had a MR2 with ultra low profiles and got a flat rear tire, the sidewall was so stiff that I couldn't even feel the flat below 30mph! Drove all the way to the local asda and shredded the sidewall! 🤣🤣
And you’re laughing?
@@justkev1044 yeah of course, no one was hurt and it was an easy fix! Gotta laugh about these little things!
Believe in JESUS today, confess and repent of your sins. No one goes to heaven for doing good but by believing in JESUS who died for our sins. GOD loves you soo much unconditionally.🤩❤😍🤗😇☺🙏
@@alunesh12345 I can do donuts in my Miata! Can your Jesus do that?
@@dylanboyd6147 yes.
one aspect you might have missed about Drag tires, and Big drag tires at that is that they act as a clutch and take the initial shock of the driveline locking up and slowly transfer it to the ground to avoid spinning.
Nice
I didn't know that
Just learned something new
Thanks
Hamilton is typing...
the driver is also a key factor here.....you have different reaction times and also sometimes you wheelspin more.....you need to repeat this test with an automatic car so all settings are default in each run
I loved seeing the tire wrinkle at 5 PSI! That was awesome!
Loving the series idea. I wonder what a 2nd run at 30 would have given since that time ended up being a noticeable outlier.
Is there something you can do (in a hatch/estate) with ballast to see how moving the weight distribution around affects the car? Maybe 100kg (water tank?) in the passenger seat, boot and somehow strapped out the front like an Audi engine! ☺
MASSIVE thumbs up for this youtuber that goes straight into action within 30s of video instead of warbling aroung
You'd need to do that with a car which can spin the tires up to 3rd gear. Otherwise, you're within the margin of error, because 2 seconds into the run, you can't spin the tires anymore.
are flat tires safe to race out?🤔
@@raven4k998 I'd say going 335 mph on 2.5 in wide tires isn't, but then top fuel dragsters exist...
@@EddieOtoolnot to mention tires heat up so while driving you should still keep the bead below recommended psi
On cold road tires there's very little change in traction with higher pressure, they aren't so sensitive. Was interesting to see lowering pressure did give quite a result.
Brilliant video bar one thing. You should have done 3 races for each tyre pressure as launches can vary so an average would have been better. Class video tho!
You should maybe do more runs for 1 tyre pressure to take some stats and draw a graf. Would be very interesting. Beside that, very nice video again. Keep it up 👌
You should have kept the tyre pressure in the front constant. Lower pressure in the front will just increase drag. The lower pressure might actually have been better if it was just the rear wheels.
I experimented a bit with this during my hillclimb/sprint days. Not specifically for launches but for overall handling. Too low pressure and there was a risk the tyre could come off the rim during heavy cornering. Sweet spot for the 13" tyres I used was around 23/24 psi
instead of acceleration you could test tyre pressure vs cornering speed or lateral 💫G-force
Contact patch decreases when either over inflated or under inflated, ideal traction would be whatever pressure gives full contact for the weight on the tire.
After their 15psi, you can see the wheel hub spinning before the rubber does which means the rubber is slipping.
The lower the tires pressure, the higher the rolling resistance. So yes, you might get a better launch out of it (as seen in the video), however on the long run too low of a pressure will cost you time since the rolling resistance is drastically increased. On a 5000+ hp Dragster that won't be a problem since the centrifugal force pushes the tires outwards thereby creating a smooth surface with less rolling resistance. However actual dragslicks aren't even real tires. They're more like plastic bags (atleast that's what they feel like). They feel like the foil you use to build a nature pool. Normal tires on a normal car will never be able to eleminate the rolling resistance effect and thereby running low pressure is useless and outright dangerous (especially at medium to high cornering speeds)
I have said this many times watching drag races. Letting tyre pressure out made sense decades ago. Cross ply tyres would increase their contact patch when run low. Radial tires we use now not only bulge at the side wall which increases rolling resistance and lateral wash. The tread section collapses inwards reducing the contact patch, limiting grip. Now there is a point to be made that pressure is measured cold and then tires are spun up to make the rubber sticky. This addition of heat will cause the pressure to rise. Which will cause the tread section to bulge ( reduce contact reduce grip ) but this will only account for a couple psi. not dropping 15-25 as I have seen some people doin, surely.
Still plenty of gains to be had on modern radial tires finding the right pressure. The time slips don't lie and anyone bothering to keep track of the tire pressures at the strip probably has enough slips to know what helps their car and doesn't. These lads are hopeless. For me I don't see any gain going bellow 25psi on my street tires at the strip. These crazy low pressures these guys are testing are a bit off the chart for the tires they have I'm sure.
I think the recommended tyre pressure for the Esprit S3 at the front (on 195/60s) is just 22psi. With 205/50 Toyos I used them between 20 and 22psi, so low pressures aren't out of the question. The lower you went with the Esprit, the more pointy the car became. Not so much as it had implications for the rear but I felt you lost some of the gentle subtlety of its beautifully weighted steering. Unfortunately I never did this with the original Goodyear tyres (which aren't made any more) as they were a far better place to start from. I can tell you, though, that Tyrrell raced the 021 and 022 at 17psi, which was lower than most people went back then. That was on Goodyears.
Those numbers are completely academic without knowing if they were measured hot or cold.
When tires are used hard they will increase pressure. So for track use you allow for that when setting cold pressures. They will be lower, then when you use them, pressures will increase to the actual desired fastest pressures.
That's why you often see tire engineers measuring the temps on a few points across the tire thread right after the car comes back into the pits. This data will be used for setting the pressures on the next set of tires.
@@jfv65 Thank you for that lesson. I'm always happy to learn more about suspension dynamics, especially on racing cars.
For the next video, maybe you guys can test which is faster around the track - understeery car or oversteery car. I know every driver is different but would be a cool test.
need to mess with tire pressures on driven vs driven wheels, now. Low pressure on driven wheels (maybe start at 10, which seemed to be the fastest time you had) for traction, and high pressure on the non-driven wheels (50, 70, etc) to reduce rolling resistance.
High pressure tires can lower the rolling fiction, positively improving acceleration until traction becomes the limiting factor.
65r sidewall are an intelligent balance of rotating mass, comfort and traction for normal road use.. even as consumers and manufacturers aspire to 40 inch rims with 10mm sidewall lol
Yes I totally agree and that’s exactly what I was thinking as well. It’s not convenient to lower the tire pressure to 15-20 psi if the car doesn’t have enough power to grip well to the ground. So the times are not really going to differ. If this was a 500-700hp car you can probably conclude that the tire pressure being lower is actually better
It seemed like you were getting the launch nailed as you did more iterations; I would have liked to have seen a run at 30 psi after doing all the other runs to see if that 10.6 had come down any
Very entertaining science, I'd use an automatic car since it's more consistent to see if there's really any benefit!
Tyre grip is also heavily affected by heat as well. To make this a fair test, the tyres should have been given a significant amount of time to cool down after each run.
Perfect timing. Drove to the shop on flats (thanks neighbors for throwing metal scrap in the driveway). Made it with no rim damage even tho tire was tore all around at the edge of the rim
So often you see people run on 10psi without noticing a thing. It baffles me. I once had one tire go down to 25psi where the rest was around 35 and I immediately noticed one corner of the car becoming wallowy over bumps. Interesting test!
WoW, no one has thought to mention this, lowering tire pressure effectively lowers the final “GEAR RATIO” lower gears will get you off the line faster but flat tires will slow you as you try to go fast.
test 2 off road vehicles. One with big fat wide tyres versus tall skinny tyres. Which one is faster over mud, sand, snow? A lot of off roaders fit big fat wide tyres but most of the time, a tall skinny tyre is actually better over most surfaces but they don't look as cool.
At very low pressure the extra friction kills the performance as the engine has only so much power, but if you run huge horsepower numbers, the loss from friction is pointless on the front of the traction gains.
2:40 on some cars u can see when they do burnout to warm up the tires they expand a little from the heat, also they give some flex on the launch so the power isnt too snappy since that will cause the axel to snap. so there is lots that is happening with low pressure but most simple answer is: more grip
10:28 if you don't want to watch the whole video
What you say in 2:10 is a very common misconception on why fast cars have wider tires. Actually, smaller surface touching the road means better grip. Distributing the same weight in smaller area increases the grip, it doesn't lower it. That's why, for example, stilts end on a small surface touching the ground and not in a shoe size area. Bigger area would mean that stilts could slip on the ground easier as they would distribute the same weight in a larger area. If you want something to grip on the ground, generally, you make it pointy.
Now the problem with all that, is that cars are powerful beasts, and if you try to maximize the grip by lowering the contact area, that tire would be destroyed in a couple of spins or breaks, as the good grip would mean extremely fast wear. So, it's a balance. You have to make the tires thin enough for better grip and wide enough to avoid super fast wear.
And that's why it's super stupid to put wider tires in cars that are not powerful, you actually lose grip for no reason at all (except maybe tires that don't grip and last a century).
Should have checked the temperature of the tires in between runs...the more the car runs, the more friction the more heat equals sticker tires
Dragster tyres are bolted so are directly connected to the rim. On the Mazda the rim and tyre will slip as you are relying on the bead.
Yes and he could have marked the rim/tire to see if slippage had occurred.
YOU GUYS NEED MORE SUBS! THANKS FOR THE INFORMATIONAL VIDEO :))
On a car with minimal power like that, I can imagine the drag at speed could cancel out the gains at initial launch.
“you alright scott?” subtle but heartwarming
Sweeeeet. Scott from Driver61 channel. Awesome awesome Guy. Learned a lot from him about Sim-Racing. I give him ALL the credit for the strides I've made. How quick I am. All do to him. Cheers Scott.
most of the difference between 30, 50 and 70 psi is your ability to properly drag-race it: the moment of shifting, speed of the shifts. those matter more than the minimal difference in tire response at fully inflated and over.
This video fulfils a weird childhood dream or nightmare I had, influenced by my parents watching some film where some guy kept ramming their car into something until the logo thing in the middle of the wheel popped off and the tyre went flat.
Great video but you should try the same on a more powerful car than this, because the mx-5 just doesn't have enough power.
Championship driver calls his F1 Champion dad for advice. :D
I really like this channel. And you could run 70 PSI in those road tires no prob for a few runs, I imagine that burst pressure for a tire like that would be well over 150 psi.
Wouldn't do it in hot weather on hot pavement of course.
I used to let the tyres down on my front wheel drive Montego Turbo, it works, it stopped it from wheel spinning and i got more traction.. my mate told me to do it and I thought he was joking, I was so surprised it worked!
two competing forces. for the launch you want traction and more surface area on the tarmac. Once moving, the higher pressure and smaller contact patch cause less friction and therefore more efficient acceleration. The different pressures will produce different advantages and disadvantages at different stages of the 1/8.
I think the issue here more or less is the low profile tire and lack of power to spin in second and third. on a 32" drag tire, we run about 5 PSI, but it's beadlocked so that it wont spin on the rim, and there's a lot more sidewall to stop the wheel hitting the ground or cutting through the tire at all. this helps us keep wheelspin down when the car comes onto boost in third
should've done 3 passes at each PSI and taken the average of each. The first pass was probably slower than the higher psi ones because the driver was rusty, Id imagine each launch gets better than the last one for the most part.
He is a race car driver
@@jeyoung6244 I didn't know that but still, his performance would get better with each run and averages would be more accurate :)
Instead of average, you want the best time. Your best time is limited by what the vehicle can achieve, whereas anything less than that will be uncontrolled factors like the human driver or changes in wind and temperature. Averaging makes sense for distributions where fluctuations can make things better or worse, but when fluctuations can only make things worse than ideal, it's more appropriate to take the best rather than the average (or use something like the geometric mean instead of the arithmetic mean, assuming a log-normal distribution instead of a normal).
@@reverse_engineered that's actually a really good point, still means more tests were needed.
u guys forgot one very important detail in this test: u allways used the same set of tires, wich was losing thread at every launch. I'm sure that if u run the latest tests again on new rubber that could make a difference; surely not much, but u guys know how it goes in racing where every bleep of a second counts. ;)
Tc guys and keep up the good work.
I love how you just wont do the same test more than once, which would be very important cause a lot can change by the driver doing something a bit different
Thank you for your show, I really enjoy them. Perhaps you could make one about track conditions and tyre pressures? Thanks again
Lower TIRE pressure increases surface area of the tire. That can be both good and bad. When accelerating, that extra surface area can help but at high speeds it slows you down. The optimal system would be able to change tire pressure on the road between accelerating and increase as speed increases for less friction. Then drop slightly for braking and cornering.
Would be cool to check the difference between heavier and lighter wheels. Suppose the higher rotational mass would be slower, but by how much?
In a dragster, the best accelerration is achieved when wheelspin is about 15%. That is certainly related to the tyres air pressure and raw power spinning those tyres. The number (wheelspin %) might be outdated, I learned that many years ago, but the principle is probably still the same, the best acceleration includes also some carefully tuned wheelspinning during the run.
Could be that the lower pressure allows better traction off the line but higher rolling resistance once moving hense the sweet spot. After that test I wouldn't use those tyres again.
On those ultra-low pressures, the rolling resistance will be considerably increased, so any advantage off the lines will be negated by a slower top speed. I should add that (very roughly speaking), the contact area is in inverse proportion to the tyre pressure. Double the pressure and it halves the contact area. That's because, to a rough approximation, the weight carried by the tyre is the internal pressure multiplied by the contact area. So, if the tyre is supporting, say, 500 pounds and there's 50 psi then there's a 10 square inch contact area. At 25 psi it would be 20 square inches. I say it's rough, because that calculation ignores the weight carried by the side walls and tyres are not balloons - they have some compressive strength in the tyre walls through the construction.
On this particular set of tests then I doubt it proves too much. That Mazda doesn't exactly have a great deal of excessive power to break the tyres loose under acceleration, and if the tyres are not allowed to cool down between runs (which, being rubber, isn't quick), then there will be some effect from that. It would take several runs at each pressure to eliminate driver variables; even in F1 the drivers aren't completely consistent in their starts, albeit they have a huge excess of power over traction to deal with.
Have you considered the long-term damage you have done to the tyre structure with those heat inputs? Don't be amazed if they let go when you're motorway cruising or, worse still, pushing the car hard through some complex bend with a long drop over one side? Sayonara!
Haven't finished the video but so far, no trap speeds? Might get worse launch but maybe a power limited car such as is used in the video, can gain it back in the remainder of the eight?
I picked up a bolt once on my back right that made it go flat, couldn't feel it no idea how long I was driving on a flat but eventually I started smelling burning rubber at a couple stop lights that made me check my tires and sure enough it was flat and the side walls were shredded, good thing I had a donut to swap, I keep seeing all these new cars coming with fix-a-kits instead of a spare, and that would have left me stranded.
I air my tires down for more grip while drifting. That way we can chunk the car into the turn faster without spinning out or going off track. I’ve had mine under 10psi. Crazy seeing the entire sidewall worn down at the end of a track day lol
Drag slicks are bias ply and are specifically designed to run low air pressure, conventional tires will tend to cup upwards in the center reducing the contact patch, making less traction instead of more like a drag slick.
This is an old video and such but I like to show people that I'm smart (cause I'm soooo egocentric) so I'll still write this comment.
8:40 that is incorrect, the fact that the tyre is compressing and going back to its original shape doesn't heat it up, if anything it cools it down. When rubber compresses (as well as when it's stretched) it heats up, this is because of a change in entropy that we are going to avoid talking about. One might think that this is why the tyres heat up, they compress and decompress so fast that they must heat up, right? WRONG. Rubber heats up when compressed, but it cools down to its original temperature when it goes back to its original shape. So there should be no change in temperature, but actually there is, the rubber COOLS DOWN. How tf?
When you compress rubber, it increases its temperature because of a change in entropy, but its overall energy is the same, now that the tyre is hotter than the surrounding air, it will start exchanging heat with it, so therefore it will lose energy, now both the air and the tyre are at 25 celsius, but when decompressing the tyre, the change in its entropy will cause a drop in temperature, and therefore, the rubber will cool down.
TL;DR: The tyre doesn't heat up because it's being compressed and decompressed too many times, as stated in minute 8:40.
EDIT: I know that a change in entropy does mean a change in energy but I wanted to avoid talking about entropy as it's a topic I am not proficient at.
At launch I am sure you get better traction therefore more speed. I have a 2004 Jeep Wrangler Rubi with ARB lockers 4:56 grears and I run at 4 PSI to rock crawl.
its more about having right amount of spin to dig faster, i think on this low power more psi is better ;D
low power engines like to have some wheelspin to get higher rpm at launch. many people used to put slicks on their car long before they were needed, and the car would bog off the line.
@@mustang351c4 it doesnt wheel spin, doesnt make torque/power. stops spinning at low rpm ;D
My .02c, if you wanted to go quicker with the insanely low pressures you need to then remove the wheelspin. It sounded like at the 20psi and lower mark you were revving the engine higher which I don't think helped put at 5psi. At 5 you needed to back off the throttle just a touch to allow it to actually grab and then hammer it on. Any drag racer will tell you that you need to hook up to go quick, but they're still able to do burnouts and also ruin races by breaking loose off the line.
No need for a retest because obv it's not sade to be that low at high speed on street tires but I bet if you backed off the launch and then hammered it immediately after hooking up you'd see a tiny but consistent improvement possible.
raise the front tyre pressures for less rolling resistance, push the car yourself to feel the difference 😉
There was once a fifth gear drag race in double decker buses and he said he had a worst start because his door was open
Always wondered would a car with windows and windscreen be faster than a car with no windows or windscreen but with ballast to be the same spec. Windscreen is more aero but no windscreen is less surface area
Dom torretto: give me a 10 second car
Paul: gives him this beast of a stock miata
Really cool idea, but FOR SCIENCE I would you to do again with something like an automatic Mustang V8 - widely available, cheap to fool around in, enough power to really challenge traction, repeatable and little weight over the rear wheels.
4:30 I'm not sure if the gear ratio actually changes when the wheels are compressed: The circumference of the tire stays the same, so the wheel still travels the same distance per revolution, which means that the gear ratio should stay the same if I'm not mistaken.
the center of the wheel gets closer to the ground. the lever is shorter. it gives it "more gear". the circumference of the tire means nothing. what matters is the distance from the axle center to the ground.
actually new cars with ABS sensors judge whether the tire is going flat by measuring the relative rotation, and leaking tires start to show a different effective circumference which throws a signal.
@@pault151 Yes, I think the circumference changes relative to the tire pressure but that does not contradict my point.
On low profile Street tires, the circumference will be insignificantly different.
Man I love all these new serieses for science. Like and subscribe 👍🏻
To get better traction on rocks or sand, in 4x4 offroad world we sometimes go down to 4-7 PSI pressure.
So in drifting, if the car is plowing the front end into the corner, they will increase rear, and lower the front tire pressure. It can be a final tuning aid for sure.
5psi would make a difference off the line, like 60ft maybe. Later it will be restraining the momentum.
Impressive 10 sec mule though 👌
0:09 are we gonna ignore that cone?
You should do multiple runs on the same pressure, because there will be a lot driver related variation from one drive to another
On dragsters they have beadlocks a rim that grips on the inside of the rim to prevent the tire ripping off. Same as rock crawling 4x4 cars
great channel and fun test
2:55 Perfect!!
You should do a fun competition with the Donut Media team! Some sort of cross pond rivalry on a fun experiment build like one where the teams can only spend x amount of money and have to meet some performance goal. Keep it up, y’all are doing great!
The problem is as the pressure gets too low the middle of the tire is lifted from the ground and the side squished to the ground if looking at the wheel from the front or rear not the side you will see the dip in the middle of the tire and the edged raised... its the opposite if too much air the middle will be raised and sides lower, there is a sweet spot and that is the pressure on the sidewall unless its a drag radial
Haven’t watched the video yet, but I consistently shaved 2 tenths off my quarter mile (13.6 down to 13.4) in a Polo GTI, Michelin PS4 at 14psi
Aktuwully... You drive on the volume of air inside of the tyre - not the pressure. Giant drag tyres and truck tyres have a huge volume so don't need as much pressure for the same weight, skinny road tyres will need a higher pressure because of their smaller cross section than beefy tyres.
IE, if you double the volume of a tyre the optimal pressure will be halved
Although entertaining, this test has too many variables like driver input, tire temperature and rolling resistance over the length of the run, to name a few. Besides, drifters have the tire pressure to grip relationship pretty well figured out (independent of drag racers). 👍
A bit like suspension stiffness i think it s a balance to find between grip and "stability". as the tires are softer, the torsion of the sidewalls adds some coeff of friction, but too soft and the bad "stability" of the tyre makes the power having more difficulties to pass. But yeah tyres are still some black magic. Funny video.
The engineer Callum has the EXACT same voice as Adam from Michael the Producer videos. Uncanny
seeing that makes me wish there were a road track racing series that mandates high sidewalls and low pressures
F1 but with the older tires and 15 psi
OK, setting my Honda CRV to 20 PSI 🏎️
It kinda transfers over but no at extremely low PSI’s plus you have to heat the tires with a burnout with you at really low air pressure we run 5-10psi *( we use what’s called bead lock to keep the wheel from spinning on the rim which is bolting the tire to the rim )* in our slicks we can’t below 5psi it’s a mandated rule you can put as much in as you want but no more than 10 is optimal and it depends on track temp and air temp on what pressure you run I was usually between 5-8 psi on a 14” wide bias ply slick I ran a 383cid small block Chevy making about 1k HP N/A the I had a 500HP nitrous kit as well which I used from line to line dragsters only run around 8 psi in there slicks as well the lowest they can go is also 5 psi which allow the tires to stand which changes the gear ratio making the car faster and that’s why we run such low pressures they help us launch better and go faster and that wobble you talked about we get that at the end of the track because we’re running bias ply rears and radial fronts at 45psi for a better reaction time
Standard English Measuring System: The "Cup of Tea" Index
85-100 °C - fresh out the kettle
45-84°C - ready cup of tea
I’d love to see how low you can go doing track driving before the bead gives up. Doing off-road stuff 10psi is about as low as I ever dare go before I get too worried about blowing the bead Without bead locks but I’ve heard some guys go even lower
6 psi on crazy soft beach sand and some careful turning.