Last year I started running the Bridgestone Potenza RE-11A on my S2000. It offers fantastic grip at the track but I'm still trying to dial in the pressures (they're a little more sensitive to it than the old RE050's were). Assuming a car has 50/50 weight distribution will higher or lower rear tire pressure decrease oversteer? I always thought higher rear pressure did that but I talked to a racer this weekend who thought the opposite.
Track tire pressure - Oversteer/understeer
- Thread starter gofast182
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Higher rear pressure will cause oversteer. That's not what will get you the fastest lap times though.
It depends. If the pressure is too low and you're putting too much weight on tire shoulders, then increasing pressure will increase grip. However, if you're at or above the ideal pressure, increasing pressure will reduce your contact patch and reduce grip.
Originally Posted By: rslifkin
It depends. If the pressure is too low and you're putting too much weight on tire shoulders, then increasing pressure will increase grip. However, if you're at or above the ideal pressure, increasing pressure will reduce your contact patch and reduce grip.
^^^This. If the rear tire contact pattern is going off the tread block, more air pressure is needed. I normally add pressure in 3 psi increments, then do some more laps and see how it feels.
It depends. If the pressure is too low and you're putting too much weight on tire shoulders, then increasing pressure will increase grip. However, if you're at or above the ideal pressure, increasing pressure will reduce your contact patch and reduce grip.
^^^This. If the rear tire contact pattern is going off the tread block, more air pressure is needed. I normally add pressure in 3 psi increments, then do some more laps and see how it feels.
So you want to decrease oversteer? On entry, mid corner, exit? What I would try, is to find a rear pressure that grips best, then tweek the front pressures for balance.(I did the opposite for the fwd neon)
Easier to drive would be to soften the fronts a bit, it would help slow the front end changing directions so the back end doesn't get "tossed" into the corner so hard on entry. If you are already very smooth on the steering, then increasing the front pressures would give better feel but still understeer more mid corner. If you are getting sideways on exits, maybe you jumping on the throttle too hard? A progressive squeeze would put weight onto the back and promote more understeer.
I liked running the rears abit softer on the Neon as it allowed more "toss" on entry and a more gradual breakaway if I over did it.
I imagine with normal alignment the S2000 should be pretty neutral but very responsive to under or oversteering depending on what the driver is doing. Maybe you are telling it to go sideways without knowing it?
Easier to drive would be to soften the fronts a bit, it would help slow the front end changing directions so the back end doesn't get "tossed" into the corner so hard on entry. If you are already very smooth on the steering, then increasing the front pressures would give better feel but still understeer more mid corner. If you are getting sideways on exits, maybe you jumping on the throttle too hard? A progressive squeeze would put weight onto the back and promote more understeer.
I liked running the rears abit softer on the Neon as it allowed more "toss" on entry and a more gradual breakaway if I over did it.
I imagine with normal alignment the S2000 should be pretty neutral but very responsive to under or oversteering depending on what the driver is doing. Maybe you are telling it to go sideways without knowing it?
I'm primarily concerned with mid corner. This way I can carry more speed going in and I can deal with some oversteer on track-out. I do have a tweaked alignment and overall the car is quite neutral and easy to control.
Last Sunday I ran with the rears 2psi higher and overall the car was pretty good. Since it was the first session of the year I left the VSA on and noticed it blink on a few times. The track I was on had a banked bowl/lightbulb turn that was pretty hard on the LF. I want to ease the load on that tire while reducing the tendancy for oversteer mid-corner so I can go faster at turn-in. Again it's not a problem right now, just a desire to find a little more speed, I was running with an E46 M3 who had about .3 (guessing) seconds per lap on me and I felt I could've been right there with him trading places and challenging each other if the tires were dialed in better.
Last Sunday I ran with the rears 2psi higher and overall the car was pretty good. Since it was the first session of the year I left the VSA on and noticed it blink on a few times. The track I was on had a banked bowl/lightbulb turn that was pretty hard on the LF. I want to ease the load on that tire while reducing the tendancy for oversteer mid-corner so I can go faster at turn-in. Again it's not a problem right now, just a desire to find a little more speed, I was running with an E46 M3 who had about .3 (guessing) seconds per lap on me and I felt I could've been right there with him trading places and challenging each other if the tires were dialed in better.
Originally Posted By: gofast182
I'm primarily concerned with mid corner. This way I can carry more speed going in and I can deal with some oversteer on track-out. I do have a tweaked alignment and overall the car is quite neutral and easy to control.
Last Sunday I ran with the rears 2psi higher and overall the car was pretty good. Since it was the first session of the year I left the VSA on and noticed it blink on a few times. The track I was on had a banked bowl/lightbulb turn that was pretty hard on the LF. I want to ease the load on that tire while reducing the tendancy for oversteer mid-corner so I can go faster at turn-in. Again it's not a problem right now, just a desire to find a little more speed, I was running with an E46 M3 who had about .3 (guessing) seconds per lap on me and I felt I could've been right there with him trading places and challenging each other if the tires were dialed in better.
Sounds fun! Finding someone around the same speed is great to run with. A few tweaks and you could be right there.
I'm primarily concerned with mid corner. This way I can carry more speed going in and I can deal with some oversteer on track-out. I do have a tweaked alignment and overall the car is quite neutral and easy to control.
Last Sunday I ran with the rears 2psi higher and overall the car was pretty good. Since it was the first session of the year I left the VSA on and noticed it blink on a few times. The track I was on had a banked bowl/lightbulb turn that was pretty hard on the LF. I want to ease the load on that tire while reducing the tendancy for oversteer mid-corner so I can go faster at turn-in. Again it's not a problem right now, just a desire to find a little more speed, I was running with an E46 M3 who had about .3 (guessing) seconds per lap on me and I felt I could've been right there with him trading places and challenging each other if the tires were dialed in better.
Sounds fun! Finding someone around the same speed is great to run with. A few tweaks and you could be right there.
Originally Posted By: IndyIan
Sounds fun! Finding someone around the same speed is great to run with. A few tweaks and you could be right there.
I agree; back at a school in 2008 one instructor had a mildly tweaked 135i and a couple of others had hotted up Mini Coopers- we all had a ball running together(I was driving the MS3 that weekend).
Sounds fun! Finding someone around the same speed is great to run with. A few tweaks and you could be right there.
I agree; back at a school in 2008 one instructor had a mildly tweaked 135i and a couple of others had hotted up Mini Coopers- we all had a ball running together(I was driving the MS3 that weekend).
Originally Posted By: MCompact
Originally Posted By: IndyIan
Sounds fun! Finding someone around the same speed is great to run with. A few tweaks and you could be right there.
I agree; back at a school in 2008 one instructor had a mildly tweaked 135i and a couple of others had hotted up Mini Coopers- we all had a ball running together(I was driving the MS3 that weekend).
We had a duel of the dead slow dodges, Colt vs. atx Neon! To the death or headgasket failure... Its a pretty tight little track so there wasn't much waiting for the straights to be over atleast. I think I was running better lines but that colt would stick in the corners as it was probably 500lbs lighter with equal sized tires.
Originally Posted By: IndyIan
Sounds fun! Finding someone around the same speed is great to run with. A few tweaks and you could be right there.
I agree; back at a school in 2008 one instructor had a mildly tweaked 135i and a couple of others had hotted up Mini Coopers- we all had a ball running together(I was driving the MS3 that weekend).
We had a duel of the dead slow dodges, Colt vs. atx Neon! To the death or headgasket failure... Its a pretty tight little track so there wasn't much waiting for the straights to be over atleast. I think I was running better lines but that colt would stick in the corners as it was probably 500lbs lighter with equal sized tires.
I've always found that grip and speed isn't what makes track time fun. It's getting the car to the edge and holding it there.
My best race was on an old set of tires fighting to stay out of last place.
My best race was on an old set of tires fighting to stay out of last place.
Originally Posted By: gofast182
Assuming a car has 50/50 weight distribution will higher or lower rear tire pressure decrease oversteer? I always thought higher rear pressure did that but I talked to a racer this weekend who thought the opposite.
Front, rear, or all wheel drive has nothing to do with it. The basic physics involve changing "slip angle", which is drive independent.
To increase oversteer increase front tire pressure and/or reduce rear tire pressure.
To decrease oversteer decrease front tire pressure and/or increase rear tire pressure.
If you're doing this on a paved track with turns in one direction only, you may find that the left and right tires require different pressures. A tire pyrometer is always helpful.
Assuming a car has 50/50 weight distribution will higher or lower rear tire pressure decrease oversteer? I always thought higher rear pressure did that but I talked to a racer this weekend who thought the opposite.
Front, rear, or all wheel drive has nothing to do with it. The basic physics involve changing "slip angle", which is drive independent.
To increase oversteer increase front tire pressure and/or reduce rear tire pressure.
To decrease oversteer decrease front tire pressure and/or increase rear tire pressure.
If you're doing this on a paved track with turns in one direction only, you may find that the left and right tires require different pressures. A tire pyrometer is always helpful.
I don't recall saying anything about the drive wheels but I appreciate the reply. Even in this thread there are some opposing opinions.
Originally Posted By: gofast182
I don't recall saying anything about the drive wheels but I appreciate the reply. Even in this thread there are some opposing opinions.
It's not a matter of opinion, it's a matter of physics. I don't see a reference text on-line, but this is actually not a bad summary:
Oversteer
The key phrase is "slip angle".
I don't recall saying anything about the drive wheels but I appreciate the reply. Even in this thread there are some opposing opinions.
It's not a matter of opinion, it's a matter of physics. I don't see a reference text on-line, but this is actually not a bad summary:
Oversteer
The key phrase is "slip angle".
Originally Posted By: Wilhelm_D
It's not a matter of opinion, it's a matter of physics. I don't see a reference text on-line, but this is actually not a bad summary:
Oversteer
The key phrase is "slip angle".
And slip angle is a function of load, inflation pressure, and some tire parameters that can vary from tire to tire.
So, FWD/RWD/AWD does play a role, but it is much more complicated than that.
And we haven't even talked about spring rates and shock damping. Heck, even different tracks changes things.
It's not a matter of opinion, it's a matter of physics. I don't see a reference text on-line, but this is actually not a bad summary:
Oversteer
The key phrase is "slip angle".
And slip angle is a function of load, inflation pressure, and some tire parameters that can vary from tire to tire.
So, FWD/RWD/AWD does play a role, but it is much more complicated than that.
And we haven't even talked about spring rates and shock damping. Heck, even different tracks changes things.
CapriRacer points out my Camry's preferences...
The Camry is obviously a "touring" car, NOT a sports/performance ride..
My experience...
The Camry's door jamb spec is 29psi for the 15s that came on it...for comfort riding on OEM type tires....I had run 35 on them (51psi was max cold psi) and got even wear and better performance (for OEM tires)...and then...
When I upsized to 17" wheels and high performance tires that also had a max 51psi, I tried various PSIs and determined that 45psi was best....based on the "contact patch" showing dirt on the tread from shoulder to shoulder on the front, and a bit less on the shoulder on the rear...
I had run tests on those tires at 3psi increments over 30psi watching the tread contact patch for wear, but more importantly, testing results while running/braking/turning hard, testing on dry and wet pavement for lean, slipping, and directional stability, including "panic stops" (testing the ABS, as this is my first car with ABS), and relatively fast starts at stop lights/signs where oil drops collect to encourage slipping, to get a feel for how much I can "push" the Camry's daily driver characteristics, before settling on 45psi...
With a stick, there's a lot more to test as I'm responsible for controlling the engine's RPMs...
The Camry is obviously a "touring" car, NOT a sports/performance ride..
My experience...
The Camry's door jamb spec is 29psi for the 15s that came on it...for comfort riding on OEM type tires....I had run 35 on them (51psi was max cold psi) and got even wear and better performance (for OEM tires)...and then...
When I upsized to 17" wheels and high performance tires that also had a max 51psi, I tried various PSIs and determined that 45psi was best....based on the "contact patch" showing dirt on the tread from shoulder to shoulder on the front, and a bit less on the shoulder on the rear...
I had run tests on those tires at 3psi increments over 30psi watching the tread contact patch for wear, but more importantly, testing results while running/braking/turning hard, testing on dry and wet pavement for lean, slipping, and directional stability, including "panic stops" (testing the ABS, as this is my first car with ABS), and relatively fast starts at stop lights/signs where oil drops collect to encourage slipping, to get a feel for how much I can "push" the Camry's daily driver characteristics, before settling on 45psi...
With a stick, there's a lot more to test as I'm responsible for controlling the engine's RPMs...
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Originally Posted By: CapriRacer
So, FWD/RWD/AWD does play a role, but it is much more complicated than that.
It plays a role as to whether the vehicle in question tends to oversteer or understeer and to what degree.
However, in every situation relative to a specific vehicle increasing front tire pressure and/or reducing rear tire pressure will increase oversteer, while decreasing front tire pressure and/or increasing rear tire pressure will decrease oversteer.
So, FWD/RWD/AWD does play a role, but it is much more complicated than that.
It plays a role as to whether the vehicle in question tends to oversteer or understeer and to what degree.
However, in every situation relative to a specific vehicle increasing front tire pressure and/or reducing rear tire pressure will increase oversteer, while decreasing front tire pressure and/or increasing rear tire pressure will decrease oversteer.
Originally Posted By: Wilhelm_D
Originally Posted By: gofast182
I don't recall saying anything about the drive wheels but I appreciate the reply. Even in this thread there are some opposing opinions.
It's not a matter of opinion, it's a matter of physics. I don't see a reference text on-line, but this is actually not a bad summary:
Oversteer
The key phrase is "slip angle".
Well then I'll say there are opposing statements
. Anyway, that article was a very good read for anyone curious about what makes good handling. It got into the 'how' and 'why' just enough to be dangerous.
Originally Posted By: gofast182
I don't recall saying anything about the drive wheels but I appreciate the reply. Even in this thread there are some opposing opinions.
It's not a matter of opinion, it's a matter of physics. I don't see a reference text on-line, but this is actually not a bad summary:
Oversteer
The key phrase is "slip angle".
Well then I'll say there are opposing statements
When you start talking about "SET-UP" , tire pressure is a small piece of a very complex puzzle...
And even the pro's get it wrong sometimes, you often see a top team being slow at a couple of races, because they missed the set-up, and the car is EVIL handling.
And you have to compromise. Which corner (s) are most important? Are there slow corners where easy rotation will help... or are there fast corners where oversteer will KILL! you...
And, higher air pressure reduces contact patch ( past a certain psi, at least...) and increases tire spring rate, which "usually" increases oversteer on the rear.
Experiment, and take notes ... and don't get impatient and change 3 things at once...and ask (spy?) other competitors, especially those in the same car...
And even the pro's get it wrong sometimes, you often see a top team being slow at a couple of races, because they missed the set-up, and the car is EVIL handling.
And you have to compromise. Which corner (s) are most important? Are there slow corners where easy rotation will help... or are there fast corners where oversteer will KILL! you...
And, higher air pressure reduces contact patch ( past a certain psi, at least...) and increases tire spring rate, which "usually" increases oversteer on the rear.
Experiment, and take notes ... and don't get impatient and change 3 things at once...and ask (spy?) other competitors, especially those in the same car...
I'm going to say the opposite of what everybody else is saying based on personal experience and testing in my own cars, multiple platforms, on multiple tires, on multiple tracks, over multiple years.
Within a certain window, an increase in pressure will increase relative grip. If you go above that window grip goes away pretty dramatically. This is for stiff side-walled STREET tires, soft sidewall race compound tires tend to play by a different set of rules.
To tune tire pressures what you want to start out with is equal pressures at all four corners on HOT tires. Go for a few laps, duck into the pit lane, and quickly check your pressures; set all four corners to the same pressure.
Now simply tune as necessary. If you feel that the car is a bit more pushy than you'd like, maybe add 1 psi in each of the front tires and see what effect it has. If your pressures are already high, remove 1 psi from the rear. If you want the rear to stick harder, add 1 psi to the rear or take 1 away from the front. Keep adjusting 1 psi at a time until you're happy with the balance.
Within a certain window, an increase in pressure will increase relative grip. If you go above that window grip goes away pretty dramatically. This is for stiff side-walled STREET tires, soft sidewall race compound tires tend to play by a different set of rules.
To tune tire pressures what you want to start out with is equal pressures at all four corners on HOT tires. Go for a few laps, duck into the pit lane, and quickly check your pressures; set all four corners to the same pressure.
Now simply tune as necessary. If you feel that the car is a bit more pushy than you'd like, maybe add 1 psi in each of the front tires and see what effect it has. If your pressures are already high, remove 1 psi from the rear. If you want the rear to stick harder, add 1 psi to the rear or take 1 away from the front. Keep adjusting 1 psi at a time until you're happy with the balance.
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