Tire Pressure for track days
05-13-2019, 02:03 PM
#1
Rennlist Member
Thread Starter
Tire Pressure for track days
What do you all recommend my hot tire pressures be when at the track?
1988 944 Turbo
Kumho ECSTA PS91
245/35 ZR18
265/35 ZR18
Thanks!!
1988 944 Turbo
Kumho ECSTA PS91
245/35 ZR18
265/35 ZR18
Thanks!!
05-13-2019, 04:49 PM
#2
Rennlist Member
Check your tyre pressure as soon as you can after the cool down lap. I aim for hot tyre pressues of 34 - 35 psi with ultra hi perf road spec tyres. Keep checking after each run because as you gain confidence they will increase during the course of the day.
05-13-2019, 07:39 PM
#4
Rennlist Member
I tend to start at 28-29 cold and then you will find that the temp will rise after your first run. When you come in with tyres hot after the first run then adjust up or down to 34-35 and then check and adjust regularly during the day.
05-14-2019, 10:47 AM
#6
Three Wheelin'
I think you are on the right track. As a rule of thumb, I tell my students to aim for the manufacturer's recommended cold pressure as their goal for hot pressure coming off the track, and adjust up or down from there depending on how the car feels, ambient temperature, etc.
Tire manufacturers warn against going out on track with too low of a tire pressure (can damage the tire), so once you figure out your optimal hot pressures, don't let all of the air out at once before your first session of the morning---let 3-4 PSI out and then let more out after the first session until you settle in on your target.
Tire manufacturers warn against going out on track with too low of a tire pressure (can damage the tire), so once you figure out your optimal hot pressures, don't let all of the air out at once before your first session of the morning---let 3-4 PSI out and then let more out after the first session until you settle in on your target.
05-14-2019, 05:27 PM
#7
Pro
The more complicated answer is, 'it depends'. If you're not aiming to do anything too scientific or perfectly optimize your traction for each track you run on, just follow the advice above.
There is likely some room for improvement if you're willing to do more. It will involve repeated runs with repeated camber and pressure adjustments. There is an 'ideal' pressure and camber combination at which you will see a 10 degree F drop between the inside and outside of the tire, and the middle of the tire should be right in between those two temps (you'll have to be able to adjust camber to dial in the center temp exactly between the inner and outer temp). Too much camber or pressure, the inside will be much hotter, too little camber or pressure, the outside will be hotter.
For a really simple approach on regular road-going tires (not R-spec track tires), let's say you get a 'track alignment' for your car that has a slightly more aggressive camber setting (and a little bit of toe-out on the front to run better through the corners), and you're not going to change the camber at the track. You'll go through the following iterative process:
1) Check the inside, middle, and outside temp of each tire as soon as you complete your run.
2) If the inside temperatures are not 10 degrees hotter than the outside, increase the pressure on that tire. If the inside temp is more than 10 degrees hotter, lower the pressure.
3) Repeat on the next run.
Write all of these down after each run. It will tell you a lot about how your car is handling, and what kinds of suspension changes you may want to make in the future.
Here's a good worksheet to track your tire temperatures for each run:
http://www.longacreracing.com/Userfi...Temps-Form.pdf
There is likely some room for improvement if you're willing to do more. It will involve repeated runs with repeated camber and pressure adjustments. There is an 'ideal' pressure and camber combination at which you will see a 10 degree F drop between the inside and outside of the tire, and the middle of the tire should be right in between those two temps (you'll have to be able to adjust camber to dial in the center temp exactly between the inner and outer temp). Too much camber or pressure, the inside will be much hotter, too little camber or pressure, the outside will be hotter.
For a really simple approach on regular road-going tires (not R-spec track tires), let's say you get a 'track alignment' for your car that has a slightly more aggressive camber setting (and a little bit of toe-out on the front to run better through the corners), and you're not going to change the camber at the track. You'll go through the following iterative process:
1) Check the inside, middle, and outside temp of each tire as soon as you complete your run.
2) If the inside temperatures are not 10 degrees hotter than the outside, increase the pressure on that tire. If the inside temp is more than 10 degrees hotter, lower the pressure.
3) Repeat on the next run.
Write all of these down after each run. It will tell you a lot about how your car is handling, and what kinds of suspension changes you may want to make in the future.
Here's a good worksheet to track your tire temperatures for each run:
http://www.longacreracing.com/Userfi...Temps-Form.pdf
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05-14-2019, 08:22 PM
#8
Rennlist Member
The more complicated answer is, 'it depends'. If you're not aiming to do anything too scientific or perfectly optimize your traction for each track you run on, just follow the advice above.
There is likely some room for improvement if you're willing to do more. It will involve repeated runs with repeated camber and pressure adjustments. There is an 'ideal' pressure and camber combination at which you will see a 10 degree F drop between the inside and outside of the tire, and the middle of the tire should be right in between those two temps (you'll have to be able to adjust camber to dial in the center temp exactly between the inner and outer temp). Too much camber or pressure, the inside will be much hotter, too little camber or pressure, the outside will be hotter.
For a really simple approach on regular road-going tires (not R-spec track tires), let's say you get a 'track alignment' for your car that has a slightly more aggressive camber setting (and a little bit of toe-out on the front to run better through the corners), and you're not going to change the camber at the track. You'll go through the following iterative process:
1) Check the inside, middle, and outside temp of each tire as soon as you complete your run.
2) If the inside temperatures are not 10 degrees hotter than the outside, increase the pressure on that tire. If the inside temp is more than 10 degrees hotter, lower the pressure.
3) Repeat on the next run.
Write all of these down after each run. It will tell you a lot about how your car is handling, and what kinds of suspension changes you may want to make in the future.
Here's a good worksheet to track your tire temperatures for each run:
http://www.longacreracing.com/Userfi...Temps-Form.pdf
There is likely some room for improvement if you're willing to do more. It will involve repeated runs with repeated camber and pressure adjustments. There is an 'ideal' pressure and camber combination at which you will see a 10 degree F drop between the inside and outside of the tire, and the middle of the tire should be right in between those two temps (you'll have to be able to adjust camber to dial in the center temp exactly between the inner and outer temp). Too much camber or pressure, the inside will be much hotter, too little camber or pressure, the outside will be hotter.
For a really simple approach on regular road-going tires (not R-spec track tires), let's say you get a 'track alignment' for your car that has a slightly more aggressive camber setting (and a little bit of toe-out on the front to run better through the corners), and you're not going to change the camber at the track. You'll go through the following iterative process:
1) Check the inside, middle, and outside temp of each tire as soon as you complete your run.
2) If the inside temperatures are not 10 degrees hotter than the outside, increase the pressure on that tire. If the inside temp is more than 10 degrees hotter, lower the pressure.
3) Repeat on the next run.
Write all of these down after each run. It will tell you a lot about how your car is handling, and what kinds of suspension changes you may want to make in the future.
Here's a good worksheet to track your tire temperatures for each run:
http://www.longacreracing.com/Userfi...Temps-Form.pdf
05-15-2019, 02:01 AM
#9
Three Wheelin'
The more complicated answer is, 'it depends'. If you're not aiming to do anything too scientific or perfectly optimize your traction for each track you run on, just follow the advice above.
There is likely some room for improvement if you're willing to do more. It will involve repeated runs with repeated camber and pressure adjustments. There is an 'ideal' pressure and camber combination at which you will see a 10 degree F drop between the inside and outside of the tire, and the middle of the tire should be right in between those two temps (you'll have to be able to adjust camber to dial in the center temp exactly between the inner and outer temp). Too much camber or pressure, the inside will be much hotter, too little camber or pressure, the outside will be hotter.
For a really simple approach on regular road-going tires (not R-spec track tires), let's say you get a 'track alignment' for your car that has a slightly more aggressive camber setting (and a little bit of toe-out on the front to run better through the corners), and you're not going to change the camber at the track. You'll go through the following iterative process:
1) Check the inside, middle, and outside temp of each tire as soon as you complete your run.
2) If the inside temperatures are not 10 degrees hotter than the outside, increase the pressure on that tire. If the inside temp is more than 10 degrees hotter, lower the pressure.
3) Repeat on the next run.
Write all of these down after each run. It will tell you a lot about how your car is handling, and what kinds of suspension changes you may want to make in the future.
Here's a good worksheet to track your tire temperatures for each run:
http://www.longacreracing.com/Userfi...Temps-Form.pdf
There is likely some room for improvement if you're willing to do more. It will involve repeated runs with repeated camber and pressure adjustments. There is an 'ideal' pressure and camber combination at which you will see a 10 degree F drop between the inside and outside of the tire, and the middle of the tire should be right in between those two temps (you'll have to be able to adjust camber to dial in the center temp exactly between the inner and outer temp). Too much camber or pressure, the inside will be much hotter, too little camber or pressure, the outside will be hotter.
For a really simple approach on regular road-going tires (not R-spec track tires), let's say you get a 'track alignment' for your car that has a slightly more aggressive camber setting (and a little bit of toe-out on the front to run better through the corners), and you're not going to change the camber at the track. You'll go through the following iterative process:
1) Check the inside, middle, and outside temp of each tire as soon as you complete your run.
2) If the inside temperatures are not 10 degrees hotter than the outside, increase the pressure on that tire. If the inside temp is more than 10 degrees hotter, lower the pressure.
3) Repeat on the next run.
Write all of these down after each run. It will tell you a lot about how your car is handling, and what kinds of suspension changes you may want to make in the future.
Here's a good worksheet to track your tire temperatures for each run:
http://www.longacreracing.com/Userfi...Temps-Form.pdf
The original poster sounds like a relative newcomer to track events, so I would instead suggest the old autocross trick of marking the edge of the tire tread/sidewall interface with chalk (marked by a triangle on many tires, or a small Michelin man on tires made by that brand), and monitoring how close the treadwear runs to to mark. If the tread is not wearing all the way to the mark, decrease the tire pressure in small increments (say 2 PSI) until it does. If it runs over the edge, pressures are too low, so add accordingly. This seems like a very low-tech method, but it has proved very effective for me and for various students for over a dozen years.
Once you are more advanced with your setup and can get other people to come to the track with you, tire temperature monitoring is indeed a more effective method, but only if the temperatures are measured properly with the tire at full temperature. These days, it is even be feasible for the committed track day junkie to have an onboard infrared tire temperature monitoring system at each corner, which interfaces with an existing telemetry system.
05-15-2019, 11:59 PM
#10
Racer
Join Date: May 2008
Location: Encinitas, ca PCA National DE instructor PCA San Diego chief driving instructor
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Your desired hot pressures are also dependent on how you want the tires to feel. I am assuming proper chassis setup for the running pressures.
More pressure gives more grip (up to a point), but along with increased grip comes reduced feedback. This is great if you're the local hotshoe, not so much if you are more of a beginner to track driving where a lot more feedback is better than a little more grip.
It is also useful to note that different tires react differently to temperature. Street tires tolerate less heat before turning greasy than spec R tires or slicks. Real track tires don't have much grip until ~140 degrees, and give up at 200-240 (depending on the tire), street tires work on the first lap.
Just for reference, I shoot for 36/36 hot on RE71Rs, 40/39 on Hoosier R7s. My car weighs 2998 with me in it and a full tank, and makes 330 at the wheels. 275/40-17 on 9" square, 750/900 pound spring rates. These inflation pressures reveal the fact that the tires are too small for the car's power and weight, but rules are rules.
More pressure gives more grip (up to a point), but along with increased grip comes reduced feedback. This is great if you're the local hotshoe, not so much if you are more of a beginner to track driving where a lot more feedback is better than a little more grip.
It is also useful to note that different tires react differently to temperature. Street tires tolerate less heat before turning greasy than spec R tires or slicks. Real track tires don't have much grip until ~140 degrees, and give up at 200-240 (depending on the tire), street tires work on the first lap.
Just for reference, I shoot for 36/36 hot on RE71Rs, 40/39 on Hoosier R7s. My car weighs 2998 with me in it and a full tank, and makes 330 at the wheels. 275/40-17 on 9" square, 750/900 pound spring rates. These inflation pressures reveal the fact that the tires are too small for the car's power and weight, but rules are rules.
05-16-2019, 01:24 AM
#11
Race Car
The pressure increase from cold to hot is dependent on the weight of the car.
On a 2600lb Spec 2 944, cold @ 26 psi yields 34 psi hot (Hankook C71 and Hoosier R7), depending on track surface temperature.
Over 34 psi, sliding greasy feeling feedback.
If you have a friend, yes, get temps/pressures straight off the track as soon as rolled to a stop.
Avoid running last lap to session end if you want legit feedback as a cool down lap to pits at slower pace negates data.
Tire temps/pressures will rise from the transfer of heat from the brakes increasing readings if car sits even 1 minute hot.
In enduros, the mandatory 5 minute stop, I jump the wall and bleed down to 32 psi to give 2 psi headroom for final leg of enduro.
I have finished all my service, cleaning windshield, looking under car, handing a drink bottle, maybe even check wheel torque in 2-3 minutes and for kicks I'll sometime check 1-2 tires again and will have come up 2 psi from the heat of brakes/wheels in that 3 minute period without cooling air flow on the brakes.
If you are using an alignment more oriented to track than street, get yourself a tire pyrometer and monitor temps across tire width using tread location to remain consitent.
Record 3 readings, inside, center, outside of tire.
You'll know what to do from there.
T
On a 2600lb Spec 2 944, cold @ 26 psi yields 34 psi hot (Hankook C71 and Hoosier R7), depending on track surface temperature.
Over 34 psi, sliding greasy feeling feedback.
If you have a friend, yes, get temps/pressures straight off the track as soon as rolled to a stop.
Avoid running last lap to session end if you want legit feedback as a cool down lap to pits at slower pace negates data.
Tire temps/pressures will rise from the transfer of heat from the brakes increasing readings if car sits even 1 minute hot.
In enduros, the mandatory 5 minute stop, I jump the wall and bleed down to 32 psi to give 2 psi headroom for final leg of enduro.
I have finished all my service, cleaning windshield, looking under car, handing a drink bottle, maybe even check wheel torque in 2-3 minutes and for kicks I'll sometime check 1-2 tires again and will have come up 2 psi from the heat of brakes/wheels in that 3 minute period without cooling air flow on the brakes.
If you are using an alignment more oriented to track than street, get yourself a tire pyrometer and monitor temps across tire width using tread location to remain consitent.
Record 3 readings, inside, center, outside of tire.
You'll know what to do from there.
T