PSA - Do NOT go by the PSI rating on your tire.
04-21-2012, 02:04 PM
#31
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There are quite a number of factors coming into play here. On a stock set of wheels the front cannot keep up with the rear and the car has built in understeer- a generally safer condition.
When you modify the car to improve cornering speed load factors change. with wider rubbber you need less pressure to support the deadweight load but then at higher cornering speeds you are putting more loads into the outer tire with weight transference. If you achieve equal weight front to rear then logic suggests a narrower front tire requries proportionately more air pressure.
On the autocross events I did there was little warm up time so I worked on the premis that the pressure I entered the course at was the effective [hot] pressure I was going to run at and with a full tank of gas I found that with a 265 front section and 295 rear the car seemed to work best with 36 psig front and 32 psig rear. If I was going to run hard on a ful track I would target something a bit less [10 to 15%] to allow for dynamic heating. This of course assumes no accurate tyre temperature monitoring capability.
Indeed the Michelin rep once even advised [when running on cup tires] to try running quite a bit lower [down to about 24 psig].
Out here with extremely warm summer temps, I have seen many tires wear out in the centre but never on the edges- I put this down to over pressurisation.
Fred
When you modify the car to improve cornering speed load factors change. with wider rubbber you need less pressure to support the deadweight load but then at higher cornering speeds you are putting more loads into the outer tire with weight transference. If you achieve equal weight front to rear then logic suggests a narrower front tire requries proportionately more air pressure.
On the autocross events I did there was little warm up time so I worked on the premis that the pressure I entered the course at was the effective [hot] pressure I was going to run at and with a full tank of gas I found that with a 265 front section and 295 rear the car seemed to work best with 36 psig front and 32 psig rear. If I was going to run hard on a ful track I would target something a bit less [10 to 15%] to allow for dynamic heating. This of course assumes no accurate tyre temperature monitoring capability.
Indeed the Michelin rep once even advised [when running on cup tires] to try running quite a bit lower [down to about 24 psig].
Out here with extremely warm summer temps, I have seen many tires wear out in the centre but never on the edges- I put this down to over pressurisation.
Fred
04-21-2012, 04:25 PM
#32
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Owners manual has line chart which show pressure change compared to temperature. For Nurburgring we usually lower pressure 0.5 bar under normal street to allow for extra heat. On autobahn normal 2.5bar on all corners has worked fine. Originally Porsche recommended slightly higher pressure than normal for really fast driving. With modern tires which work with less pressure anyway I don't think its needed unless speeds are faster than what can be used in traffic. Usually when high speeds are doable for longer periods its night time and weather is cooler.
475hp/460lb.ft
03-22-2017, 08:00 PM
#36
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Spring Bump - everyone check your tire pressure!!!
03-22-2017, 08:55 PM
#38
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03-21-2019, 11:25 PM
#40
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Spring Bump!!!
Check your pressures!!!!
It's very common for people to max out the tire pressure for storage (I do the same) to lessen chances of flat spotting. For this, the sidewall rating is the max you should go.
It's also very common for people to pull cars out of storage and forget to lower the PSI.......
Check your pressures!!!!
It's very common for people to max out the tire pressure for storage (I do the same) to lessen chances of flat spotting. For this, the sidewall rating is the max you should go.
It's also very common for people to pull cars out of storage and forget to lower the PSI.......
03-22-2019, 08:37 AM
#41
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That’s what I subscribe to on all of my cars. 44 psi is enough to loosen the fillings in my teeth. Regarding RDK, sensors in my ‘90GT are 3 bar in the rear and 2.5 front. System disabled because of bad sensors. At over $400 each (system takes a total of 8), I have better uses for my money. My early ‘93 system functions correctly and has 2.5 bar on all four wheels.
03-22-2019, 08:04 PM
#42
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With "modern tires", there's no need to run our cars at 44 psi. On any tires.
I run my tires (Michelin Pilot Super Sport, 18") at 32 psi (cold).
First, I get en even wear, and second, like the ride very much, way better than at 44...
I don't track my car. Can't say for those who does but to me, it's good.
RDK bypassed too.
I run my tires (Michelin Pilot Super Sport, 18") at 32 psi (cold).
First, I get en even wear, and second, like the ride very much, way better than at 44...
I don't track my car. Can't say for those who does but to me, it's good.
RDK bypassed too.
Last edited by Bertrand Daoust; 03-22-2019 at 09:04 PM.
03-22-2019, 08:15 PM
#43
Three Wheelin'
Rule of thumb for high performance "street" tires when used for driving on the track is to check the pressures when the tire is HOT. Pressure of 40 PSI hot is usually the best traction performance, and allows max rubber contact in cornering.
Tires like Hoosiers and Michelin Pilot Sport Cups use less pressure to get max performance.
Gary--
Tires like Hoosiers and Michelin Pilot Sport Cups use less pressure to get max performance.
Gary--
Usually, I try to keep the tires between 34-36 when street driving.
For a track day, Is it reasonable to start at 32 cold and expect 6-8 psi increase when hot?
Bear in mind this is Group 1 stuff so lives are likely not on the line!
I thought it was too convenient a stereotype... maybe not
No Vipers in my group...just me and 30 new Carrera S's ;(
