PSI build up in "new" tires, what is the expected norm?

Just a curious observation that I want to share and validate.

Before NSXPO 2003, I installed a set of new Yoko AOH22 oem tires on my 16/17. Drove about 500 miles before getting onto the track at Infineon.

The pressure build up in the first session was about 8 psi in the rear and they were reading 36 front and 45 rear! I had started with 31 and 36 cold and I was taking it easy as I had a lot of wiggle in the rear given they were not heat cycled yet.

Got them down by 3 psi and the following session driving a little more aggressively, they got back up to 36 and 44! So that is almost 12 psi from cold on the rears. Lowered them again and by the end of the day I was getting closer to my normal running temps but they were over my benchamrak of 31 and 40 when hot. On my older Yokos, the pressure build up was no more than about 5-6 psi on the fronts and 7-8 psi in the rears.

Well this weekend I was at Infineon again, and started again with 31 and 36 as we had wet track and it was drizziling. I normally start with an aim to get at 27-28 front and 33-34 rear cold. The morning sessions were easy driving. By afternoon as the track dried and the sun started to come up, the pressure started to get back by about 10 psi on the rear and 7 on the front. Lowered it down by 2 psi ...... following sessions they got back to 36 and 44 ........ car was still wiggly at some sections and I could tell it was from too much tire pressure so had to take cool down laps before picking the pace again ......

So my question is this, how many heat cycles does a "new" high performance street tire need to go through to settle down, or how many street miles does it take? I have now some 1100 miles on these tires, of which 330 miles are on the track - 200 miles qualify as really pushing the tires.

Newer tires have deeper tread blocks, which means you get more "tread squirm" when driving them hard, which means more heat. As the new tread wears down they'll build less heat with the same use. No magic numbers, just less tread = less heat. This why people shave tires for track use.

Just to give you an idea which pressure a "no tread" tire can build up (please do the bar/PSI math): I start a track session with Yoko A 005 race slicks (210-580/16 front, 250-610/17 rear) cold 1.5 bar front and 1.7 rear. After 15 hot track minutes it usualy gets up to 2.1 front and 2.3 rear - the ideal pressure for this tire and the NSX. Sometimes it's even about 0.2 more but then I reduce the hot pressure.

In any case, no matter what kind of tire: Always re-check the pressure after the first 10-15 track minutes.

NSX-Racer said:

please do the bar/PSI math

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Sure, no problem.

1 bar = 14.5037737730209 pounds per square inch of pressure. Recalculating the previous paragraph into psi yields the following results:

I start a track session with Yoko A 005 race slicks (210-580/16 front, 250-610/17 rear) cold 22 psi front and 25 psi rear. After 15 hot track minutes it usualy gets up to 30 front and 33 rear - the ideal pressure for this tire and the NSX. Sometimes it's even about 3 psi more but then I reduce the hot pressure.

Make sure you use air-line dryer to ensure dry air in your tire to minimize pressure build up on higher temperature. The moisture in the air inside your tire can cause the pressure increase dramatically. I'm not surprise seeing 10-12 psi increase.

IF you run Nitrogen, or air that has been dried up using a dryer, usually the increase is aroun 5-7psi.

Andrie Hartanto said:

Make sure you use air-line dryer to ensure dry air in your tire to minimize pressure build up on higher temperature. The moisture in the air inside your tire can cause the pressure increase dramatically. I'm not surprise seeing 10-12 psi increase.

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Since any moisture is already vaporized, why would the rise in temperature cause the the water vapor to increase in pressure at a greater rate than the air? Physics says PV=nRT, so a given increase in temperature should make the pressure increase at the same rate, regardless of which gas is involved.

nsxtasy said:

Since any moisture is already vaporized, why would the rise in temperature cause the the water vapor to increase in pressure at a greater rate than the air? Physics says PV=nRT, so a given increase in temperature should make the pressure increase at the same rate, regardless of which gas is involved.

Click to expand...

It is not completely vaporized. The moisture content in the air is what contributed on the big jump on the pressure build up.

Hrant,I noticed the same thing! I was using relativley new unshaved RA-1's and I started at my usual 32 psi all around,and because of the hectic first day with the school and all, I only got to check my hot pressures once and wholy cow 42 front and 45 rear!I could feel the car as loose!Day two saw me watching more closely and once I got em down to 38-39 hot it was all good.obviously what is usual setup for me in the NE is not proper for the conditions we had at Infineon.I agree with the others about what makes tires hotter,also my feeling is that I did'nt take into account the hotter track temps than I'm used to as well as the track layout-no real striaghts,the tires are always turning or transfering wght,plus we always had "reward wght" passengers and I usualy had 80-100 kg riders,these things make a diference!