jlbjr

BLK06ZO6

Bill Dearborn

This sort of depends on how the car is being driven. The recommended cold pressure for street driving is 30 psi. I don't bother looking at what the warm temp pressures are since almost all street driving results in warm tire temps at best. On track GM recommends a 26 psi cold pressure setting which usually turns up right around 32 psi hot. A hot tire is when the tread is running at 190 degrees F it takes about 5 miles of triple digit speeds and hard cornering to get up to that temp. I have never seen a street/highway tire temp go over 150 deg F even when pushed as hard as you can get away with.

Bill

X25

In Europe, sustained high speed driving can also overheat the tire, even when the car is driven just straight, due to much higher speeds allowed on some of the highways in some of the countries. Other than that, it's indeed pretty hard to overheat, or even properly warm up tires at the street.

Back to the question, especially in colder weather, lower pressure helps. It lets the tire flex more, causing more heat build-up, which is what you need at low temps. I've recently dropped mine to 26 PSI for street (PSS ZP). This helped me gain 3 PSI during my commute (i.e. higher temp increase) compared to ~ 2 PSI I did when I started from 30 PSI in similar conditions. Due to this, the tires will wear out quicker, or possibly uneven, and fuel mileage will suffer, too, but as is I'll take any more grip I can get from these tires, that seem to be awful for any cold weather.

BLK06ZO6

X25

My 2 cents (brainstorming)
Your tires need to get to that 180-200 F range, especially those that require warm-up for best performance. There's roughly about 0.7 PSI increment for every 10 degees F gain. 180-70 (ambient) is delta in temp, ~110. 11x0.7=7.7 PSI gain is expected. No wonder I commonly see 7-8 PSI increase during a session.

Anyway, if you want 32 hot, it means 24 or so cold in these conditions. You could start with 24 instead, but you should make sure to not push it too much or do too much speed before it warms up to 26+ PSI. 1-3 PSI of pressure creep is also very common during the day, as ambient temps pick up (usually by 3 PM).

This is all good if tires do warm up. What if they don't? Heat cycled tires warm up slower, for instance. What if ambient temps drop, but you can't reach your target hot pressures? Do you increase your cold pressures to hit your targets? That's probably the wrong course of action, since higher cold pressures will allow even less flex, and you'll get to even lower tread temps than you were getting (much less than 180), even though target pressure is achieved. So now, you need to choose: lower cold pressures that help warm up the tire, but might not hit 32 PSI, which might not give you the optimal tread shape? Or higher cold temps to hit your targets and tread shape? I usually prefer the former, but there's no one clear answer, since it depends on the flexibility of compound. With PSS ZP or Cup2 ZP, I'd lower initial cold pressures since those tires are useless without high temps, and ZP profiles can support lower pressures safer than most other tires. With R888R, I'd focus more on hitting my pressure goals since this compound tends to overheat anyway.