Which Tyre Pressures?

[pete917]

Its the age ld question I kow, but what tyre pressures would you recommend my wheel and tyre set up

Front: 205 x 55 x 16
Rear: 245 x 45 x 16

Would it be the same for road and track use?

Many thanks Guys

[Oh Haha]

The factory pressures are fine. You can find them listed on the engine panel when you lift the lid.


I run my same size tires at 30 f, 34 r.

Track use will be the same unless you are trying too dial the car in at a specific track in which case you will just need to test different pressures. Even more intense would be to utilize a pyrometer to check tire temps.

[tcar]

You could go a few pounds higher/lower, just keep a 4-5 pound difference f-r.

[RWebb]

32/34

Todd Serota told me about that years ago & it works great on 911s or the Boxster I used to have

stock pressures (F-R differential) is to get more understeer and reduce novice crashes that P AG had to deal with

[pete917]

Thanks guys.

I found out yesterday that porsche recommend 29/34 psi front/rear for my tyre sizes. I played with the pressures yesterday and I ended up with 30/34 psi.

What differene getting the pressures right makes....

I spoke to a friend of mine who races his 911 and he runs 30 psi all round.

I assume that the pressures effect grip and therefore the difference in pressures(grip) can help with under/over stear?

[Flieger]

Yes, pressures affect over/understeer but there are way too many variables to give accurate predictions.

#1 Tire makeup: compound, tread pattern.
-Rubber chemical composition makes all the difference. The rubber is designed to work in a specific temperature range based on its intended use. Race tires usually like hot temps. Rain tires like cooler weather. This means winter tire rubber is softer and grippier but when used in hot temps, it gets greasy, squirmy, and breaks down. Lower pressures can put more heat into a tire if it needs it.

-Tread pattern will affect how much the tread blocks squirm under side and braking/accelerating forces. Tire pressure affects the sidewall stiffness and how much the tread rolls under in a turn.

#2 Vehicle weight.
-Heavier cars need higher pressures in general. More weight in the rear needs a greater pressure differential.

#3 Tire size.
-Wider tires may need lower pressure to get heat into them. Taller tires need higher pressures to prevent roll-under.

#4 Driver handling preference.
-After all the above are held constant, you can change pressure differentials to change the over/understeer balance. Higher tire pressures result in a sharper, lighter steering feel and less roll-under so the front responds quicker. If you go higher than optimal, though, you will gain that quick response at the expense of understeer in sweepers. This is just like tuning springs.

etc., etc., etc.