Tire Pressure

[Gawernator]

Looking at my owner's manual today, I'm a little puzzled. The 944 NA side says use pressure 29/36 PSI. But the turbo page says 36/36 all around. I have the optional turbo size tires and 951 Fuchs, so should I just go up to 36 PSI all around? It's confusing because my size 205/55 and 225/50 is listed for both 944 and 951 but different pressures.

[bordin34]

Open the fuel door. The proper pressure should be there.

[Gawernator]

The fuel door says 29/36 just as the manual does. I'm just puzzled why the 951 has different tire pressure when I have the same exact wheels and tire size?

[Dantilla]

Different pressure for different size tires.

NAs use the same tires on all four corners, while Turbos use staggered sizes.

Factory settings will induce minor understeer.
Go ahead and adjust pressure to suit your own driving preferences.

[flash968]

yup - they dropped the tire pressure up front to induce a touch of understeer.

this isn't cast in stone, but as a general rule:

start at 36 cold all around. draw a chalk line across the tread of the tire. go drive for a bit. see how it wears. if you aren't wearing the corners, drop the pressure a bit. if you are wearing the corners of the tires more than the middle, raise it.

then check the hot pressures. you are looking for about a 3 lb increase in the winter, and a 4-5lb increase in the summer. if you have more increase than that, your starting pressure is too low. if you have less increase, then count yourself lucky.

the idea is to find a pressure that provides the most even tire wear, and the lowest increase in temps from cold to hot. this will give you the best adhesion and tire life.

[ernie9944]

Fuchs with 205/55 225/50 in your part of the wood (California) best combo is 29psi front 34psi rear.

[Gawernator]

That's a neat trick. Why 29/34? It's about 37° F out today, actually. I'm also wondering how gas mileage is affected by this, on a DD naturally mileage and long tire life are important.

[flash968]

tires today are very different than tires of 1985. the specs printed on the car are pretty much useless.

you really can't say "here's your pressure" anyway. the best you can do is have a starting point.

the sidewall construction of a particular tire can alter the results by as much as 4lbs all by itself. generally, a soft sidewall tire needs more air than a stiff sidewall tire.

that's why you have to use the chalk, or better yet, a tire temp gauge, and see how your tires respond on your car.

[Volhv]

An alternative to chalk is white shoe polish.... the liquid stuff that has the foam top.

My gas filler door has the tire size, and pressure for the 15" but the car had 16" phonedials when I got it. I'll be putting on some 15" Fuchs once I get it back on the road.

[Gawernator]

I have enough Kiwi Black shoe polish to last through the cold war, but none white! I do have chalk though.

[CHICKS]

I've played around with tire pressure and ended up just going with what the gas door says, 29/36. To me the car feels best at that pressure, and they are wearing just fine.

[Gawernator]

What size tires and wheels do you have CHICKS?

[flash968]

as an example of tire pressure being subject to change based on brand, on the blue car, i had S0-3s on there. i had to run the rear at 34 and the front at 35 in the summer and 36r and 38f in the winter. then i went to the AD-08 and due to the construction difference in the tire, i had to bump up both ends by 2 lbs in the summer and 4lbs in the winter. same size tire in both cases.

[9FF]

I was told by a Porsche dealer the difference in na/turbo tire pressures was because the turbo was heavier at the front. Definitely nothing to do with staggered tires, my 86na came from the factory with staggered Fuchs and the pressures on the gas filler door still say 29/36.

[Gawernator]

I thought about that too. The turbo has the turbo, intercooler, plumbing etc. But does it really weigh that much more? 7 psi seems like a lot

[Dantilla]

Originally Posted by 9FF

... my 86na came from the factory with staggered Fuchs and the pressures on the gas filler door still say 29/36.

But the tires were originally 215/60/15 on both the 7" fronts and the 8" rears, correct?

Original sizes were 215 on all four for NA cars, 205/225 on the Turbos.

Moot point for many of us. My car currently has 17" Fikse wheels with tire sizes the factory never though of in 1987.

The turbo weighed slightly more than NA cars, but still had about perfect 50/50 distribution.

[Gawernator]

16" Fuchs, don't think it makes a difference

[CHICKS]

Originally Posted by Gawernator

What size tires and wheels do you have CHICKS?

215 60/15, Falken Ziex ze-512's on early offset 15x7 phone dials.

[9FF]

Quote de 9FF

... my 86na came from the factory with staggered Fuchs and the pressures on the gas filler door still say 29/36.

But the tires were originally 215/60/15 on both the 7" fronts and the 8" rears, correct?



Original sizes were 215 on all four for NA cars, 205/225 on the Turbos.



Moot point for many of us. My car currently has 17" Fikse wheels with tire sizes the factory never though of in 1987.



The turbo weighed slightly more than NA cars, but still had about perfect 50/50 distribution.

Tires were the same f&r but the rear track was wider by about an inch. The early offset cars with staggered 15in Fuchs had the widest stock track at the rear, wider than all the other na or turbo models.

Also, as I said the turbo is heavier by over 100LB and mostly at the front. That is considerable and I still beleive what I was told by the dealer, that its the reason turbos have a higher front tire psi.

[JAXTURBO]

Just my 2 cents, and I am by no means a tire expert, but I know what feels comfortable/safe to me. I'm running 16" phonies with 225 up front and 245 in rear on a 951. 30/36 psi is what I run. I like the way it feels going into a "sporty" corner. Myunderstanding is that under heavy cornering loads, the fronts want to roll onto the sidewalls. So if you stiffen up the sidewalls a bit (with increased air pressure) they tend to stay planted.