Rocha928

Does anybody know the correct tire pressure for a set of new tires (on new wheels) that I just mounted on my 1986 928 S?

Tires are Bridgestone Potenza S-03 Pole Position sizes 225/45YR17 front and 255/40YR17 mounted on 17-inch CupOne wheels. Wheels are 7.5-inches wide in front and 9-inches wide in rear.

My guess would be the stock tire pressure of the 1993 928 GTS; but I have not been able to find that information.

Thanks for any help you can provide.

Rocha928
1986 928S 5-speed
Kansas City

bad S4

I just received 17"X 9" and 10" SuperCup wheels mounted with Bridgestone SO2 Polepositions.
They came with standard 28 psi front and rear.
When I put them on the 928S4 understeer was
the condition.
I then set pressures to the S4 recommended
36 psi front and 44 psi rear.
The handling is again neutral but the ride
is firmer than I feel it needs to be.I will
lower pressures maintaining 8 psi difference
fr/rr until I reach a good compromise.
I hope this will be useful to you,but I am in the same boat.
O.Roberts
87 928S4
Blk/Blk
5-Speed
27k

Ed Ruiz

I believe the recommended tire pressures on a GTS is 36 psi all around. Personally, I use about 38 to 40 psi all around on the same wheels but with Pirelli All-Season tires.

So far, the grip is very good, the tires are wearing slowly and correctly, and the handling is neutral (partially because the car has stiffer springs, shocks, and swaybars).

Thom1

Rocha,

There is a factory sticker on my gas cap flap that specifies the following for my 1986.5: Tires: 225/50 VR 16, Pressure Front: 36, Rear: 44.

Ed Ruiz

That sticker is no longer applicable to the size wheels and tires being used. The pressures used on the GTS are more appropriate since the wheels are about the size of those used on a GTS. YMMV.

bad S4

To Ed Ruiz
Do you recommend 36 psi all around for
17" SuperCups and Pole Positions on an S4.
I am unsure to whom your responce was directed.
Is your car a GTS or S4.
How do you like the Pirellis.
Your reputation and experience are appreciated.
Thanks
O.Roberts
87 928S4
Blk/Blk
5-Speed
27k

Ed Ruiz

When it come to tire pressure recommendations, I can only tell you what Porsche recommends for a particular wheel size and what I have found works best for me.

My 928 is a GT with 7.5"x17" and 9"x17" C2 wheels. (Basically, the same size as the OEM wheels on a GTS.) Porsche recommends that the GTS tires should be inflated to 36 psi all around. I have found 36 psi to be a bit low for the roads I drive on and the way I drive. The handling is much improved when I inflate them to at least 38 psi. 40 psi works well for highway and winter driving.

The Pirellis are fine. I've had them now for almost two years, and they still have at least 75% of their tread. The grip is very good in all conditions, but winter driving is still not as sure-footed as I would like. Clearly, honest to goodness snow tires are best for driving in snow. All-Seasons, are a poor substitute for snow tires, but they do very well in all other conditions. YMMV.

For track and autocross, I have another set of wheels/tires with an "R" compound. They are extremely grippy, but are nearly useless in rain.

Thom1

Rocha,

Ed has a valid point. Your rear tires are now larger than the front. Therefore, they should handle more load with less pressure.

Does anyone have the FACTORY SPECIFICATIONS for tire sizes and corresponding pressures for sizes that differ from front to rear. This would appear in the owner's manual or on the gas flap. Perhaps some cars come with factory specific variable tire sizes.

My specifications earlier are factory specific for my car. They are re-iterated in the owner's manual. The factory does not call for variable tire sizes between front and rear for my car. BTW, the S3 1986.5 comes with the 1987 S4 suspension.

Rocha928

Thanks for all the input!

Going to try 36 psi front and 38 psi rear and see how that works out.

Rocha928
1986 928S w/ 17-inch cup wheels
Kansas City