SC tire pressure

[PorscheAmateur]

So I have a 1980 911sc. Just yesterday, i took the car out and the tires didn't feel like they were very inflated. The tires are michelin all season performance something that say max of 51 psi. Not sure what Porsche recommends for tire pressure. So my question is, what should I have the tires inflated at?

[NoYouRelax]

My tires say max 51 psi too. The ride gets real sloppy when the tire pressure is low (in 30s), so I try to keep them around 45 psi. I am interested to find out what others say too.

[PorscheAmateur]

By the way, I had them inflated at 45 all around yesterday

[Oh Haha]

Way too much air in the tires!

29 front, 34 rear is the factory recommendations for SCs.

You should have a sticker in the engine compartment staing the pressures.

Remember to check the pressures when cold.

[kach22i]

Originally Posted by Oh Haha

Way too much air in the tires!

29 front, 34 rear is the factory recommendations for SCs.

You should have a sticker in the engine compartment staing the pressures.

Remember to check the pressures when cold.

The information is also in the owner's manual.

I used a Sharpie to write on the inside of the door jamb where it is found on American cars.

If I recall correctly, the rear tire pressure goes up over the years as the motors get larger and heavier.

[RedCoupe]

The front/rear tire pressure differential is important to minimize oversteer. So, if you decide to try a different pressure on one end, be sure to change the other end by a similar amount.

[PorscheAmateur]

Just set fronts to 29 and rear to 34. Feels better and drives better. Thanks everyone

[jadatis]

Tire pressure is a bit more complicated then that.
I once got hold of the formula the European tire-makers use to determine pressure for a load, and went running with it. Gathered a lot of information in time.
Even found out some foults in the system.

For calculating the lowest pressure at wich the tires dont get damaged by the 10 to 30 times a second deflecting and flexing back of every segment of the tire , I need the next.

From tire :
maximum load or loadindex

Pressure needed for that called the reference-pressure ( Pr) and is not the maximum pressure of yours 51 psi. If you see XL/reinforced/ Extraload on the tire, then its such a tire and needs 41psi /2.8bar for the maximum load to ride up to mostly 160km/99m/h with camber angle of below 2 degrees.
Normal car tires , called P-tires in America need 35psi Pr.
For higher speed the Pr has to be highenend up with a system depending on the speedcode of tire ( V to Y ,(Y) for Porche).

Also need the sises and that speedcode.

From Car :
Empty weight and the way you load it ( persons and load) .
Motor in front or back.
This is to estimate the axle loads in your normal use.
For fully loaded the GAWR and GVWR ( gross axle/vehicle weight rating).
Camber angle of mostly rear wheels done ( wheels like this on the axle/-\)
Maximum technical car speed or speed you sertainly wont go over in your use.

Try to find all that or most of it and give it here, and I will calculate that lowest pressure , wich you can play with above that for handling and over and under steer.

[nineball]

for those of you not mathematically inclined there is a much simpler way. draw a chalk line across the tread of your tires and roll the car back and forth. if the chalk wears off more in the middle you have too much air pressure. if it's the ends that are worn you have too little air. when you can get the chalk line to wear off evenly your pressure is right.

[jadatis]

But be carefull with the chalk test.
Begin at much to high pressure and work your way down until line wears of evenly , then stop.
If you go on until the sides wear of more then middle , and take the last step where it wears evenly , there is even pressure on the tire treath, but the sidewall can still bend to much wich gives that kind of damage that a blowing tire can occur.

Radial car tires have a large range at wich the widht of the treath stays evenly on the ground, and the sidewall-bending is more important for tire live and savety.

[Flojo]

32 psi (2,2 bar)