regular street tire pressure?

[Cdnone1]

I know that tire pressure is a Dark Science and ask ten people and you will get ten different answers, but....
What is the best tire pressure for regular street driving. I recently had the alignment and corner balanced done on my car. I was shocked at the end of it that they checked my tire pressure and put 40 lbs in the front and 42 lbs in the rears! I thought the factory recommended 29/32
So here are the states on my car and I am looking for suggestions to get the maximum performance out of my tires( I don't really care about the life of them or I wouldn't be running neg camber)
Thanks

1982 SC
2387 lbs
Carrara sway bars
21/26 torsion bars
running 225/50 on 7" front 245/45 on 8" rear
Dunlop Sport 8000
.75 degree negative camber front/1.60 negative rear
Lowered to Euro specs
Also I live in So Cal so the weather is a constant (70-80's) and I don't take the car out in the rain because driving in the rain in LA is like playing a giant game of dodge ball with your car.

Anyone else run a similar set up? I just got a compressor so playing around with tire temp is no problem but would like to hear from other members experience, also please what temps do you run on the street verses track
Here's a picture of it getting a bath
thanks
steve

[IROC]

I would go with the factory recommended pressure as a starting point and then deviate from that only if you see a real need. You probably won't see a real need to deviate.

My car is similar to yours except I run either 245s/275s or 225s/255s and I run the same 29/34 recommended by the factory unless I'm at the track.

Mike

[Miguel Antonett]

For street driving I would put 30 & 35. For track use add 5psi to both.

[stlrj]

I noticed your alignment numbers seem to deviate from factory by a wide margin so why the concern that your tire pressures be at factory recommendation?

It would seem that the optimum street settings would include
alignment as well as tire pressures in an effort to be consistent.

Cheers,

Joe

[Cdnone1]

I'm not looking for the factory settings. I was just referencing the factory recommendations to use as a comparrision to what the alignment shop set them at. I'm really looking for the optimum preformance setting to maximize the heat , contact patch and sidewall deformation from my tires under street driving with the specs on my car
Steve

[steve911]

Steve--
40/42 sounds WAY high to me. I run 32/36 on mine and like the way handles. When I ran 29 in front it felt like the front end would breakaway real early.
My .02

[Cdnone1]

Everyone
Thanks. Steve 40/42 sounded way to high for me as well. The car only weights 2387 and is sprung harder
steve

[IROC]

My comment was based primarily on something a Yokohama tire rep told me once and that was that the factory (especially Porsche) puts alot of thought into the recommended tire pressures and you should really heed their advice *unless* you have drastically departed from the configuration for which the factory developed the recommendation.

IMHO, unless you have significantly changed the load on the tires (added/removed weight from the car) or are running tires that have significantly different load characteristics (bias ply slicks or some huge departure from a factory tire size), then the factory recommended tire pressure is a great place to start.

For instance, 29/34 works great on my car on the street (after all - you can't even come close to "limit" on the street anyway, so optimizing the pressure for street use is for the most part moot). Even wear, good, predictable handling, etc. Conversely, I found that 32/34 worked the best on the track (245/275 A032s).

You camber, spring rates, etc are all milder than my car and the 29/34 works great on the street for me.

Just my opinion.

Mike

[Cdnone1]

Thanks Mike
Thats the kind of thing I was hoping for. The car is substancely lighter and a little harder sprung (esp figuring in the weight lose) the tires are larger and the neg cam is different
Good predictable handling is really what I am after, actually the best performance I can get out of the tire under my cars setting
Your right about the limit and I do not act like the public roads are a closed track but I do like to drive "spiritedly" when conditions allow
thanks again
Steve

[RoninLB]

29/34 or 29/35 should be very doable. You can buy a temp probe instrument, not the IR type, and drive a straight flat road at hy speeds and they pull over and do 2 tires at a time to check a few things. Measure inside/outside/center between the threads. Repeat for a consistent reading.

fwiw.. 10F difference in ambient cold tire temps is about 1psi difference.