Tire Pressure ??

Large tires and light cars, what air pressure do you use ??

I have Bridgestone 185-65 on front and 205-60 on rear,
what pressures would you recommend ??

Thanks Jerry

ps, we have a (James Dean painted) Spyder in Zanesville, OH
hear that it came from CA but I haven't found out who has it yet

I am run around 20psi...try different pressure and drive it...

This has been discussed here before and it seems to be related to driving style and personal preference. 24-26 PSI seems ideal for my car and style of driving. Any lower and the handling becomes "sloppy." Any higher and it's "skittish."

TMc

Thanks, I was wondering how low to go as mine still feels skittish with 28 front & 30 rear.

Some guys are as low as 15 f 18 r. Experiment and remember, a bug (I believe) called for 18 f & R with skinny tires. My car felt skittish with 24 f, 27 r. I am down to 18 and 22 now, and it feels pretty good.

I'll keep lowering the pressure and see what hapens.
It may also depend a lot on how stiff the tire sidewall is.

I'm running 23psig front and 25psig rear. Wear pattern is good and I'm getting excellent road holding.

This is what the Porsche Spyder 550 Drivers Manual says:

For normal driving

front 1,4 at

I dropped my pressure down to 20 pounds both front and rear just as a test. Under heavy cornering there was enough sidewall flex the car was at best "strange". It would move perhaps 2 or 3" sideways from left steering direction to right. It was not safe in my opinion. I am running 185/60/15 Yokohomo on the front and 205/65/15 Yokohomo on the back. 4.5" rims on the front, and 5.5" on the back. At 28 pounds it handles more as I expect. I have tried lower in the front, say 24 pounds, but I am happier with 28 on all 4 for just driving around on the street. I have also tried pressures as high as 32 pounds but the car does not stick well at those pressures. Braking in particular is poor.

Axel, I don't know I would pay much attention to the factory manual as those were bias belted tires, no?

Just a guess, but I would expect a wide range of pressures to be optimum on different cars......

Jim

Jim,
you are right. There are too many different possibilities as to tires and rim sizes.
Still on a 165/15 radial on 4,5" rims the pressure 20/23 works reasonable well for me. I have tried different variations, my main concern is the tendency of the car to oversteer.
Would a front swaybar improve this situation?
Axel

My only other experience with a mid-engine car was a 72 Pantera and the rear sway bar had a lot more controle over understeer and overall handleing than the front bar.

OK, here's the deal:

To increase understeer you want to do the following:

Lower front tire pressure
Smaller tires on the front
More positive front wheel camber
More negative real wheel camber
Stiffer front springs
Thicker front sway bar (or add one)
Move weight forward

Remember to just try these one at a time and see how you like it.

Also, to increase oversteer just do the opposite.

Thanks Bert,
I will try it.
Axel

After tryin several different combinations my spyder with 185x65x15 front and 205x60x15 rear at seams to like 20psi front and 24psi rear, any less and you can feel the sidewalls flex.

And the more pressure you go in the back, at least for me, the less oversteer. I like 6 pounds difference right now, although I did have a rather loose run last Sunday autocrossing. Well, couldn't have been the driver!