Correct PSI for Pirellis
 

I'm trying to ascertain the correct tire pressure for the tires on my Boxster. On front are Pirelli P Zero Rossos 225/40 ZR-18 and on back are 265/35s. The Boxster owner's manual says the PSI for the fronts should be 29 and 36 in the rears. Checking both the Pirelli web site and Tire Rack's specs, they both recommend 51 psi. Any input would be appreciated.

Thanks.

Follow the tire pressure recommendations in your owners guide.

Shouldn't you follow the PSI recommendation that is printed on the tires ?

I have the same tires in the same specs as you as I use 29 PSI in the front and 36 PSI in the rear. No problem at all!

The car's manufacturer sets the tires pressure that is best for that specific vehicle.

The pressure on the sidewall and the TireRack spec are max pressure, not recommended.

Go with the owners manual as it is for the specific vehicle and tire size. I go with 30-36 or 29-35 cuz it feels better to me.

bmussatti,

Ok, now I am confused...

I have 265/35ZR18's on the rear.
Tire says max pressure 50psi.
Owner's manual says run 36 psi.
I am currently running 42 psi.

I have 225/40ZR18's on the front.
Tire says max pressure 44 psi.
Owner's manual says run 29 psi
I am currently running 36 psi.

Are my tires over-inflated ?

Also, looks like U of I and Northwestern got beat up pretty bad yesterday :mad:

At least the Bears are beating the snot out of the Packers :D

Did you get my PM about AutoX next weekend ?

Hey Nick:

I think your tires sound like they are over inflated. I think you should run them closer to the owner's manual pressures, and then make 1/2 pound to 1 pound adjustments at your next AutoX event, and dial the car in for the best balance between over-steer & under-steer.

Also do an "advance search" for this topic with MNBoxster at the poster. He listed a pretty interesting formula for tire pressures. If I find it, I'll post it again soon.

Yes, Illinois and Northwestern looked aweful yesterday. But, I like it when the Wildcats get beat. It uspets by father-inlaw and brother-inlaw....and that is very enjoyable to watch. I just wish the Irish got beat too!

No autoX for me next week. Too many Octoberfest Parties on the family schedule...2 in 3 days! :)

Nick, read this thread from MNBoxster:

http://986forum.com/forums/boxster-general-discussions/5353-tyre-pressure-boxster-poll.html?highlight=formula

Hi,

As mentioned go with the Manufacturer's recommendation, but play around 1-3 PSI depending on your tatste, driving style and road conditions.

The sidewall values are the MAX values which you should run the tire, but not for every application. The Tires are not model specific, but are sold for any number of models and makes (consequently weights and loads).

The Porsche recommended pressures are not absolute. Porsche determines this PSI using many criteria including maximum load (if you never have a passenger, a little lower pressure won't hurt), ride comfort, ease in parallel parking, etc. The value is the best compromise they could come up with. If you live in an area with poor roads (cracks, potholes, etc.) you may want a few more PSI to avoid damaging a rim should you hit a pothole. Likewise if you enjoy a little firmer ride or live in a Wet climate (the harder tire will channel water better, but only 1-2PSI!!), also if you're a long distance interstate driver because you'll maximize MPG.

Varying 1-3 PSI won't blow up the car or put the Tires through undue wear and tear. Learn to read your tires too and if overinflated, wear will be more prominent in the center of the tread, more so on the outside if underuinflated.

In general, underinflated is worse than overinflated (within 1-5PSI). Remember the Ford Explorer? All affected cars were on underinflated tires. This was more responsible for the trouble than the make/manufacturer of the Tire, but this was no good because it left no one for the lawyers to sue, so they went after Firestone...

Happy Motoring!... Jim'99

bmussatti / MNBoxster,

Thanks !

Nick

Thanks for all the info everyone!