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-   -   Recommended Cabrio Tire Pressure (http://www.bimmerfest.com/forums/showthread.php?t=95947)

m3fest 04-26-2005 08:50 PM

Recommended Cabrio Tire Pressure
 
I am looking for recommendations for the ideal tire pressure for VERY aggressive driving.

Here are my specifics...

I will set the pressure first thing in the morning BEFORE driving at all and the outside temp is about 65 degrees.

I have the 19" factory rims with the Conti tires

The rear tires have about 10% tread left and the fronts 30% (I am waiting for a set of back-ordered PS2's to come in).

NO rain driving
NO passengers
Outside So. CA temps right now are around 70 to 80 degrees

I am looking for maximum cornering ability and minimized under-steer.

Thanks for the help!!!

dawgbone 04-26-2005 10:41 PM

Quote:

Originally Posted by m3fest
I am looking for recommendations for the ideal tire pressure for VERY aggressive driving.

Here are my specifics...

I will set the pressure first thing in the morning BEFORE driving at all and the outside temp is about 65 degrees.

I have the 19" factory rims with the Conti tires

The rear tires have about 10% tread left and the fronts 30% (I am waiting for a set of back-ordered PS2's to come in).

NO rain driving
NO passengers
Outside So. CA temps right now are around 70 to 80 degrees

I am looking for maximum cornering ability and minimized under-steer.

Thanks for the help!!!

Weird question...

As far as the stock Contis, as well as stock suspension setup...Look inside the driver's side door..BUT, with 10% tread(rears)...I would deflate them to 10psi less than what's on the sticker..Or replace them quickly(they go fast, once signs of good wear)...As far as the fronts, swap left from right..

If the car is stock on all suspension components...It's a good idea to keep the understeer..The car has been tried and tested for those tires and tow/camber...Despite the overwhelming tilt/lean, the car actually will pull nicely out of corners with a stock setup..But you need to specify, not temps of SoCal, but what you are trying to do with the car...You might need something more than tire PSI....$$$

m3fest 04-27-2005 12:44 AM

Thank you!!!

I may have been exaggerating the wear...I only have 8,000 miles on the car so I know I could get at least another 2 to 3 thousand miles from the rears and even more from the fronts.

I am certainly aware of the OEM recommendations 33 F & 35 R but I am also aware that whatever they are recommending is based on a pressure that is a balance between grip and comfort for people that use the car as a daily driver.

However, based on the fact that I am NOT interested in comfort and strictly use the car for aggressive driving under the conditions I mentioned above, and NOT as a daily driver...I was really interested in what pressure would give me the best grip with the stock suspension, tires and wheels.

I guess even more specifically, I currently run 36 F & 38 R and have heard that if I were to run 38 or even 40 all around it would improve the cornering and reduce the under-steer further?

I was also told that the tires are directional and should NOT be switched from side to side, as a matter of fact I'm pretty sure the sidewall has an arrow identifying the direction the tires should be rotating? And even if I could rotate them I don't see any benefit since the wear on all 4 has been EXTREMELY even and consistent.

Pinecone 04-27-2005 02:28 AM

I would NEVER inflate the tires to less than factory specs. You are asking for a blown tire, at speed.

For street driving, raise the pressures. Most tires need pressures in the mid 40s or higher to maximize performance. To tune, you need to reduce rear grip to balance lack of front grip.

As a starting point, for most drivers I suggest 2 - 4 psi more all around, then another 2 - 4 psi or so in the front to reduce understeer. So rear goes from 35 factory to 37 - 39. Front goes from 33 factory to 37 - 41. Then play with pressures.

Or just pump them all up to the maximum pressure on the sidewall, then lower rear to reduce understeer. But with stock tire sizes, you will not see much reduction in understeer. So just plan on 265s all around when you replace the tires.

And next time, if you are looking for maximum performance, get a Coupe. Lighter and more torsionally stiff


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