Recommended Tire Pressure After Switching Brand

[sinbad]

I just replaced my oem 18" Continental ContiSport with Michelin PS2 on my '00 S. I used to keep the pressure 29 front and 36 rear as per manual which gave even wear. What pressure should be PS2 be set at. The tire installer advised me to increase pressures since PS2 has a higher minimum pressure than the ContiSport. Bascially, the minimum pressure difference must be added to compensate. I don't know the minimum pressure for either tire, so I call upon you guys for for guidance.

[mee]

I think your tire installer is giving you BS. I've run a whole range of tires on my Y2K Boxster S, but not the PS2s. With stock sizes, I have found the front tire pressures are laughably low and the rears about right or a hair high. I would try 34 all around and see how you like it. Then fine tune +/- 1-2 psi per your liking and tire wear. The ContiSports are absolute garbage. With the PS2s and the right tire pressures, you will feel like you have a new car.

[4agdtym]

Well, I have another opinion.

Tire pressure is more a function of driving style combined with tire size, than a function of tire brand. Depending on different desired goals, you would use different pressures.

I enjoy the spirited drive and I auto cross regularly. If you look at the tire sidewalls, most tires have indicators that are a guide for setting tire pressure to maximize tire performance for cornering and acceleration goals. Usually the indicator looks like a little arrow, diamond, or some other figure that sits just about a the point where the tread meets the sidewall - there are several indicators evenly spaced around the sidewall of a tire. I'm not at home with car and camera or I would share a photo of the indicators on my tires - Yokohama s-drive (an inexpensive tire that wears relatively well, has decent grip, and a very economical price - not for top-end high speed track use).

I set the pressures so that the tire shows wear just at the point of the indicator when driving very hard in corners - even driving at the point where traction begins to get lost. If the wear goes beyond the indicator, I need more air; if the wear doesn't reach the indicator, I need less air. For my tires (225/45/R17 front and 255/40/R17 rear) it works out to about 33 front and 36 rear. When I used the factory size tires on the front (205/50/R17), I used 29 front and 36 rear - the recommended pressures from the factory regardless of tire manufacturer - (I believe).

If you are trying to maximize gas mileage, you probably want to run the tire a bit higher in pressure to reduce rolling resistance (or you might just want to buy an economy car). Still, the pressure is likely to be different in front and rear due to the different tire sizes front and rear.

Too much air will reduce cornering performance and/or decrease traction during acceleration - and cause increased wear along the center of the tread. Not enough tire pressure will reduce performance and reduce tire life due to increased heat created in the sidewalls as they flex during rotation (and increased wear at the edges of the tread pattern).

Hope this helps.

David

[70Sixter]

You can use white shoe polish as an indication of how far the tire is rolling over. My opinion is that 7 psi is too much pressure differential and it is specified to keep inexperienced Porsche drivers from getting into trouble. I think 4 psi difference is about right for spirited driving by a competent driver..

[geoff]

When I switched from the original ContiSports to the Pilot Sports on my '01 with 18" wheels, the Porsche specs said to keep the tire pressure the same at 29/36 f/r. Porsche specs are set up to achieve enough understeer so you can't get into too much trouble and sue Porsche for your own stupid driving. I found 30-31 PSI in front and 36 in back is a good compromise. All the Porsche sports cars seem to be happy with the rear tire pressure a bit higher than the front. Depending on how long or many miles since you last had a 4 wheel alignment, you might want to consider that before you start messing around with tire pressure (especially considering the price of replacing tires because of excessive wear).

If you want to get overly obsessive about tire pressure, you can get one of the infrared laser electronic thermometers and read the temperature across the width of your tire after a spirited drive and adjust your tire pressure until you get a consistent reading all around. I haven't tried this but was told a lot of the autocrossers do this to figure out what tire pressure to run. I just drive the car and enjoy it without over analyzing.

I found the Pilot Sports to be so vastly superior to the ContiSports it wasn't even funny. The PS2s are supposed to be even better still.