caronsd

I've got a question - perhaps it is a known phenomena, but I would appreciate learning from the collective Rennlist brain trust....

I pulled the wheels off my Spyder today for cleaning and noticed significant uneven tire wear on the rears. The car has about 7500 miles on it - all street driving. The tires are the Pirelli P-Zeros. What I see is that the center section of the tire is at the wear bars while the inner and outer edges show significantly less wear. Kind of the classic "over-inflation" scenario. I just checked the pressure of the rears with my digital gauge and they're both at 31 psi - right at the factory recommended numbers.

When I pulled the fronts, they looked fairly even across the tread.

Anybody seen this? Any ideas as to the cause?

Thanks!

Polarporsche

I only have about 4000 miles on mine but rear tire wear looks pretty even so far.Mostly highway miles and I keep a close on the the tire pressure.

On my 2007 Boxster S I got about 14000 miles on the rears and they were done but the front tires were still great, my right foot is a little heavy.

Plavan

I have the Michelins on mine. I just turned 5K miles on her and they look even.

jimcabc

After I picked up my new Boxster, just the base car and not a Spyder, the salesman said to expect maybe 12k or so on the rears, 20k+ on the fronts. I don't have enough miles on the car to know myself.

No HTwo O

Are you sure your tire gauge is accurate? 7,500 miles is not bad tire life. Do some research here on Rennlist. The wear you are indicating may be UNDER inflation, not over. I remember reading some old threads in the past, that with our low-low profile tires, and wide footprints, the over/under inflate wear was counterintuitive.

31 PSI in the rear seems very low. Are you sure this is right? My 987.1S with 19" wheels is 37 rear and 32 or 34 front OEM spec. Why is the Spyder so much lower? Thanks.

BostonDuce

Spyder tire pressures are lower than the regular Box's by about a pound due to it's unique suspension set up.

Although I don't have the same brand as the OP, I suspect we're seeing the results of the "N-Spec" effect. My Goodyear F1's are like gumballs the rubber is so soft. I can scuff off rubber by just rubbing my thumb across the tread.

BD

Byprodriver

Hard acceleration from stop or over inflation. There is no other way.

Macster

Early on in my 02 Boxster ownership I encountered this rear tire center wear.

In short, it is normal.

A longer response is that I at first suspected overinflation and dropped tire pressure down a couple of psi. Over time this didn't seem to help so I suspected tire growth at 'high' speed.

This was based on the fact alot of my driving involved interstate driving at legal speeds which I assumed qualified for high speed.

It does not.

What qualifies as high speed driving is what one can do legally driving on an unrestricted autobahn at speeds way in excess of 80mph (the highest legal interstate speed in the USA).

But before I came to realize this I bumped the tire pressure a few psi over the recommended inflation pressure to keep tire growth from happening.

What I found is with the rear tires (might add I've run Pirelli and Michelin tires on the Boxster and the Turbo shows the same tire wear pattern and I've run Continental and Bridgestone tires on the Turbo) inflated to a few psi below or at or above the recommended inflation pressure the rear tires wore in the center more than the edges (unless the alignment was off which then resulted in extremely accelerated inner edge tire wear).

More agressive street driving seemed to exacrebate the rear tire center wear phenomenon. For USA cars, it also tends to cause the right rear tire to wear faster than the left rear tire.

My advice is to be sure you have an accurate tire pressure gage and use it to ensure the front and rear tires are properly inflated (cold) to the recommended inflation pressures. I use a dial gage to get the inflation pressures at the same reading. This is not hard to do with a good tire pressure gage.

Also, be sure the alignment is spot on. There is also the factor of the car's default alignment settings which may result in some handling benefit at the expense of accelerated tire wear.

Then drive the car.

Depending upon how you drive, you may find tire life under 10K miles. Depends upon how 'hot' you like to take sharp turns and how much throttle you use. These cars (most anyhow) do not have LSD so the inner tire will spin under hard cornering/hard acceleration events. You may not feel it but it happens.

If you drive a bit more conservatively you might expect to see 12K, 15K, 18K maybe even 20K out of the rear tires and FWI at least twice this mileage out of the fronts.

The front tires based on my experience can last a long long time but they get hard from the heat cycles and become noisy and less grippy so I change the fronts regardless of tread depth every 2nd set of rear tires.

If the tires show uneven wear -- mainly one or both rear tires wearing their inner edges faster than their outer edges, but pay attention to the front tire wear too -- I'll have the alignment done.

Invariably the before and after printout shows the rear toe was out.

Sincerely,

Macster.

MikeBat

Interesting stuff Macster!

So why am I almost cording my fronts on the outside edges? I track the car and have as much negatve camber as I can get up there.....

I think I need more negative camber up front!

Rears wear evenly across the tread.

No HTwo O

You're driving in reverse too fast.

Macster

Generally outside or inside tire wear at the front is a toe problem.

First I would ensure the alignment is correct. You can dial in more negative camber if you want to of course -- many tracking owners do this -- but be sure the toe is set correctly. Now there may be a better toe setting than the factory recommended setting which helps address outside tire wear when the car is used predominately on the track.

Next time you're at the track walk around and look at front tires of various cars and when you find a car with front tires with no wear or inside or outside edge wear ask the driver what alignment settings he runs. Try to develop a correlation between what the observed tire wear is and what alignment settings are being used.

You might find someone who has hit upon the best alignment setting that provides even tire wear.

OTOH, on the track where very high cornering loads, coupled with hard braking and the tires reaching high operating temperatures during all of this, there may be no ideal alignment setting.

In order to provide the feel the driver likes, the alignment may be set in such a way uneven front tire outside or inside edge tire wear is just going to happen.

Sincerely,

Macster.