Hello,

I've only owned by '05 C2S Cab for a couple months and I recently noticed that my back right tire has becoming a racing slick while the back left tire is about at the wear bar (Bridgestone Potenza 295 RE050) Does anyone know why the right tire would wear faster than the right? I never noticed before because I only looked at the driver's side tire and assumed they would be the same.

Also, I reached my hand in on both and felt metal on the inside edge of the tires, much more on the more worn tire. Obviously, this is a sign of tire that has been on way too long, but is it also a sign of something else? This completely freaked me out and feel lucky not to have had a blowout or other.
I'm having 2 new ones installed tomorrow AM, which can't get here fast enough.

Any insight would be appreciated.

 

Time for an alignment?

 

Welcome to the world of 911 tire wear. With so much weight in the rear, and the amount of negative camber dialed into most 911's, rear tires lead short lives. For street driving, typically the front tires last twice as long as the rears, which means you replace the rears (which cost more, naturally) twice as often as the fronts.

The fact that one rear is wearing more than the other points the finger to an alignment issue. You should certainly have the alignment checked when the new rear tires go on. Uneven camber or toe in/out between the two rear wheels could account for the problem.

For future reference, keep in mind that rear tire wear on a 911 can be very deceptive. The outside edge of the tire may be perfect - the tread depth may look great for almost the entire width of the tire - and the inside edge of the tire may be down to the steel cords. I think most 911 owners have experienced that at one time or another. Learn to get down on your hands and knees, use a flashlight if necessary, and check out the inside edge of your rear tires at regular intervals.

How long the tires will last depend on your alignment settings and driving styles. I've gotten 20K miles on a set of rear tires on a Carrera, with very conservative alignment and zero track days. I've also corded a set of rear tires in 2700 miles with several track days included in those miles. "YMMV" was never more true than in this context.

DMoore
'11 GTS
'10 Panamera 4S

 

DMoore, thanks for the time and great info. I'll be sure to have them check this. Love your garage...

 

Also note that lowering a car can result in uneven wear, based on limits of stock suspension adjustability. That's why many will buy a rear toe link kit from RSS, etc.

 

are the tires properly inflated? if so and the L&R tires have equal mileage, the alignment may be off.

 

In normal driving the right rear tire always wears faster on cars with rear-wheel drive. It's a routine effect of the differential that splits the torque between the two drive wheels.

If the difference is remarkable, that just means you're passing more torque through the differential than would be the case with a... oops. Ran out of examples. I don't think any cars with low power have rear drive these days. Well, your car is delivering more torque than say my VW from 1955 or my MG from 1965. And that's hardly surprising with a Porsche Carrera. Hell, it wouldn't have been surprising in 1965, let alone with a modern Carrera.

Because of that effect of the differential, it is fairly easy to spin the right rear wheel and I could do it on that 1965 MG with a rousing 65 hp. Every time we move away briskly from a stop, or even accelerate from slow cruise to pass someone, the torque is unevenly divided between the drive wheels and that creates more wear on the right rear tire. This is the reason that in low traction situations, the car swings the tail end to the right if you overdo the acceleration. (Limited slip differentials don't cure this. It's built into the geometry of the differential gears. They just limit the problem.)

Incidentally, that pattern of wearing the inside faster is routine as well, for the reasons DMoore explained. Suspension adjustment is an all-night discussion, but the bottom line is that performance cars always do that in road driving because straight line wear dominates over the corners and the car is set up to handle well in corners. For track work like DE days, people run around trying to find ways to get their suspension adjusted even further in the direction that causes that wear on public roads because on a track the corners dominate the straights.

To even out the wear across each tire's tread, you'd have to move to the end of a very twisty road, which could be fun come to think of it. Or you could adjust the suspension to give up the handling, which would not be fun.

To even out the wear between the drive wheels, you'd have to strangle the engine back to the 40 hp of my 1955 VW. I had fun with that car, but not because of the power so I can't recommend this approach either.

Basically, it's a powerful sports car: expect the inside edges of your tires to wear fastest, the rear tires to survive only half to two-thirds as long as the fronts, and the right rear tire to wear out fastest of all. In a very old saying: "Sports cars eat rubber and **** speed."

Gary