befast

I am trying to evaluate a used set of wheels and tires. Could someone double check my reasoning on evaluating tire use?

Tire usage % = current tread depth / (new tread depth - minimum tread depth)

I am using 2/32" as minimum tread depth, at which point tires are considered worn out. Also, a tire should be passed on if it it's been fixed for holes, or has any kind of physical damage, uneven tread wear. Anything else to consider?

Ubermensch

Sounds about right, although the term "tire usage" suggests how much life has been used up while you're actually calculating how much tire life is left. Slightly uneven treadwear isn't a big deal as long as you're considering the lowest spot on the tire as your 'current tread depth' in your calculation.

Carrera Mike

Well Befast, make sure you're measuring on the inboard threads of the rear tires. The rears wear out way significantly fast on their inboard side(for the 996).

Regarding the measurement, if you look at the brand/model of the tires you are looking in buying at tirerack.com, under the "spec", it will have the thread depth of the brand new tires in 32nds of an inch. divide that by a 15000 mile life span for the rears, and you could find out how much you could still use out of what you want to buy.

Also, I've heard that Z rated tires are supposed to be significantly degraded if patched. ( I have two on mine, so that speaks for my belief. Of course I wouldn't run those on DEs.

Riad

My tires are worn out when you can see the steel belts.

67FJ45

Carrera Mike,
I'm on my third set of rears on a 2004 C2, and the first two sets wore evenly across the tires. For the third set, I've actually had more negative camber introduced to improve track performance, so maybe that will change the street tire wear (I use a separate set of track tires). What did I do wrong on the first two sets to get such even wear?

dirtrack49

I might consider a used set of tires for the fronts only since they last me nearly 20k miles. As far as the rears, they are down to the wear limit in 6000 miles or less so buying used ones would be a waste of time.

I have wondered why my tires wear out faster on the right side of the car versus the left??? When I replace the rears, I can be down to the wear limit in 5000 miles and still have at least another 1000 miles to go on the left rear.

I also have wondered since I don't really get on the car out of the hole, why these tires (Pirelli P-Zero's) wear out so fast? Albeit, all of my driving is on canyon roads. No freeways and very few straights.

Tom L
2002 C2

Ubermensch

Uneven wear (side to side) or across the tire is a matter of alignment. I tend to get even wear because I don't run agressive camber but more importantly I made sure to key my toe settings near zero.

Carrera Mike

Hmmnnn, oh I forgot to mention that my car is lower than stock by an inch. I'm sure that its that lowering that caused the rear camber to be more on the negative side hence the wear on mine are more on the inboard side of the tires.

gregorycarl

Consider every 2/32" to be approximately 25% of the useful value of the tire. 2/32 worn to the point of replacement. Average tire performance tire is 10-11/32". So reasoning would be: Tire has 4/32" (25%), 6/32" (50% left), 8/32" (75% left), 10/32" (100% left).

Don't forget to factor in the cost of mounting $13-$25 a tire.