I found this on the inside of one of my rear tires yesterday and know that it would be unsafe to drive at high speeds. So, clearly, I need at least one new tire. However, I have read that one has to be careful not to have different diameter tires so as to ruin the four-wheel drive system differentials. So, my question is, given that my other rear tire has some life left in it, do I need to buy a whole rear axle or can I just replace the one broken tire? Alternatively, if both rears are replaced, am I now too far away from the front tire diameters and need to replace all four?

I read on Renntech that all tires needs to be within 2% of their circumferences. Using this information, an assumed worst-case scenario of 4/32 depth on the good rear tire, and the tire manufacturer's website to determine the diameter of the new tire, I have arrived at the conclusion that just getting one replacement tire would only cause a 1% difference between circumferences. Thus, I should be fine just getting one replacement tire.

Comments?

 

From everything that I have read, there is a 4% range of tolerance. I would get 2 new rear tires. Usually the fronts last twice as long as the rears. So 2 sets of rears for every set of fronts.

 

Since it is a Porsche, just go with the most expensive option.

 

i would replace the 2 rears, and keep the good used as a spare if you need one in a pinch. like mentioned in previous posts the rears will wear twice as fast as the fronts. so when you need another 2 rears you can get 4 new tires and perhaps try a different brand if inclined.

 

Agreed, If the fronts are good...do two rears same brand, etc. The 4% difference is really a front to back number so not really an issue here. Significant wear right side, to left side rear, would possibly affect handling and alignment....but just guessing....and how much difference could be tolerated, don't know?

 

Two rear tires replaced. The guy who installed them found a small dent in the inside lip of one of the rear wheels at the same place of the tire bubble. You can't tell from the photo above, though. The newly installed tire + wheel passed balance test, and I've been advised that minor tweaks like this at the inside lip don't affect much, but it still irks me. I've tried to be exceedingly careful for potholes and going up/down curbs very slowly and at an angle. I guess it doesn't affect the ride much because I got it up to a decent speed on the ride home with no bumpiness. Shrug.

Thanks for the advice.

 

If you want to ruin your day, get a Hunter 9700 Road Force Balance... minor dings in rims, inside OR outside, can cause the assembly to fail run out or roadforce... Generally they'll be OK to drive on, but not perfect. Good news is that an inner rim ding can be 'fixed' without worrying about the finish.

A

 

Did you get a 4-wheel alignment? I'm in the same position and I was told after I replace the rear tires that I'll need an alignment. Seems with the cost of the alignment ($300-$500), I should just get 4 new tires and do the alignment instead of just 2 rear w/alignment and then have to do it again when the fronts wear out (in a year or so).

 

Nah, the alignment is fine. It lists a little to the right ever since I got it, but nothing that bad. No need to do it in my opinion. If more issues with potholes pop up I'm just going to put 17s on them with giant sidewall tires and be done with it!

Yeah, they told me that little dent can be fixed pretty easily and at low cost. If I wanted to, I could have Work replace just the inside piece of that wheel, but that would probably cost 3x as much as just getting it fixed.

Now I'm paranoid even pulling into my driveway where the entrance is pretty narrow and I general roll one tire or the other over a couple inches of the curb on the rear wheels going up or down at like 2 mph. Lol if that causes problems I'm screwed.