Quadcammer

Hey gang,
Have about 16k miles on this set of Sumitomo HTR Z3 rears.

Obviously I have a bit more negative camber than stock and also have a toe out of alignment, hence you get the cording on the inside with plenty of tread along the tread face.

What is new to me is the cupping on the inside. The drivers side doesn't have this.

Worn shock or control arm? I have a bad rear sway bar bushing, but the rest of the suspension looks pretty good from a visual inspection.

Any input would be superb. thanks

LexVan

Oliver, what tire pressures? Actually 16,000 miles on a rear set of tires for a 993 is not too bad. I could never get much over 12,000 on Kumhos and Yokos. IIRC, my passenger tire took more wear & tear than the drivers side.

This has been debated before, and I forget the consensus, but on low profile, boxy tires, tire pressures play an opposite relationship to PSI and cupping.

Quadcammer

I agree, the life was great.

I run about 37psi cold.

LexVan

Does the passenger tire take more abuse because we drive +90% of the time without a passenger? The way the rear diff applies power to the rear wheels??

Ever thought about dismounting your tires 1/2 way through a life cycle, remounting and flipping sides to extend performance and tread depth a little longer?

37 might be 1-2 PSI low, but I know why you do it. Still, 16,000 miles is great, hard to complain.

pp000830

Read this:
"Cups or scalloped dips appearing around the edge of the tread on one side or the other, almost always indicate worn (sometimes bent) suspension parts." I also found this problem is more prodounced with certain tire block designs and with harder tire compounds.

Quadcammer

yes, I was hoping for some real life insight on things on the 993 that might cause this.

bw993

Rear alignment issue. Looks like one side is toed out and the other is toed in.

PRSWILL

Had this happen on another car- my Acura- so not 993, but came down to an alignment issue and bent control arm. Replaced and the issue went away. The Alignment guys missed it too as it doesn't show up until the car is moving.

Quadcammer

interesting.

how can you tell that?

AOW162435

How can you deduce that from one pic of a corded tire?



Andreas

bw993

I had the same issue/wear pattern on 2 sets of tires on my 993 and my alignment was the problem. If you have an alignment with increased negative rear camber your total toe-in should be 0 to 1/8. If you do not have the toe-in equal on both rear tires you get cupping on the inside tread of the tire that is less toed in.

NYC993

Also iirc, the kinematic toe corrects the toe out on outside and to toe in on the inside in a turn to staighten out the rear wheels. So if that is off, you can have too much toe-in turning one way but not the other. I must admit that the whole kinematic toe is beyond my alignment knowledge, but it does affect the toe and the wear if nit set properly.

fatmike

I'd be thrilled with 16K miles out of my rear wheels: cording, cupping and all.

Why touch the alignment to fix a problem that really isn't?

/

Cactus

+1! I'm lucky to get 10K but I have the same wear pattern so looks normal to me.

AZ Targa

+1, I'm surprised that it took so long to find this problem.

How often do people check their tires? I tend to give them a strong inspection every 2-3K miles by measuring tread depth across the tire (mm or 32) checking for cupping, separated belts, bubbles, punctures, and uneven tread wear in general.