Jon Schepps

I have a new-to-me '99 996 and I'm experiencing tremendous tire wear on the inside edge of my rear tires. All the wear is limited to the inner 1 inch of the tread. Rear camber is -2.5. At first the toe-in was set to about 1mm per side and both rear tires (Hankook Z214s) went down to the cord in 4 DE days (1st photo). I then reduced the toe-in to near zero and threw on some used, but good, R6s, and one side showed what looks like rips or gouges in the outer edge - down to cord (2nd photo). My previous 996 with almost identical components, did not do this. Any ideas what's going on?

garrett376

Do you have limited slip; if so is it shot? If you run tight corners with no LSD and "burn out" the inside wheel in corners as the car leans, this can occur. Just a thought....

Jon Schepps

It (allegedly) has a Quaife LSD. Is there a way to test it on the car?

himself

What pressures are you running. Almost looks like under inflation to me.

-td

jrgordonsenior

I assume (not knowing much about TBDiffs) you can jack up one side and see if you can easily turn the wheel in the proper direction. Are you spinning the inside tire on acel?

Are both rears cording on the inside? If so I can't help but think something's worn out or broken. I would ask the shop that did the setup to check all the bushing,etc. for play or damage. Also maybe get a 2nd opinion on those alignment settings.....

Last thought, used tires can wear based on their previous use. If everything checks out OK then try a set of new R6's and see what happens....

Jon Schepps

I ran 40psi for the Z214, 36 for the R6.
1000# springs.

On NJMP Thunderbolt, with 1mm toe-in, both rears wore about the same, maybe slightly worse on the left.
On NJMP Lightning, with near 0 toe, the left was way worse. This track is known for wearing the left side tires, but not this much! The tire in the 2nd photo was on the LEFTside. If it was wheel spin, wouldn't the inside (predominantly right side) tire get the brunt of the wear?

Its possible that its due to the used tire, but that would be quite a coincidence.
I actually went through 2 sets of rear Hankooks. The first was with the stock upper control arms (dog bones) and toe arm. Although they had no signs of wear, I replaced them with spherical bearing arms. Re-aligned, then went through another pair of Hankooks in a few of days. Thinking that maybe the Hankook shoulder construction just didn't work well on the 996 rear, I threw on the R6s and took out the toe to see what would happen. Not much different. So I'm hesitant about putting on yet another new set until I find the cause.

I've seen threads about excessive inner tire wear on the 996, but these were mostly for street cars with stock suspension that had more than stock camber and toe to improve handling. No surprise that would wear the insides in 10K miles of street use.

If you look at the R6 (2nd) photo, the tire looks more like its gouged than worn. This was after just 3 20-minute sessions. Maybe due to excessive heat? But why?

Ritter v4.0

Looks more like rubbing that wear. It's not rubbing on the inside somewhere?

onefastviking

Motons - check canister pressures, check all **** settings to be sure none have walked or moved positions.

Agree with JR, check all bushings, especially the thrust arm bushings. Older bushings could be weak enough to allow the play causing the dynamic alignment to be much further off (toe) than you think you are set at.

Jon Schepps

It sure looks like its rubbing, with a very fast transition from very worn to not worn, but there's nothing that's even close.
Will check thrust bushings. Cannister settings and pressures were set between events, but will check again.
Thanks.

fstockcarrera

+1 on rubbing a control arm? Even a 5-10mm clearance can rub when the tire carcass deflects under hard corning. Space out the tires as much as possible. Loose rear control arm ball joints will allow excessive Toe changes. Check all suspension components.

spare tire

Your photo is taken at droop with rear tire off the ground. ( so as to fit camera?) Your dog bones and toe links appear to be hard heim jointed without rubber. It looks to me like a rear toe problem. Too much toe. OR excessive wheel spin in a straightaway when the suspension is NOT loaded. the negative camber you are running places only the inside edge of the tire on the ground when you are not cornering. Have you stomped the gas pedel in 2nd gear. The wear seems very evenly distributed around the tire. Are locking plates installed where toe links connect to car?

Jon Schepps

Correct - heim joints on upper control arms and lower toe arm - all new. Toe arm has locking plate. Solid thrust arm bushing on the lower control arm, rubber bushing on the chassis end, but seems in good shape. No wheel spin that I'm aware of. If its rubbing, I would see some evidence on whatever its rubbing against, and there's just nothing there.
I'll recheck the toe again.
Thanks-

Jon Schepps

Had the alignment rechecked and it was off quite a bit. Don't have the numbers handy, but too much toe in and uneven camber left to right. Reset it, checked and re-checked. After about 7 DE sessions, the rear tires looked OK.
Then one side went flat. I discovered 5-6 small slashes in the inner edge of the tread, perpendicular to the edge. Same area as where I was previously seeing the excessive wear. But these were discrete slash marks, so I'll chalk it up to coincidence, although I have no idea what could have caused these cuts.
So for now, I'm calling the excessive wear an alignment problem.
Thanks for your input,
Jon

Ritter v4.0

I stand by my original thesis.

Jon Schepps

I doubt its rubbing. The cuts are in the tread, perpendicular to the rotation and appear only in a few discrete places. But admittedly, I don't know what caused them.