Dumb 308 rear camber adjust question:

Ok, this seems obvious, but I just want to be sure:

My rear left tire is wearing too much on the inner tread. The other 3 are wearing evenly.

Too much negative camber. The proper way to reduce this negative camber is to remove a shim or two from each lower inner control arm fork, correct?

I know some of you will suggest that I take the car in to have it professionally aligned, but here are 2 reasons why that's not practical right now:

1) the car is currently up on 4 jack stands with all shocks removed--my Varishocks leaked for the 3rd time, and they are shipped off for rebuilding (warranty).

2) I had the car aligned last year, the other 3 tires are wearing normally.

I just need to know for sure I'm doing this right, while the car is in the air. It seems obvious that to remove a shim will draw the lower control arm in, reducing negative camber.

Am I correct?

Thanks,
Greg
77 GTB

 

Yes (remove an equal total amount of shim from each mounting fork to not change the toe-in)

 

Thanks Steve, good to hear from you!

Greg

 

Are you sure it's neg camber? usually rear toe in wears tires much worse than neg camber. I know it doesn't make logical sense, but it really is true.

 

The wear on that tire is on the inside 2". Wouldn't that be caused by negative camber?

Would too much toe-out cause the same result?

 

Excessive toe-in at the nominal negative camber and excessive negative camber at the nominal toe-in both work to wear the inboard tread area. If you park on a reasonably flat surface and just eyeball the two rear tires from behind the chassis, or use a framing square, you should be able to detect if they are significantly different in camber (i.e., touch the framing square to the bottom tire sidewall so D=0 and measure/compare C on each side):
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For something significant enough in camber to cause a notable wear difference (like ~1 degree), the top of one tire would be tipped inboard ~3/8" more than the other (i.e., you're not trying to measure thousandths). Might give you a clue about which parameter to attack...

PS What size rear wheels/tires?

 

Greg, here's why I asked. My DD is a Honda S2000. I run about 3 deg neg camber in the rear. On my first two sets of rear tires, I got less than 10,000 miles before they were toast. Finally, on the third set, I was determined to make them last longer. After asking around, I found that rear toe was likely what was wearing them, not camber. Sure enough, in the US, Honda set about a deg or so rear toe in to keep the car from oversteering. I set the rear toe to zero, left the camber at neg 3, and my last set of rear tires has over 20,000 miles and still looks good.

Interestingly, the rest of the world got rear toe setting different from US on Honda S2000s. Something about the fear of US lawsuits. keeping the rear end in line was more important than performance or tire wear.

Sure, rear toe by itself with 0 camber would wear the whole tire. Rear toe combined with camber wears the inside worse. But, it's the toe that's rubbing the tire off, not the camber. Make sense? It really doesn't make all that much sense to me logically, but I can't argue with my own non-scientific testing on my own car and tires.

 

I am constantly amazed at your ability to come up with a drawing or picture to illustrate your words... being a visual person, I'm also grateful!!

Rick

 

If the rear toe were wrong on one side, when the car drives down the road it will automatically even out, ie crab, effectively sharing the misalignment between the rear wheels.

were the overall toe excessive, wear would be showing on both tires.

Do Steve's quick check from side to side on pretty level ground for camber difference.

 

Not toe OUT. tires should be toe in.

Rear end will become very squirrely with toe out.

 

Guys, thank you all so much. I'm gonna try Steve's camber check method tomorrow...

Greg

PS--my tires are 17", 215 front, 235 rear....

 

Since you have a '77, my first thought was "if he's got the narrow stock 14" tires, it must be way, way out to see such a noticeable difference" -- so sort of relieved that you have the 235s.

I did find that with 225 rears, the camber setting that gave the most even tire wear (street use) was in the -0.5 ~ -0.75 deg range -- i.e., if you use the 308QV spec of ~-1.3 deg, the inboard edges will wear prematurely (esp. with the even wider 235s, but since you're seeing a difference side-to-side you must have something else going on too).