Odd Tire Wear on beam axle left spring car

So I have this odd tire wear on the back of my Datsun 1200 that I race. The very inside edge of the rear tires get scalloped out. This is not like a car with to much camber, the tread is scooped away with the rubber feather out on the side wall (like it stuck in a mold). The feather makes me doubt the axle tube is bent. My other thought is the axle is moving around on the leaf spring centering pins. Any theories welcome

I've included a link to the photo as I'm not tech savvy

pic

http://datsun1200.com/modules/myalbum/photo.php?lid=26869&cid=18

Both tires do that to the inside edge? Thats strange. Have you had the car aligned? I would love to know what it shows for rear camber and toe. Besides the axle being bent i really dont know what to think, unless that could come from spending a lot of time sliding through corners with the rear loose. That would lift the inside wheel, and the outside would be scrubbing the tread toward the inner shoulder. Im just guessing here, i have literally zero experience dealing with road course race cars.

Ever see what the tread of a tire does in a corner ? It lifts the inside edge. I say probably normal wear.

That kind of wear looks far from normal to me! +1 for checking rear camber and toe.

What's interesting is that the wear across the rest of the tread is pretty even. It's worth checking rear toe but I'm not really sure you've got a problem What does the tire look like about half way through its life? That'll tell you more than what it looks like when it's down that far.

Is your axle moving fore/aft during hard cornering? Or crossing itself up as in moving one side forward and the other aft? Do you have a panhard/watts axle location system?

Fueled by Caffeine wrote: Or crossing itself up as in moving one side forward and the other aft?

It shouldn't much be with leaf springs. Although if it is, I'd say it's roll-steering in the wrong direction. If it were doing it in the helpful direction (outside wheel goes back / inside wheel goes forward) it would actually reduce tire wear a little.

You need a right spring, too.

What kind of limited slip are you running? I've seen late models with locked rears do that to the outside rear on tight ovals. Since both of your tires are outsides at some point it makes sense you're seeing it on both. I would start by adding a couple pounds of air to the rear tires. Sometimes you live with it because that's where the car is fastest but if you can bump up the pressures without losing time your tires may thank you. By chance do you have tire temps from the run that did that?

iceracer wrote: Ever see what the tread of a tire does in a corner ? It lifts the inside edge. I say probably normal wear.

I don't think I'm picking up what you're putting down... Picking up that inner edge would suggest to me that it would be less worn than the center/outside, not specifically scooped out.

I suspect I'm misunderstanding?

Taking the "all theories welcome" and running with it, I have this utterly insane theory: The feather is generated during normal wear (outside tire, heavily loaded), and the scoop is generated when the almost-completely-unweighted inside tire is spun on exit. Yes, I know we're talking about a Datsun 1200, but unweight it enough...

Hey, I said it was insane...

In reply to Ransom:

I think the wear he's got is more a combination of the tire sliding plus somewhat chattering on the pavement as the sidewall deforms. I think it's carrying more weight on the inside edge and adding some air will spread the load across the tread. It's hard to tell from a pic on my phone though.

In reply to Wall-e:

Still seems weird without annihilating the outside shoulder, but it absolutely sounds less crazy than my theory.

The diff is Nissan Competition clutch style, it occurs to me that it may be tight

We've considered going up a pound on the air pressure.

Ransom I've got the big block 1508cc motor in it belting out 105whp........does a mind blowing 111mph at the fastest part of the track.

A test with a pyrometer will tell a lot.

In reply to Ransom:

I heard an explanation years ago that had to do with the sidewalls on a bias slick deforming and the inside of the tire wrinkling making it wear more oddly than the outer edge which maintained a more constant contact with the track. I should have asked but assumed the tires were bias ply Hoosiers which I believe are similar in construction to the slicks we ran.

kind of normal. My Dwarfs would do that. You can check toe and caster relatively easy to do pull the wheels and brakes off clamp straight edges (Levels are nice and flat) and two tape measures (get new ones so there same lot and clean etc.) When I build rear housings I shoot for less than 1/8th over 4 ft, at tire diameters that alot less. rear housing move easly with a torch and ice water. Heat the High spot a nice cherry red dot the size of a quarter then hit it with ice water then soak a rag and let it cool and recheck. Also be sure to check the axle flanges are not bent! If its badly bent you realy want to put it in a jig that goes off the diff carrier bearing bores cause thats what maters as axle turns around that.