What causes tire scrubbing/scallop effect?

[deskjockey]

I changed the rear axle bearings on my 8.25" rear and decided to rotate the tires while I was at it. I noticed that the rear tires were scalloped. I could feel it while rubbing my hand over the center tread while the tire was rolling down the driveway. The lugs on both sides of the tires are cupping too. They're Cooper ST's ran at about 30 psi front and rear. What would cause the tires to scallop the way they did????

[mike94xjpa]

Usually alignment. But that would mean your rear axle is "crooked". Good luck

[Saudade]

http://www.partsamerica.com/MaintenanceTireProblem.aspx

[deskjockey]

Hmm, interesting. How can I check if I'm running dog legged? Where's a good spot to measure to under the Jeep? Actually, the more I think about it...I have been running a Rusty's 3" lift and when I installed the 4degree shims the centering pin wasn't sticking down very far. It's quite possible after all these years that my axle shifted every so slightly. I actually noticed the aluminum shims are starting to chunk away. It's as if they're disolving. Who sells good 4 degree steel shims and replacement centering pins that connect the shim to the spring pack?

[NighthawkXJ]

you can check for dog legged by having a friend follow you, if they can only see a tail light on one side, and the whole jeep on the otherside as you are driving streight, then you are dog legged.

[SteveT]

Hmm, interesting. How can I check if I'm running dog legged? Where's a good spot to measure to under the Jeep? Actually, the more I think about it...I have been running a Rusty's 3" lift and when I installed the 4degree shims the centering pin wasn't sticking down very far. It's quite possible after all these years that my axle shifted every so slightly. I actually noticed the aluminum shims are starting to chunk away. It's as if they're disolving. Who sells good 4 degree steel shims and replacement centering pins that connect the shim to the spring pack?

Measure your wheelbase on both sides of the vehicle. Find a common point, like the center cap of the front wheel, and get that distance to the center point of the rear wheel. It should be the same for both sides.

[deskjockey]

I had my son help me measure this evening. I'm out by about 1 - 3/4".