Scrub radius??

[ezcurra]

Hello,

While debating what axle width/hub/backspacing to use in my M715's dana 60, I noticed this in my other Jeep, which has a Dodge D60 with stock rims and tires. I imagined that the axis from the kingpin should intersect the center of the tire's contact patch, but it is not even in the contact area! I would think this would make turning more problematic and would accelerate tire wear. Why is it like that??

Thanks,

Mikel



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[AKAMAC]

The KPA is in direct correlation to the axle angle. What changes is the camber when the radius moves. The move to upper/lower control arms from straight axle king pin systems was the geometry that went from a 1:2 ratio to a 2:5 ratio.

A look at the VW Bug front suspension changes in the late 60s will provide some neat stuff on the king pin/ ball joint/ strut suspension systems. Remember the Twin-I-Beam Ford mess that lasted 20+ years.

 

[BTowler]

You are correct, it should intersect at the center of the tread ideally. When the tire is completely outside the scrub radius as in the picture the tire is being pushed back and forth when turning instead of pivoting on an axis, which leads to increased tire wear.