I think the rear drive axle tires wearing has something to do with the suspension. In the 60's until the mid 70's I ran Hendrickson walking beams and all 8 tires wore evenly. In the mid 70's is when I started phasing in 4 spring suspension and the rear wear first appeared. In the mid 80's when I started phasing in air ride, it became very apparent. I now try to rotate the drivers at 50k miles. It may also be due to the fact that on my tractors that pull bulk trailers, I center the 5th wheel on the forward axle to get my 12k on the steering axle. 40 years ago we didn't worry about axle weights. It could be that the forward axle gets more traction and the rear one slips a little.
