Originally Posted by Matt Trimmings

Actually Jesse, its the position of the front caster block. You shim it differently to maintain wheelbase. AE shouldnt have said "rear casterblock" It should have just said casterblock.

Originally Posted by Dan Hamann

The rear shim on the [front] caster block. Not the rear of the car. To maintain overall wheelbase, you adjust the caster block spacing to counter the movement of the axle with the different trailing positions. The "Rear Caster Block Wheelbase Shim."