I meant to ask about that. There's a side note in their instructions saying they recommend that for " a better feel".
I got antsy and went out with a flashlight and a couple of clamps. In the above pic the tires are straight ahead. I can pull it left and right all the way without any binding. In fact the angle at the joint didn't look to move very much.
I will need to make another bracket or weld a piece on the bottom of what I have. Raising it that 1/4 of an inch lifted it off the top of the rail the same amount. I'll do a mock up with a piece of angle iron clamped in place first.
