why aren't the frame rails of TT set evenly from the sides?

Lynnmor wrote:
Are the wheels equidistant from the sides? Are the springs mounted to the frame rails and are they equidistant there?

This is probably the most critical point and assuming the springs sit under the main beams, the wheels on one side would sit 4" further in from the side than the other...or one side would have a much longer cantilever from the springs to wheels.

It should be pretty easy to check out as the frame is usually visible where the axles connect.