I see you three wheelers run a much shorter wheel base, but on a "4 wheels must touch" (and be flat) car, do you want to extend as far as possible? I am assuming moving the fronts back would give me more speed on the slope, but less stability? Wood track if that factors in at all. I ran 5.60" last year and did well, but could extend a little further (5.75") or shorten?
