There is quite a bit to it. It has to do with overall weight, weight distribution, and placement of the weight. Also the type and capability of the suspension front and rear. As mentioned before, Walker Evans had a truck or two with extremely short WB and they were pretty damn fast. I think it was Bunderson who built some cars at least 130" and they worked well too. What is right for one is not necessarily right for another. You might consider this as a practical limit just like motorcycles and road race vehicles. The limit is brought about by several factors such as vehicle width and weight, power limits, wheel size and weight, fuel consumption, drivetrain limits, etc. There is the constant battle of sprung vs. unsprung weight. All of these must be considered. Longer WB would handle the bumps better but would turn like du-du, and weigh more. Then you start down the road of more power, stronger drive trains, all wheel drive, etc, etc, and reliability becomes an issue (sound familiar?). Practical size limits have been achieved in all forms of racing. This is not just because of the rules either. There is a level of efficiency that is reached. A much larger vehicle would require a tremendous amount of money AND proper designing. A bigger heavier beast generally does not like to fly, turn in the rough, or accelerate quickly, but it must to win any races.
<font color=orange>The best ideas are the ones that look obvious to the casual observer.</font color=orange>
