OK.. I couldn't resist...
MDM, so you are saying that I should translate your experience with a push mower to my 4x4 1800lbs tractor? C'mon? It's not acceptable or socially responsible to give this kinda advice. The laws of physics, propulsion dynamics, weight ratios etcs are so drastically different between the two it is just foolhard to try and say one can compare and then be related to the other (gee, are we talking with weights here, FEL, what is the pitch of the incline, etc.).
Gizmo, you mentioned something about "do the math". Hey, provide the equation and I'll compute it for you. Please be sure to include all relevant attributes and variables. Also, be sure to include density of fill for tires, incline, gravitational pull, balances on a given machine, etc. Lets keep the equation set for use for the original poster, since that alone will suffice as a decent answer.
In the meantime, get your tractors running and have a good and safe time! /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif -Art