I would be careful adding weight behind the back axle. Have you ever towed a trailer or seen a trailer with too much tongue weight? It uses the back axle as a fulcrum and takes weight off the front tires. This leaves you in a situation when you do a hard brake, the front tires lock up and slide because they have no weight.
Just my 2 cents, but if I were to add weight, I would place it over, or slightly in front of the rear axle.
Jon
Ah yes, good point Jon, but you can get by with less weight the further away you place the weight behind the axle. Weight all the way back takes advantage of leverage, so you will not need as much weight to apply the same amount of force on the rear axle as you would if the weight was put over the axle.
It is a balancing act, requiring trial and error to get the weight right, so as to not pull the front tires off the ground..
