My basic automotive engineering analysis of putting weight directly over the rear wheels (assuming no change in CG, not a perfect analysis):
Edit: Just realized how long that is.. so TL;DR - your maximum traction won't change and the car will oversteer more than previous.
Where µ is the coefficient of friction (irrelevant if we’re comparing identical cars with the exception of added weight in the rear), a is the longitudinal distance from the center of gravity (CG) to the front axle, b is the longitudinal distance from the CG to the rear axle, m is the mass of the car, g is the acceleration due to gravity, h is the vertical distance from the ground to the CG, l is the distance from the front axle to the rear, Rr is the rolling resistance of the tires. In our discussion, the only difference will be the weight distribution as well as the overall mass of the car.
Acceleration:
http://cars.about.com/od/scion/fr/20...r-S-Review.htm 53% front (a/l = 0.53), 47% rear (b/l = 0.47) weight distribution, m*g (stock) = 2800 lbs, m*g (added) = 2950 lbs, I’ll assume the CG remains at the same height although that’s probably not entirely true it shouldn’t be affected too much. The equation gets much simpler, as shown. Stock: Wf = 2800*0.53 = 1484, Wr = 2800*0.47 = 1316. New: Wf = 1484, Wr = 1466 (not perfect, I know, but close enough for argument’s sake) > a/l = 50.3%, b/l = 49.7%. So the weight in the front hasn’t changed (a/l) so your maximum tractive effort (maximum acceleration) hasn’t changed.
Steering: The equation that matters is the understeer gradient. The cornering stiffness will not change, nor will the weight in the front. More weight in the rear will cause this gradient to become more negative, meaning the car will oversteer more.
Note: This is not perfect and the assumptions for maximum tractive effort can be disputed; however, the math for the understeer gradient is simple and a car with more weight in the rear than previous will oversteer more heavily than previous.