it isn't a different question. it's about where you position the physical matter that was already on the kart.

 

Adding downforce is TOTALLY different from adding weight!

With downforce, you increase normal force while adding negligible mass. 100 lb. of rear downforce, with little to no additional mass at the rear will reduce oversteer/increase understeer. You've added lateral grip without adding very much at all to the mass that has to be laterally accelerated.

Adding 100 lb. of MASS at the rear is fundamentally different. You won't get enough additional rear grip (again because of the nonlinear nature of tire grip vs. normal force) to compensate for the additional mass. More oversteer.

 

yea i know

 

It is a somewhat different question. If you are dynamically moving your mass within the cart, it is a dynamic situation. The instant you begin to push your own mass rearward, you temporarily load the front and unload the rear. When you stop accelerating your mass rearward, you load the rears and unload the fronts. The final steady state situation is that you have put more weight on the rear wheels of the cart, but what has happened during the entire process is that more weight initially went slightly to the fronts, then to the rear.

The original question was regarding the oversteer/understeer behavior of a car with more static rear weight bias.