I need to know it for a science project, and I know about friction and that basic stuff, but I need information from a live person. I am going to test this project by putting different weights on a remote control car. I just need a bunch of facts and background knowledge from an expert.

Well, do you know the formula for the force of friction a body experiences when it moves?

It's given by the formula:

F = \mu R

Where mu is a constant for the particular type of contact between the car and the surface it's running on,
R is the normal reaction of the car and is equal to the total weight of that car.