besides that, you wouldnt want 13" brakes at all four corners. you would most likely go into a tail spin every time you hit the brakes. Front brakes must be larger to get optimal braking, they do most of the work. You can go bigger in the rear just not the same size as the fronts.
If you have ABS the rears should not lock. A friend of mine placed very large oversized breaks on rear of his card with no ill effects. It did stop faster but not as much as doing the fronts.
