Originally Posted by ResIpsa

There is a really good reason why our cars (and every other car on the planet) has smaller rear brakes. This is because too much rear brake will cause the rears to lock up under heavy braking and spin your car.

Even on cars that appear to have identical size front and rear calipers, if you actually took the caliper off you would notice that the pistons in the rear are one third of the size of the fronts.