My boss and I were arguing about why a lot of cars have bigger front brakes than rears. I said it's to save weight, help accleration and because the front end has more momentum with brake dive. He thinks it's just to save money for the car companies.

Does anyone know the official reason?

 

Its because the fronts do 70-80% of the braking on most cars and if they were as small as most rears you would over heat themnever get stopped. Transvers due to their minimalload, there is no reason for the rears to beso large. If you notice most rear brakes arent vented and all fronts are. Its simply due to the specific load of braking to which they are subjected. As far as I know it has nothing to do with saving money or acceleration gains.

 

Correct. The fronts are bigger because they do a majority of the braking. The reason they do a majority of the braking is that during deceleration/braking, the weight/momentum of the vehicle shifts towards the front end increasing the loads the front must deal with.

If you had the same size brakes front/rear, you would either have

1)A bad brake fade issue (poor braking performance due to undersized front rotor) or
2) Rear brakes that are way more than they need to be which increases weight and the cost to the consumer. (Why put a 14" rotor/6-piston caliper on the rear if a 12" 4-piston does the job just as well.)