Much has been discussed on these threads re: the brake dust that builds up on the front wheels. My question is the following: why does the vehicle use more front than rear brake? I am sure the answer is simple but I would love to know. Thanks !

 

Just simple law of physics, there is a weight transfer to the front whenever you apply the brake. The harder you step on the brake, the more is the weight transfer taking place.

On a side note, I've remembered Mario Andretti saying that if someone told him that the use of the brake is solely for stopping the car, then whoever said that can't be a good racer. Obviously, a good racer should know the intricacies of using the brake to balance the car as well as effecting a weight transfer to help him to gain that hundres of a second advantage over his competitors.

 

during deceleration, you need a lot of grip to continue to decelerate, and maintain grip on the road with your front wheels. to do this, the front wheels are enlisted to do most of the work braking, as doing so will shift the balance of the car (and thus the amount of weight) from the back to the front with the momentum of the car continuing forward. this will give you more grip on the front (more force down equals more force up on the tyres), for both harder braking and steering. it does lift some grip off of the rear wheels, though, but when stopping in a mostly straight line (and considering most passenger cars are heavier in the back than the front when loaded) it's a good comprimise.

also, from a performance standpoint, you can think of each wheel of having 100% of their grip (optimally). the rear wheels would be doing the accelerating and stabilizing (lots of cornering demand on the rears), while the fronts would do the braking and pointing... it makes sense from that perspective as well (spreading the work the tyres to around more evenly).

 

The same is true on all wheeled vehicles. 75-80% of stopping power is in the front. That's why front rotors are larger than rears. Between these two other replies they've got your answer covered. Good explenation guys.

 

This is especially apparant if you ride motocross bikes.
I would guess that 90% of your braking power is in the front brake. When you grab it, lots of weight shifts forward and the front forks compress a lot. The rear brakes add little to the stopping , but are useful to slide the rear end around in a turn.

It is even a recomended rideing technique to drag the front brake in a rutted turn, this keeps weight shifted on the front end to keep you from falling out of the rut.