Drum brakes are ideal for the rear axle because they are cheaper and take less hydraulic force to activate. Overall vehicle design determines front versus rear brake bias, but most rear brakes should never provide more than 40% of the stopping power at any given time. As such, they don't develop nearly as much heat as the front brakes. If they weren't designed for this lesser load, the rear brakes would lock up every time you stepped on the brake pedal, or at least the anti-locking braking system(ABS) would be activating all the time. Providing just the right amount of braking power and vehicle stability requires the following: 1) smaller brake calipers give less clamping force. 2) smaller brake pad surface and less aggressive brake pad material for decreased friction. 3)smaller diameter brake rotors for less stopping torque 4)thinner brake rotors are lighter and don't have to endure that much heat. 5)solid brake rotors don't have to dissipate that much heat. 6)drum brakes, on many economy cars, with all the above benefits.