|
Bigger Brakes Part 1
Why install bigger brakes on your car, you say. Isn't it enough that I install higher quality brakes, with the same size ?
No it isn't. Higher quality brakes will improve your braking some, with more vents (drilling), slotting and maybe more pistons. But the thing that will really improve braking performance is size. Size as in larger diameter discs and bigger, multi-piston calipers.
There are two main reasons why bigger brakes is the key to getting more stopping power:
Bigger brakes (discs) have more surface area and can therefore get rid of more heat than smaller brakes, and heat is a brakes worst enemy. The heat can do three things: Melt the surface of your brakepads (glazing) which makes them smooth and reduce the friction between pad and rotor. Heat can make your calipers so hot that the brakefluid boils; boiling creates airbubbles and bubbles are compressible, which in turn allows you to press your brakepedal to the floor without any significant effect on your car's speed. And last but not least high temperatures is not good for the brakediscs: Discs will tolerate heat up to a certain temperature, but higher than that they will warp, or even crack if the temperature is high enough. That is unless you have carbon brakediscs like the ones used on F1 cars.
Bigger brakes have more leverage on the tire so less braking force from the brake makes for more stopping power at the tire. The reason for this is showed in these equations:
Heat
One of the two reasons for bigger brakes is heat. The bigger discs will get rid of more heat than smaller discs because of it's increased surface area. It's fair to say that most of the heat will dissipate from the area of the brakedisk that is wented. I.e the surface the brakepad touches and the surface inside the vent channels in the disk. And of course the area of the holes in the disk if it's cross drilled.
If we assume that the standard disc of 278mm and a 340mm disc have the same height where the pad touch the disk (which is 55 mm for the standard disc) then the area dissipating heat will increase by almost 28%. Of course the new bigger disc will probably be drilled, and have a larger area inside of the braking-surface that also helps. All these factors combined will probably increase the amount of heat the disc can dissipate by about 40%.
To discover why the bigger discs are even more than 40% better; read on.
Forces
I calculate this exactly at the time when the wheel has stopped rotating and slides over the concrete. We have, as the wheel is stationary (stationary here means not rotating, but still sliding), that the sum of the torques acting on the wheel is zero (if not, it would rotate). In this equation:
Ms = The torques acting on the wheel calculated from the center of the wheel.
Ft = The force acting on the wheel (actually the tire) from the ground as it slides.
rw = The radius of the wheel inclusive tire.
Fbr = The force acting on the brakedisc from the brakepad in the caliper.
rbr = The radius of the brakedisc.
