Brake Sizing
[ August 28th, 2008 ] By: Mark Ozimek Posted in » Ramblings
Tonight I’ll cover something a bit different: The size of brakes needed on different surfaces. There are various sorts of surfaces one can trek in a rally event, from pavement to ice and snow, and they all have different traction requirements.
You may be thinking “Well, why does this matter, if brakes can work on pavement, why not on snow?”
The answer lies in the responsiveness and feel of the brakes. A major determining factor in how much stopping power brakes provide is the swept area the disc. The easiest way to change this is to change the diameter of the discs.Pretty obviously, the bigger they are, the more area there is.
With more area, more torque is produced with the same amount of pressure on the pads, making the brakes feel much more responsive. While this is usually a good thing, being too responsive is not, and will end up being very tiring to drive.
So one option to make driving in low traction conditions, like gravel and ice, easier is to reduce the braking power by putting on smaller rotors and caliper hangers to move the pads in a corresponding distance. Since many cars and setups are very different, it’s hard to give actual numbers on how much to reduce the amount of braking power available. In addition, it is something that you need to experience and decide for yourself based on your own tastes in how your car feels. I know that personally, I like it when I need to brake like I mean it, and get very disconcerted when I drive a car with a very light feeling brake pedal. As a result, I’m sure the choices I would make in brake setup are different than those Charles would make.
An alternate idea, and possibly easier, is make an adjustable vacuum assist mechanism for the brake booster, although this will mean additional weight on both the chassis and wheels, as it allows you to run with the big brakes all the time.
August 29th, 2008 at 8:54 pm
Excellent points! I see people getting the biggest brakes they can afford for their cars all the time.
People buy brake setups used on supercars when, no offense intended, their cars have 1/2 the torque, HP, and dynamic suspension of the cars whose setups they are emulating.
Along similar lines, cryo rotors, ceramic pads, race pad compounds, and other exotic brake setups often require very demanding environments just to perform “normally,” and will be very harsh, if not, actually less effective, in street or even occasional autocross usage.
I hope we get to talk about clutches soon! :-)
September 1st, 2008 at 9:21 pm
Heh, an excellent point on the racing pads. It takes a lot of effort to keep them up to temperature on the street, and you will invariably break several laws in the process!
Although clutches… mmm, yummy. Definitely a good thought.