View Single Post
      02-22-2007, 11:56 AM   #53
Major General
ksfrogman's Avatar

Drives: E90 330i 6MT
Join Date: Nov 2005
Location: Torrance, CA

iTrader: (12)

Garage List
2006 330i  [0.00]
2006 330i  [0.00]
Send a message via AIM to ksfrogman
Originally Posted by RiXst3r View Post
is it just me, or does the BBK have less rotor "surface" area?
old rotor had 2.5 inches of rotor surface, new kit has 2.25 inches...

does that matter?
You're up too early. Go back to sleep!

I am no engineer, but as you know, surface area is two-dimensional, i.e., Area = height x length. The stock rotor actually has a surface that is approx. 2.25 inches high. I took my yardstick back out to the garage (sorry I don't have calipers with me). However, the outer diameter of the stock rotor is about 1" less than that of the Brembo one. The diameter of the wheel too is directly proportional to surface area since Area of a circle = pi*r^2, isn't it? You can calculate the difference between the larger circle (O.D.1) and smaller circle (O.D.2) and come up with surface area if you're really that curious, but this is a moot point, because frictionally speaking, what also matters is the braking surface and pressure exerted on that surface. The aftermarket brake pad surface seems larger than that of the stock one, which uses only 2 pistons.

Example: Back to the issue of outer diameter. Think of yourself as an ant that is racing around a circular track (i.e., my brake rotor). If you're walking on a brake rotor that has an outer diameter of 14" vs one that is 13", your track times would be much longer on that 14" rotor.

One last thought: I would think that the larger the rotor diameter, the more the rotational inertia. In dealing with unsprung weight, I would imagine it best to try minimizing that as you push the rotors outward in design. Tonya Harding spins in ice circles more quickly when her arms are closer to her body (with or without a crowbar in her hand).

Last edited by ksfrogman; 02-22-2007 at 12:16 PM.