Re: <ALL> Floating Rotors

[Neil Maller <neilmaller@xxxxxxxxxxxxxxxx>]

>Date: Thu, 13 Aug 1998 13:55:39 -0400
>From: "Crews, Shawn B" <Shawn.Crews@domain.elided>
>Subject: <ALL> Floating Rotors
>
> Other than the following decription , what can you tell me about how
> floating rotors work?  What part is "floating?"  Are there any
> disadvantages to them?  Are they for street use as well as track use?
> How does the life cycle compare with OEM rotors, aside from the
> warpage issue?

The M3 front rotors are less than optimally designed for heat resistance 
in at least two ways. First the air intake in the eye is on one face of 
the rotor only. The other face forms a continuous web to the rotor hat. 
Both mechanically and thermally the rotor is therefore quite asymmetric. 
As it heats it will tend to dish, and on cooling may or may not return to 
its original shape. Secondly it's not a full-floating design. When the 
outer portion gets severely heated it expands more, but closer to the 
centre the rotor naturally runs cooler and expands less. The differential 
expansion from this temperature gradient will also tend to dish the rotor.

The term "full floating" refers to the ability of the rotor to expand 
independently from its hub, since the rotor floats on its mount to the 
hub.

The 2-piece Euro rotor (also known as the BMW Motorsport rotor) from the 
M3 Lightweight uses a full-flaoting design. The rotor has a ringlike 
configuration, with 12 steel spokes pointing inward. On to these spokes 
is cast an aluminum hub, leaving an annular gap between the hub and the 
inner diameter of the rotor. The rotor is now mechanically and thermally 
symmetrical, as well as being free to expand radially on the steel spoke 
pins. As added benefits, air can now enter from both sides of the rotor, 
and the aluminum hat saves unsprung weight.

The M-Sport rotors are certainly more warp resistant, although they 
aren't totally warp proof.

Neil
96 M3, M-Sport rotors

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