Ingenieur

they are floating
and you can't move them by hand
they only move radially
if you heat them up you will see them expand in diameter
and the inner diameter will get smaller
by a very small margin

if you could 'rock' them they would vibrate like a biotch
they can unifiormly expand/slide outward in unison, not eccentrically

MB, Brembo and BMW M call them floating
I'm in good company
the people who MAKE them call them floating

OEM supplier Zimmerman has filled the gap left by BMW when they decided to stop importing the Euro E46 M3 brake rotors to the US. The Euro rotors are cross-drilled and floating, providing much improved cooling over the stock US brakes and are a direct replacement for the stock US rotors. These Zimmerman floating rotors are made in Germany and are almost identical to the Genuine BMW floating rotors that are no longer available to the US. They share similar drill patterns, floating design, offset, and vaning as the OE BMW parts. Zimmerman has been an OE supplier to a large number of German cars, including Porsche and Mercedes.


take a very close look at the pins
they allow it to slide/float inward/outward radially only
they are tight, you can't shake them, yet they will move under the thermal expansion of the disc

m a x i m u s

perhaps these are all "floating" and there are varying degrees of movement depending on design?

I'm also curious about natman's giro disc two-piece rotors (different thread) that are making noise ... maybe the rattle is from movement like in the moto video above?

zibby43

Thank you! That makes sense. Appreciate the information.

whoover

Exactly. Every two-piece rotor has to deal with the different coefficients of expansion. The Brembo dual-cast design is more advanced than the sliding-pin design, but they both do the same thing: keep the assembly from warping and worse when the aluminum expands more than the iron.

But the references to "true floating rotor" vs. the marketing-speak of calling a fixed-rotor design that deals with differential expansion comes from the motorcycle and racecar crowds that know that actual floating rotors allow significant movement of the disk with respect to the hub as well as allowing for differential expansion.

This allows the rotor to self-center within the caliper to deal with small imbalances in caliper piston travel. That's why racers speak of (true) floating calipers reducing brake judder at high speed.

Here's another thread where purists object to people buying the marketing hype by calling fixed two-piece rotors "floating."
http://singletrackworld.com/forum/to...ng-disc-rotors

Ingenieur

Yes
They are all floating of various design approaches
The rotor disc 'floats' in relation to the hub to allow movement
This minimzes warping/distortion due to thermal expansion

Ingenieur

The AMG are 'true' floating
So are the RS4 and M3
They are 2 pieces affixed ( not fixed) by a pinned joint
Pinned as in the structural sense, ie some freedom of movement, but not necessarily a round 'pin'

Having said that the word 'true' is superfilous since it ia a floating rotor in actuality and therefore 'true' by default

What the hell is a purist? Lol
Somehow more enlightened or regal
Gobblty gook
Just a bunch of hooey by non engineers over contemplating nonsense
Oh chad I have real floating rotors where as youhave s
Pseudo ones
Lol

The engineers that build them call them floating without qualification

whoover

I can just see it. Going up to the guy with the racing bike in the youtube I linked and saying, "those two are exactly the same and I know because I'm an engineer." I saw lots of that in my day. The only cure is getting such engineers to spend more time with customers. Even that doesn't always work.

Ingenieur

The engineers who MAKE them call them floating
The car mfgs who use them call them floating

Not
'True'
Not
'Full'
But
Floating

As in the X Y axis vs X Y Z

One is a motorcycle
One is an automobile
The requirements and dynamics are very different

We call them 'clients' not customers
We want a relationship with them not only a transaction
I regularly reminded my employees that the Client singed their paycheck
I was only representing them
When they complained about phone calls and issues I reminded them that that is good
When they stop calling with their issues that is bad

whoover

Hopefully the clients signed the paychecks before they singed them. Sorry, couldn't resist but we all make typos.

Actually, lots of the threads I posted talked about freely floating rotors on cars, not just bikes. And the benefits (like reduced judder) versus the drawbacks (like noise of rotors moving around). Anyway, no point in posting more.