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RE: floating(?) brake rotor

Peter LaPine asks re floating braking rotors:

>  does this term refer to the 'sliding caliper' design found
>  on the M5?  also previously seen on a mid-80s 535i?
>  with this rotor, there's 1 piston that pushes the pad on that
>  side while drawing the opposing pad/caliper half toward it.

NO.

Sliding calipers are as you describe, and floating rotors are something
else entirely.  Basically, floating rotors are multi-piece, and are not
rigidly affixed to their aluminum "hats", but rather are free to move (a
little bit) on machined pins or now (via Tilton, I've heard) in a dog-drive
arrangement, so as not to build up stress in the whole assembly as the
rotor heats up and cools down.  The construction of these rotors attempts
to keep the weight down (aluminum hat instead of everything made of cast
iron or steel), and retain the heat in the rotor, instead of it
transferring up through the hat into the hub, bearings, etc. By going to
multi-piece construction, the design of the rotor (now simply a flat disc)
and the hat can be optimized around the properties of their respective
materials.

Sliding (sometimes called floating) calipers have one overwhelming
advantage -- they're cheap to make.  I would also guess they're usually
lighter than a fixed-piston design.  Racers overwhelmingly prefer
fixed-caliper designs, like the E12 530i & 528i (and the M1, by the way,
which uses 528i front calipers (w/spacers) in the front and 320i front
calipers (w/spacers? -- I forgot) in the rear) have. All Porsche 911s, for
instance, used fixed-caliper, 2-or 4-pot units. Indy and F1 cars often use
6-pot fixed calipers (aluminum body, stainless or titanium pistons), with
the pistons ("pots") of differing sizes. 

Come to think of it, the E36 M3 is the only European high-performance car I
know of that currently uses "sliders".  American manufacturers (notably
Ford, see the new Mustang (incl. the Cobra) and the '97 F-150, both with
twin-pot sliders) love sliders. Harry Noble has informed me that the M3
(the 3.2L '97 model) now uses multi-piece floating rotors, too, with 24
pins holding the rotor to the hat. I think the 850CSi (an ///M product,
Euro-only) replaces the stock sliders with 4-pot units.

>  BMW used an ATE caliper on the 1975 R90S motorcycle that
>  allowed the caliper to pivot L/R ('hinged' at the rear) -
>  I thought *that* was considered a 'floating' caliper...
I SAW THOSE! They were unique, to put it mildly. The pads are chamfered in
a weird way, too. I'd tend to call that a "pivoting" caliper. 

What will those cwazy Germans think of next ... Hasenpfeffer -- for cats?
"Katzen wuerden Whiskas kaufen" (the Whiskas slogan in Germany and
Switzerland) translates DIRECTLY to "Kats would buy Whiskas" -- how's that
for some exciting advertising? Probably from the same agency as the Menthos
ads.

 ___________________________________________
| Andrew E. Kalman, Ph.D.   aek@domain.elided  |
|        standard disclaimers apply         | 
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