UFO Rotors - $$

[Bernie Benz]

Further comment interlaced below.

> From: "Tom Mullane" <tmullane at snet.net>
> Date: Thu, 1 May 2003 20:14:49 -0400
> To: "'Bernie Benz'" <b.benz at charter.net>
> Cc: "'200q20V mailing list'" <200q20v at audifans.com>
> Subject: RE: UFO Rotors - $$
>
> Bernie,
>
> Question: "it should be uneven and inconsistent, inasmuch as the wheels are
> not turning in sync all the time, so will be in and out of phase"  I think I
> follow you here; because the car does not drive in a perfectly straight line
> all the time, one wheel is prone to make more rotations than the other
> occasionally, resulting in the wheels/rotors being in different points in
> the rotation relative to each other, yes?
Right.

> The pulsation is inconsistent.
> It depends mainly on the speed at which the brakes are applied (50-55 seems
> really bad) and how hard the pedal is depressed.  Hard braking off an exit
> ramp at 55 generally results in a fairly violent shaking of the steering.
> Light braking at low speed produces a gentle pulsing.  It also seems to get
> worse.  I switch on and off with the Coupe, and every time I get bad in the
> 200, I am unpleasantly surprised.
Braking torque oscillations may well be agravating a loose steering system.
>
> As far as rotor wear, I would think that running rotors below spec would
> result in increased fade, as less massive rotors heat up faster (though I
> s'pose they cool faster, too).  I thought that was why folks were hesitant
> to go to the G60's?
I would guess that the difference in total mass of new vs min spec rotors is
<2 or 3%.  Have you ever experienced fade in your driving style?  Not me.
My driving style is to avoid it.  The main reason to stick with UFOs is
their 15% advantage in potential braking torque over G60s, without
consideration of any thermal mass advantage.
>
> How about turning the UFO's?  Anyone had any success here?
Yes, over the years several on this list have expressed great success with
one or two machine shops that have developed the tooling to machine UFOs.
Maybe it was real, but never documented with before and after runout
measurements.  But I have absolutely no faith in the average brake shop's
brake lathe to accurately machine conventional rotors.  I have measured with
dial indicator the runout of these lathe hubs.  0.005 to 0.010" runout at
the hub, which translates 3X at the rotor OD.  Ask first when the lathe was
last calibrated, and to see the corrected results.  The response is always:
Huh???

I have silky smooth brakes on both the UFOs and G60s, I believe primarily
due to the caliper and caliper slide condition, and biannual fluid changes.
Overhaul them!

Bernie
>
> Thanks.
>
> Tom