comp TA

Bernie Benz b.m.benz at
Tue Sep 17 08:14:11 EDT 2002

Further comment interlaced below.  Bernie

> From: Scalmanini Steve <sscalmanini at>
> Date: Tue, 17 Sep 2002 00:11:14 -0700 (PDT)
> To: 200q20v at
> Cc: Bernie Benz <b.m.benz at>
> Subject: Re: comp TA
> Very personally perceived experience.  Several times
> between '95 & '00 after several months of
> vibration-free driving after a rebalance and mounting
> freshly-turned UFOs, I felt the slightest steering
> wheel vibration begin at some speed between 50-60 mph
> (during driving at first, not braking).
If a wheel imbalance condition exists and is most evident at a given speed
(a resonant condition with the suspension) it exists with or without
braking, maybe with a change in perception when combined with rotor runout
and guide pin problems.
> After a rebalance, the vibration remained during braking due
> to you-know-what.
IMO, inertial imbalance and rotor runout are two different and unrelated
> After several of these events I figured the tire
> imbalance was transferring enough vibration to the
> rotors to warp them just enough to get them started,
> until they eventually reached their common .005-.007
> TIR out of true.  After mounting freshly turned
> rotors, both problems were gone for maybe 6-9 months
> (5K-10K miles).
You measured this gross runout! .005-.007?  What were they when freshly
turned?  If <.001, the turning process evidently introduced stresses into
the UFO carrier web that were relieved over time.  Experiment:  Quantify the
runout of one of your freshly turned extra rotors, stress relieve it and
remeasure.  Not quite a high enough temp, but you could get some idea of the
problem by putting the rotor in your kitchen oven at 500F over night.
> I dealt with the problem by buying three extra sets of
> UFOs and getting all the extras turned at that machine
> shop in San Jose (I'm the guy that found that shop).
> However, I haven't had to change rotors since I
> switched to Michelin Pilot Sports a year or so ago.
Indicates a tire problem with the Comp TAs, doesn't it?

> Now those extra UFOs are catching dust in storage (but
> not available for sale yet).
Turned rotors could be a hard sell, at least to me.
> I might have gotten the idea from a post back in the
> mid 90s (maybe on the main list) of someone who warped
> their rotors driving home after skiing, I think it
> was.  Enough snow had accumulated on the bottom of the
> inside of a wheel during the day to throw the wheel
> out of balance (like a temporary wheel weight made of
> ice) and the resulting vibration warped their
> rotor(s?).  Same transfer mechanism, I assume.
> ' any thoughts to add.  I know you're a fan of UFOs,
> and so am I, frankly; I don't intend to convert.
Yes I am, but I'm not a fan of rotor turning, conventional nor UFOs.

> But I've had enough of Comp TAs.  They were great in all
> other respects, however; lasted me 70K on each of two
> sets!  I know some others on the list have had no
> problems with theirs so take that for what it's worth.
> I'll report on the Pilot/UFO compatibility again next
> year; I won't swear the problem is gone until I put
> more miles on the Pilots. Meanwhile, they seem better
> than the TAs in cornering, as they should be at twice
> the price of TA VRs; those HRs must be reeeeally
> inexpensive.
> Steve
> Ukiah, CA

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