In a message dated 12/17/2001 12:25:36 PM Eastern Standard Time, jschaer@columbus.rr.com writes:
> I assume you are talking about the brake center bolt hole? If it appears to
> be off-center by visually comparing to the wheel/tire, there could be
> several problems. It is very doubtful that the hole is off center in the
> bridge, or relative to the seat stays at the bridge.
>
> 1) The rear wheel dish could be incorrect; IF the frame was completely
> correct, then that would also be evident at the chain stays. BUT, it the
> wheel is centered at the chain stays, that is not a guarantee that the wheel
> is correct. I've seen many mechanics tweek wheels so they seem to sit
> centered in a frame.
>
> 2) The rear drops may not be symmetrical to the plane of the frame; again,
> just because the wheel may appear to be centered at the chain stays, or
> straight compared to the front wheel, doesn't mean the frame is correct. The
> type of check you performed probably wouldn't reveal small frame errors that
> could easily account for what you see.
>
> 3) The rear drops could be positioned incorrectly; the seat stay length, or
> inaccurate jigging and brazing/welding, could easily cause "wheel lean" at
> the brake bridge.
>
> It takes someone with competent alignment techniques and experience to find
> small errors, so it depends on how "right" you want the frame to be vs. the
> potential cost to get it there. Vertical alignment error in the rear wheel
> is not very noticible compared to horizontal alignment error, but it depends
> on how picky you are and how you ride.
>
> T check yourself, I would advise start with a verifiable "golden wheel" that
> you know to be dished correctly within 0.5mm or so. Then check that the rear
> drops are parallel. Be sure to install the wheel on the ground with some
> slight load on the bike before closing the skewer (skewer must not be bent
> at all), to ensure the axle is completely seated in the arch of the dropout.
> Observe the position at both the chain stays and brake bolt. My guess is
> that you'll still find lateral displacement at the brake bolt, and that
> effectively the chain stay length is off. The simplest way to fix is to file
> the dropout arch a little. You'd be shocked at the number of very high-end
> frame makers use this technique to "align" their frames. Since the modern
> aluminum frames are not very alignable by standard techniques, subtle arrors
> are taken out by filing. Often you can even see the file marks still in the
> droppout arch. They usually don't even re-finish the surface, and it's
> usually painted or clearcoated over.
>
> Just file very conservatively. It doesn't take much material removal at the
> dropout to make a substantial difference at the wheel circumference. You'll
> probably be taking something like 0.005" to 0.010" off. It's hard for me to
> describe in short how to do this or where exactly to file, so if you don't
> see the process easily in your head, you might want to defer to a
> framebuilder or good mechanic. If you have a junk bike, a little
> trial-and-error practice goes a long way.
>
Well..... what if the hole is off center? Not sure why you were so quick to discount that as a possibility.
Pete Geurds
Douglassville, PA