From: jobst.brandt@stanfordalumni.org
Subject: Re: Wheel truing with dial indicators
Newsgroups: rec.bicycles.tech
Message-ID: <a8%3a.66701$Ik.2837426@typhoon.sonic.net>
Date: Mon, 17 Feb 2003 06:17:42 GMT

anonymous writes timidly:

> I just put together a truing stand with dial indicators for radial
> and lateral truing.  Also, a dish tool with a dial indicator.  (No
> flames on this, please - I know that some will say that this level
> of precision is overkill but I like making things.)

> While Jobst's fine book suggests that dial indicators have some
> value, I haven't found any reference that tells me what level of
> truing and dish accuracy is considered acceptable.  I don't have
> enough experience to know by look/feel/calipers when a wheel is
> considered good enough so I can't translate build quality by those
> more subjective standards into objective measurement criteria.  What
> are reasonable targets in thousandths?

Depending on what sort of brakes and pad clearance you use, lateral
alignment between +-0.005 is fine.  Just remember that brake pads drag
on rear wheels anyway with dual pivot brakes because their higher
mechanical advantage demands lower brake pad clearance.  For this
reason many professional riders leave the rear QR open on long climbs
and Campagnolo switched back to a single pivot 1:1 ratio caliper for
rear brakes.

These are the criteria for trueness, aside from the need for uniform
tension among spokes of the same side for rear wheels and all spokes
for front wheels.  It seems to me that if you are designing tools, the
goal should already be known and the method of achieving that arrived
upon from practice.  Quantifying lateral and vertical trueness is one
thing, but doing it so that it assists truing a wheel requires more
than just that.  It must be practical.  Reading numbers may not be as
useful to the experienced mechanic than watching an air gap between
rim and gauge point grow and shrink when the wheel is rotated.  This
method has served well with good results for a long time.

Jobst Brandt
jobst.brandt@stanfordalumni.org
Palo Alto CA

From: jobst.brandt@stanfordalumni.org
Subject: Re: Wheel truing with dial indicators
Newsgroups: rec.bicycles.tech
Message-ID: <Y204a.66710$Ik.2838774@typhoon.sonic.net>
Date: Mon, 17 Feb 2003 07:20:24 GMT

Shane Stanley writes:

>> Depending on what sort of brakes and pad clearance you use, lateral
>> alignment between +-0.005 is fine.

> What units are you using there?

Oh how clever.  What else?  Did you perhaps think millimeters,
nanometers, or Angstroms.  This reminds me of Snap-on Tools changing
their metric wrench markings to, for instance, 10MM instead of 10, so
the American will know it's not a 10inch end wrench, much less a
30inch on a large one.  Lower case m's were not good enough either,
while English sizes were not changed to show that they are in inches.
I guess for some folks a 25x error is easy to make when measuring or
selecting tools.

Jobst Brandt
jobst.brandt@stanfordalumni.org
Palo Alto CA