Truing Bicycle Wheels

 [ nota bene: I wrote this back in '85 or so, and only found
   a copy on the Internet in '98.  I've updated it but 
    amazingly it's still pretty accurate.  It's also proof
     that you should watch what you write- it _will_ come back
      to haunt you. 
                        -Bill Yerazunis, 8-April-1998 ]

There's a book out ("Bicycle Wheels", by Jobst Brandt) that
contains both a finite-element analysis of bicycle wheels and some very
solid advice on how to tune and true (and build) your own wheels.


Advice I can offer:

1) Spokes should be tight enough so that, when plucked, they emit a
 musical note (not a buzz) somewhere below (C above middle-C).
 Some variation (to pull the rim/tube/tire into concentricity) is
 inevitable, but a spoke that won't pluck (just buzzes) is almost always
 too loose, and one that's too shrill is too tight.

 When truing a wheel, "pluck" the spokes that you are considering
 tightening/loosening, plus one extra spoke in either direction.
 Select the spokes you actually adjust to try to get all spokes
 into the low-note area of tension/tone.

2) Invest $40 or so in the machinist's tool called a "Test Indicator".
 This is a nifty little jeweled instrument that measures position/motion
 between two very nearby objects with great accuracy.  Mine is a Fowler,
 cost $37, has two jewels, and can repeatedly measure motion of .0005 inch
 (yes, one half of one thousandth of an inch, or .0127 mm for our metric
 friends).  The hitch is that it has a max range of only .060 (+- .030 inch)

 To use the test indicator- clamp the indicator's mounting bar to a
 convenient place on the bicycle (the brake post is a good place) and
 flex it around till the tip bears against the rim and the needle
 indicates approximately center-scale.  You will have to move the
 indicator between the radial and lateral truing steps (see below).

2A) There's another kind of indicator called a "dial indicator" that
 measures to within a few thousandths, over a distance of about one inch.
 Dial indicators are a little more expensive, but you may want to
 get one of those instead.

3) When truing a wheel, first true it radially- that is, get the rim-to-
 center distance to be constant (or near constant).  You want this accurate
 to within about .020 (+- .010) inch.  You can do this with the tire
 on, off, or just deflated.

 When radially truing the front wheel (no dish offset) count turns and
 always put the same number of turns (tighter or looser) on a PAIR of
 ADJACENT spokes (one will go to the left hub disc, the other goes to the
 right hub disc).  Thus, the radial truing will not greatly disturb
 whatever lateral (L/R) true remains in your wheel.

 Try not to turn any given spoke pair more than two full turns before
 having checked every other spoke pair on the wheel.  The typical
 "unit" of adjustment during radial truing is one full turn on
 a pair of adjacent spokes.

 Tighten up any spoke that's actively loose to the "barely tight" state.
 Likewise, loosen any spoke that's so tight it sounds shrill when you
 pluck it.  This will untrue the wheel somewhat but wheel truing is
 iterative and the problem will be fixed later.

4) "Relieve" the wheel by grabbing adjacent pairs of spokes on the SAME
 side and squeezing them together with the hand.  Do this with every
 pair of adjacent spokes, on both sides of the wheel. The idea is to firmly
 seat the spoke against the hub and against the rim, stretching the spoke
 just a bit and compressing out all of the play that burrs on the drilled
 holes, etc. will cause in a few miles of riding.

5) Repeat step 3 (radial truing)

6) Relieve the wheel again.  Check radial trueness.  It should be
 essentially unchanged.  Continue to check/adjust/relieve until the
 wheel remains radially true despite

7) Remount the test indicator so it indicates lateral (left-to-right)
 imperfection.  Also mount and inflate the tire to operational pressure.

8) True the wheel laterally.  Again, make adjustments only on adjacent
 pairs of spokes, and count/balance turns, but

        I) The typical adjustment during lateral truing is about
         1/4 turn.  Don't turn a spoke pair more than 1/2 turn
         before checking every other spoke pair on the wheel.

        II) for FRONT wheels, every quarter turn of a spoke
         tighter means ONE of the two adjacent spokes (which
         go to the other side of the hub) must get one quarter
         turn looser. (or you can split it- BOTH adjacent
         spokes get 1/8 turn looser).

        III) for REAR wheels, you have to compensate for the "dish"
         (the space where the freewheel goes) if it's a derailleur
         rear hub.  This compensation is typically 2:1 ::

                Each turn of a FREEWHEEL-side spoke must be
                compensated by one HALF of a turn of an adjacent
                spoke on the non-freewheel side.

        IV) You can "cheat" 1/8-turn adjustments and not compensate
         them- just don't do it more than once on any spoke on any
         adjust/relieve/test iteration.

9) "Relieve" the wheel again

10) Test and retrue lateral.

12) Keep at lateral/relieve/test until the wheel is laterally true
 within .010 (+- .005), as measured on the rim.  This makes it easy
 to adjust your brake pads for maximum effectiveness without rubbing.

13) Just for luck, recheck radial trueness.  It should be fine.


I've trued my wheels this way for a few years now.  The first time you
true them this way, it'll take a while, because all of the unbalanced
forces have to be adjusted out (expect to spend three or four iterations
in each of the adjust/relieve/test loops).  The second time goes much
faster, and the third time (for me) was just one pass each.

Another side effect is that because the spoke forces are balanced (because
you plucked the spokes while choosing a spoke pair to tighten/loosen) the
wheel will stay in true MUCH longer than a machine-built wheel will stay
true.  (machine-built wheels are never "relieved" until they hit the
road- which is why they usually go all potato-chip shaped within a few
hundred miles)

        -Bill Yerazunis

The above information provided "AS-IS", no warranties implied, and do
not represent my employer in any way.

"Where there's life, there's threat."   Who said it, what episode?