IV. Wheel-Rim Marking

1. General instructions

    Use a black Sanford Sharpie Permanent Marker to create very permanent marks on the rim. Red can be used to designate smaller divisions. Designate a zero spoke on the same side of the wheel as is desired for the computer sensor. (With some mountain bikes do the opposite.) Assign increasing values in an anticlockwise direction as viewed from the right-hand side of the wheel and clockwise from the left-hand side. (If it is found that the wheel has been marked in the wrong direction, simply turn it around in the forks.)

    Time to mark a rim in decimal fractions of a revolution is less than 25 min. Time to mark in spoke intervals is 5 min.

 

2. Marking in decimal fractions of a revolution

     Marking the rim requires estimation of 1.6 and 0.8 of a spoke interval for a 32-spoke wheel and 0.5, 0.6, 0.7, 0.8, and 0.9 for a 36-spoke. These can be measured accurately on a card and the card used repeatedly or simply eye-balled.

(i) 32-spoke wheel

    Mark the first divisions using the following precise correlations:

Spoke        0            4          8          12          16        20         24        28

Rev            0        0.125    0.250    0.375     0.500    0.625    0.750    0.875  

Finally, using the fact that 0.8 spoke intervals equals 0.025 rev and 1.6 spoke intervals equals 0.050 rev, work on either side of the first marks until the whole rim is marked in divisions

(ii) 36-spoke wheel

        Mark the first divisions using the following precise correlations:

Spoke            0            9            18            27

Rev            0.00        0.25         0.50          0.75

Finally, work on either side of the first marks until the whole rim is marked in divisions of 0.025 rev using the following correlations:

Spoke interval        4.5            3.6            2.7            1.8            0.9

Rev interval            0.125         0.100        0.075        0.050        0.025

 

3.  Marking in spoke intervals

     Marking a rim in spoke intervals is very fast and subsequent readings are very fast and accurate. Rotation can be read down to 0.003 rev equivalent to 0.06 of a count on the Jones, but the downside is that in order to correlate with meter readings in revolutions, the measurer has to divide rim readings by the number of spokes. Obviously though, this would be the method of choice when using a rented bicycle or a wheel that is only going to be used temporarily.