Sunday, March 15, 2009

Truing a Bicycle Wheel using a Spoke Tensiometer

I have a set of Mavic Ksyrium Elite wheels with about 700 miles on them and they needed truing. Admittedly, they are a little light for my clydesdale size, but they are great wheels when I want something zippy to ride. Because of the stress I put on the wheels I need to ensure the truing solution includes careful attention to spoke tensions so the wheel will be both stable and durable.

Normally I go right to truing a wheel and only when trued do I use a spoke tensiometer (Park Tool TC-1) to identify any issues and resolve them. This time I decide it would be fun to see what would happen if I combined the spoke tension measurements with the results from the truing stand over several iterations to true the wheel.

The first thing I needed was a means to record measurements from the tensionmeter read and truing stand. To do this I decided on a simple worksheet (click on any of the worksheets below to enlarge) that could be duplicated for each iteration. Each spreadsheet is divided into 3 areas. The top left is for entry of the spoke tensions and other values. The top right is for displaying the spoke tension in a more handy format that better shows their interaction. This area is also used to record truing stand measurements and adjustment strategy. The bottom left area provides some general numbers like average, minimum, and maximum spoke tensions.

Step 1 - (Click on Chart 1) Base line the wheel's measurements using the spoke tensiometer and truing stand. Develop a strategy to improve overall spoke tension.

The wheel has a fare amount of wobble in it both deviating left and right from true. The spread in spoke tension is high and the tension is exceeding recommended 145 max kgf.

Step 2a - (Click on Chart 2) Make the identified changes in spoke tension and re-measure the wheel. Identify deviations from true and using current spoke tensions in the affected area identify new spoke tensions.

Well, in a perfect world the wheel would be true at this point, but in the real world it is much closer now to being true and stable.

Step 2b - (Click on Chart 3) Make the identified changes in spoke tension, tighten up the truing stand calipers, and re-measure the wheel. Identify deviations from true and using current spoke tensions in the affected area identify new spoke tensions.

The wheel is getting a bit more true.

Step 2c
-(Click on Chart 4) Make the identified changes in spoke tension, tighten up the truing stand calipers, and re-measure the wheel. Identify deviations from true and using current spoke tensions in the affected area identify new spoke tensions.

Closer still

Step 2d - (Click on Chart 5) Make the identified changes in spoke tension, tighten up the truing stand calipers, and re-measure the wheel. Identify deviations from true and using current spoke tensions in the affected area identify new spoke tensions.

Only small deviations from true remain.

Step 3 - (Click on Chart 6) - Make the identified changes in spoke tension, tighten up the truing stand calipers, and re-measure the wheel. Identify any changes in the current spoke tensions that can resolve imbalances at this point.

Two adjacent spokes could be tweaked to distribute the work a bit.

Step 4
- (Click on Chart 7) Make the identified changes in spoke tension, measure radial trueness and re-measure spoke tension. Identify deviations from round and using current spoke tensions in the affected area identify new spoke tensions.

The wheel has a bit of a hop in not quite opposite the valve stem hole. It is unlikely it can be removed completely because it would create too much local spoke tension, but it can be minimized.

Step 5 - (Click on Chart 8) Make the identified changes in spoke tension and tighten up the truing stand calipers. Using the truing stand carefully make minor tweaks spoke tensions to bring the wheel into complete true. Re-valuate spoke tension to determine if they are within spec. If not correct then identify the amount to loosen or tighten all spokes.

The wheel would have been finished at this point, but for the excessive tension on several of the drive side spokes.

Step 6
-(Click on Chart 9) Make the identified changes in spoke tension. Using the truing stand carefully make the minor tweaks in spoke tension to bring the wheel into complete true. Re-measure and re-evaluate spoke tensions to verify they are within spec.

The wheel is true, stable, and hopefully able to last for some time to come!







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