Wheel Tension Balance App Instructions
The Wheel Tension Balance App is a web-based tool for use with the TM-1 Spoke Tension Meter. It assists the mechanic in achieving consistent overall wheel tension by analyzing and visualizing relative tension between spokes (figure 1). The Wheel Tension Balance App can also be useful when diagnosing rim and wheel damage.
Note: The statistics generated by the app are based on a factory calibration of the TM-1 Spoke Tension Meter. The values given should be used as a general guideline, as actual TM-1 readings may vary based on the care, history, and usage of any given meter.
Figure 1: Wheel Tension Balance App used on a 20-spoke rear wheel
USING THE WHEEL TENSION BALANCE APP
Setup of the app requires the use of various drop down boxes (figure 2).
Figure 2: Drop down boxes for selecting the correct parameters of a wheel
Begin on the left side of the webpage and select the appropriate option from the Material drop down menu. There are four options at this time: Steel, Aluminum, Spinnergy PBO, and Titanium.
Next, select Shape. For steel, titanium, and aluminum, there are two options: Round and Blade. Blade means a flat or "aero" shape. The Spinnergy PBO has only one option, round.
It is always best to measure spokes directly using a caliper. All measurements should be in millimeters, rounded to the nearest tenth.
For round spokes, the diameter is referred to as Thickness. Always measure spoke diameter near the center, approximately halfway between the rim and hub. The spoke may be butted or thicker at the ends, but the TM-1 will be measuring tension in the middle section.
For steel bladed spokes, enter both the Thickness and the Width. The thickness is the thinner part of the spoke, and width is the wider (figure 3). Titanium and aluminum spokes have limited pre-set blade options.
Figure 3: Width and thickness of a bladed spoke
Variance sets a target percentage range that the mechanic will allow a spoke to vary from the average tension of all spokes on the same side. Spokes outside of the range are identified with a warning icon. Variance is set to 20% by default, but the mechanic may choose 15%, 10%, or 5% for tighter tolerances.
The Target Tension Calculator is an optional box. If you know the kilogram-force (kgf) recommendation from the manufacturer or are targeting a certain kgf, enter it here and press the return key. The calculator will produce the TM-1 deflection reading equal to the kgf entered. For rear wheels or front disc brake hub wheels, the tighter side is set to the manufacturer's recommended tension.
Left Side Spokes and Right Side Spokes drop down boxes will appear. Select the correct number for each side. If the wheel has an equal number of left and right side spokes, one chart will appear. The left side readings will be plotted in blue and right side in orange. If there are a different number of spokes on the left and right sides, a chart will appear for each. The right side will be the upper chart and left side will be the lower.
When measuring spoke tension, use the valve hole as a reference. For the right side, use the first spoke to the right of the valve (clockwise) as spoke #1. Proceed to spoke #2 and continue all the way around the wheel, measuring and recording each right side spoke. Round deflection readings to the nearest half — it is not realistic to try to be more precise.
From the left side of the wheel, begin again using the valve hole as a reference, but now use the first spoke to the left of the valve (counterclockwise) as spoke #1. Doing this ensures that the right and left side spoke measurements are in relative proximity to each other. When typing in TM-1 readings, allow time for the app to process the number before typing in more. The app's speed may vary somewhat based on the quality of your internet connection.
As you fill in the Left and Right Side Spokes columns, it will display a Tension (kgf) equivalent for each TM-1 reading as well as an icon designating whether the spoke is within tolerance. A check mark indicates a spoke is within the selected variance, while an exclamation mark indicates it is out of variance.
The radar charts to the right of the TM-1 Reading fields are useful aids for visualizing where there may be spoke tension problems in the wheel. The data point at the twelve o'clock position is considered spoke #1. When the mouse cursor hovers over data points on the chart, it displays the spoke number and its tension.
In figure 4, a 28-hole rear wheel was recorded. Although the visual graph seems to show spoke #4 and #5 on the right side have problems in tension, the spokes are actually within the variance selected. All spokes have the acceptable mark and are within the plus or minus 20% range. It is normal to see some peaks and valleys, and this does not necessarily indicate an unacceptable wheel.
Figure 4: Example of a 28-hole rear wheel
If the mechanic corrects spoke tension and re-enters the reading, both the statistics and the chart will change. The RESET button will clear all data fields and let you start over.
When you have completed measuring spoke tensions and entering values into the TM-1 Reading fields, the Wheel Tension Balance App generates statistics on the wheel (figure 4).
Figure 5: Example of the wheel tension statistics
Average Spoke Tension: The total of all same-side spoke tensions divided by the number of spokes in the sample. In figure 5, the average tension of left side spokes is 59 kgf, and the right side average is 125 kgf.
Standard Deviation of Tension: The standard deviation is the amount of variation from the average. A relatively low number means spoke tensions are all relatively close to the average. A high standard deviation indicates that spoke tensions are scattered over a relatively large range of values. In figure 5, the left side spokes are more closely balanced relative to one another than the right side spokes.
X% Upper Tension Limit (kgf): The maximum kgf value that is acceptable based on the selected variance. For example, in figure 5 right side spokes above a 144 Kgf reading would exceed the selected tolerance.
TM-1 Reading at X% Limit: The TM-1 deflection reading corresponding to the kgf value of the upper tension limit. For the wheel in figure 5, spokes reading above a 29 on the TM-1 scale would be above the selected variance limit.
X% Lower Tension Limit (kgf): The minimum kgf value that is acceptable based on the selected tolerance. For example, in figure 5 right side spokes below a 106 Kgf reading would fall below the selected tolerance.
TM-1 Reading at -X% Limit: The TM-1 deflection reading corresponding to the kgf value of the lower tension limit. For the wheel in figure 5, spokes reading below a 21 on the TM-1 scale would be below the selected variance limit.
PRINT WHEELSET DATA AND SAVE
To save the work results, there are two options. There is a "SAVE" button on the lowest box. Look for the text: Your data is saved and can be view at: Below this will be a URL to copy and save to a text clipboard. To load the file with readings and setting, copy and paste this URL into a browser.
Another option is the "PRINT" button. In the print mode you may just print off a printer. Alternatively, you may select to SAVE AS A PDF to then save the PDF to your hard drive. This will not allow you to automatically load up the readings and settings.
UNDERSTANDING WHEEL TENSION
The TM-1 is a sensitive tool and will show differences in tension between spokes. However, it is not necessary to have all same-side spokes tensioned to exactly the same reading in order to produce an excellent wheel. The rim hoop may have a certain amount of tension from being rolled and joined, or simply may not be perfectly round and flat. Both of these are common issues which prevent a wheel from being perfectly balanced and true. Do not expect a perfect circle on the graph.
Figure 6 below is an example of a rear wheel that spins straight and true. However, notice that right side spoke #4 is tight, while spokes #3 and #5 are relatively lower in tension. Although the rim is spinning straight, spoke #4 is pulling too much compared to #3 and #5. In order to to balance the tension in this situation, the mechanic should loosen spoke #4, while tightening #3 and #5. However, the rim must still spin acceptably straight. There will often be a trade-off between a perfectly tension balanced wheel and a perfectly straight wheel.
Figure 6: A rear wheel that could be improved by tension balance at #4
The Wheel Tension App can also be useful in diagnosing and explaining wheel problems. When the wheel has a lateral bend in the rim, it is common to see the left and right side lines cross one another (figure 7). When a wheel has a "flat spot" from a bent rim, the spokes will be lower in tension, as seen in Figure 8.
Figure 7: Left and right side chart lines indicating a bent rim
Figure 8: A front rim showing a flat spot from impact
Rim manufacturers have set tension recommendations from as low as 80 Kilograms Force to as high as 230 Kilograms force. Generally, the heavier and stronger the rim, the more tension it can handle. A light rim may weigh from 280 grams to 350 grams, while a heavy rim may weigh 450 grams or more. Additionally, rim eyelets may help distribute the load on the rim wall. A lack of eyelets on a light rim may imply that less spoke tension is required. Always consult the rim manufacture for the most up-to-date specifications. Note that manufacturers give specifications for wheels without accounting for tires. Tire pressure effectively lowers the wheel tension, however do not try to account for this drop by adding more tension than recommended by the manufacturer.
The rim manufacturers determine the amount of spoke pulling force in either Kilograms force (Kgf) or in Newtons (N). The mechanic can roughly convert between Kgf and N using a factor of ten. For example, a rim specification of 1100N is approximately 110 Kgf. A more accurate conversion is to use a factor of 9.8, but for quick estimates a factor of ten is sufficiently precise.
Below are rim specifications from select manufacturers:
|Bontrager®||Race X Lite Aero Carbon||91–136||122–181|
|Race X Lite Aero||91–136||122–181|
|Race X Lite||94–136||122–181|
|Race Lite Tandem||100–159||100 to 150|
|Race Lite||77–127||86 to 159|
|Race X Lite ATB||50–132||—|
Race Lite 29-inch ATB, Race Lite 29-inch Disc Compatible
2003 Race Lite Tubeless, Race Lite Tubeless Disc Specific
Race Tubeless, Race 29-inch Disc Compatible
Select Disc Compatible, Select ATB
Select Hybrid, Select road
|Superstock 29-inch Disc Compatible||54–132||54–132|
|Superstock Disc Compatible||54–132||54–132|
|Crossroc® UST®, Crossroc UST® Disc||90–120||90–120|
Crossmax SL Disc 07
|Crossmax® ST Disc||115–150||115–150|
|Crossmax SLR Disc LEFTY||110–145||—|
|Cosmic® Carbone SL Premium ®||105–145||120–160|
|Cosmic® Carbone SSC®||—||130–150|
|Shimano®||WH-M959, WH-M575, WH-M540||98–118||105–128|
|WH-M7701 (also for carbon)||105–160||98–140|
|WH-7700 and 6500||98–118||105–128|
* Note: Measure rotor side if a disc hub
** Chain side