This article with discuss the use of the TM-1 Spoke Tension Meter as used with the Tension Conversion Calculator (TCC). See also related article on TM-1 use.
The TM-1 tool includes a conversion table that lists convertions from the tool deflection reading into kilograms force on the spoke.
By using a computer, the TCC takes the information on the table and puts it in a spreadsheet. The TCC greatly speeds converting a deflection reading from the TM-1 into a tension force on the spoke. Additionally, the TCC can be used to create an visual representation showing the tension balance between the spokes of the wheel. The TCC will also allow the professional builder and mechanic to show on paper the quality of their work. Additionally, the wheel can be evaluated for problems of tension.
NOTE: The TCC is provided as a support service for the TM-1. It will not work with other tension meters other than the Park Tool TM-1. The TCC here is a working prototype, as Version 1. Park Tool will appreciate any feedback, questions, or comments. Please email info@parktool.com directly any concerns. Use subject line, TCC
The spreadsheet file works with most Windows® operating systems and with MAC OS X. The program will ask you to "Enable Marcros". Macros must be enabled for the TCC to operate. Download and save the file below.
TCC_1.xls
After downloading to your hard drive, open and enable macros. Begin by selecting the page titled Spoke Tension Record. You may need to change view if you cannot see the entire spread sheet. Select "Zoom" from "VIEW" in the tools menu. Next, select the page titled Instructions.
It is recommended that you save the file with name as given. Open the file and give it a new name for each wheel serviced using "Save As". For example, "ErikJones_rearwheel.xls". This file may then be re-open when the wheel returns for service. The file name can also include a date of service, and then changes to wheel tension can be tracked. You will need to use and be familiar with the Windows® Excel program to open and run the TCC. The program will ask you to "Enable Marcros". Macros must be enabled for the TCC to operate. It is recommended to perform a "save as" procedure and rename the file for the wheel being worked on. This file can then be opened and updated as needed.
There will be three worksheets with the TCC, which are labeled on the bottom as Instructions, Example, and Spoke Tension Record. Begin by reading the Instruction page and review the Example page before continuing with the Spoke Tension Record. It can also be helpful to write the spoke number on the rim. These marks can typically be removed by using a solvent on the braking surface.
Tension Balance with the TCC
It is useful to know if the spokes are relatively the same tension. Spokes that are too tight or too loose relative to other spokes are result in problems. However, it is unlikely the spokes are exactly the same tension. When comparing spokes when tension balancing, compare only same side spokes. In otherwords, compare right side spokes to right side spkoes, and left side spoke to left side spokes. This is especially true on rear wheels and front wheels with dish offset, such as front wheels with disc hubs. One side will be tighter than the other.
In the example below, reading were take on a 24 hole wheel, called here Wheel #1. The table shows the readings and kilogram force for each right side spoke. The right side average spoke tension was 105.8 kgf. Deviation was 10.4 kgf. If a plus or minus 20% range was desired, the range was from 84.6 kgf to 126.9 kgf.
| Spoke as Marked on Rim | TM-1 deflection reading | Kilogram force |
| Spoke 1 | 24.0 | 106.6 |
| Spoke 2 | 24.0 | 106.6 |
| Spoke 3 | 24.0 | 106.6 |
| Spoke 4 | 24.0 | 106.6 |
| Spoke 5 | 21.0 | 75.8 |
| Spoke 6 | 25.0 | 120.6 |
| Spoke 7 | 24.0 | 106.6 |
| Spoke 8 | 24.0 | 106.6 |
| Spoke 9 | 24.0 | 106.6 |
| Spoke 10 | 24.0 | 106.6 |
| Spoke 11 | 24.5 | 113.3 |
| Spoke 12 | 24.0 | 106.6 |
The graphic chart from the TCC for the right side spokes is seen below. The right side spokes are in green. The left side spokes are in blue, and are lower tension, which is common for rear wheels. The diagram forms a loop showing the relative tension. Spokes that are tighter are further from the center. Spokes that are looser are closer to the center. Generally, an even circle is desired.
For the rear wheel above to be tension balanced at a range of plus or minus 20%, the TM-1 readings would corrolate with a low of 22 to a high 25.4. The tension balance in this wheel on the left side is excellent, and is fairly reasonable on the right, except for spoke number 5, which has a reading of 21, or about 76 kgf. However, notice spoke number 6 is a reading of 25, or a kgf of about 121. Spoke 6 is within the acceptable range, but spoke 5 is low. It is possible balance the tension between spoke 5 and 6. Loosen spoke 6 a small amount, perhaps 1/4 turn. The rim is likely to become out of true at this section. Next tighten spoke 5 enough to return the wheel to trueness. This may be more or less than the 1/4 turn on spoke 6. Check the tension of spoke 5 and 6. Update the TCC. Again, it is not necessary that each spoke be the exact same tension. It is possible on some wheels to get even tighter tension balance tolerances than plus or minus 20%. For most situations and uses, a tolerance range of plus or minus 20% is completely acceptable.
In the example below, a different 24 hole wheel called Wheel #2, has struck a pot hole, resulting in a radial impact. The tension at spoke 5 on both left and right side show a drop in tension. Additionally, the rim at area shows a "flat spot", with the rim moving abruptly toward the hub at that point. This is an indication of a bent rim. Loosening the spokes 5 will not help in re-truing this wheel. If the rim is effecting the ride or brake pad placement, it should be replaced.
Wheel #3 below is showing signs of a lateral bend at spoke 5. Notice the left and right side tension lines cross. This wheel was trued by tightening left side spoke 5, and loosening right side spoke 5. The rim was bent to the right at that area. It would be best to replace this rim.
