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Wheel Tension Measurement

This article with discuss the use of the TM-1 Spoke Tension Meter. See also related articles:

The TM-1 can be used to accurately and reliably measure the tension of each spoke in a wheel. The TM-1 will also measure the average tension of all the spokes in a wheel, and the relative tension between all the spokes in the wheel. It works on nearly any bicycle spoke, no matter what the diameter, material, or shape. The TM-1 Tension Meter is a precision measuring instrument and should be used and stored with care. To avoid damage, it is recommended that the TM-1 be stored in its original packaging or suspended from a bench hook. It should always be kept clean and dry. As new spokes are developed, check the TM-1 Tension Meter page for updated reading conversion tables.

NOTE: The TM-1 Tension Meter includes a printed table to convert tension reading to kilograms force. Because of new and varied steel bladed aerodynamic spokes, there is a webpage that acts as a chart calculator for steel bladed spokes not on the table. See the TM-1 Tension Meter Bladed Spoke Calculator here.

Wheels that are strong, reliable and long-lasting have spokes that are properly tensioned. Tension is the amount of force pulling on a wheel's spokes. Spokes that have low tension will continue to loosen as the bike is ridden, resulting in shortened spoke life and a wheel that requires continuous re-truing. As the wheel rotates while in use, the spokes that are on the bottom next to the ground actually lose tension momentarily. This loosening each revolution is a "stress cycle", and low tension wheels actually see a greater stress cycle than wheel with relatively greater tension. A high stress cycle fatigues the metal and leads to spoke breakage.

Spokes that have too much tension can result in deforming and/or cracks near the nipple holes of the rim, as seen in the image below. Notice crack at red arrow.

Rim failure for over tension

Too much tension can also lead to failure of the hub flange. The wrench flats of the spoke nipple can become deformed and rounded by forcing the nipple to turn while the spoke is at too high tension.

In addition to achieving proper spoke tension, it is also important for all the spokes in the wheel to have approximately the same relative tension. Relatively great differences in tension between each of the spokes will result in a wheel that is not laterally stable and that will come out of true more easily and more frequently.

The recommended tension for spokes in bicycle wheels can be as low as 80 Kilograms force (Kfg) and as high as 230 Kilograms force. As a rule of thumb, it is best to set tension as high as the weakest link in the system will allow, which for a bicycle wheel is usually the rim. Therefore, to obtain a spoke tension recommendation for a specific wheel, it is best to contact the rim manufacturer.

Rim true, or run-out, is dependent upon spoke tension and on the original manufacturing tolerances of the rim hoop before the wheel is even built. Good quality rims may vary in round less than 1mm before being built.

Measuring Tension of a Spoke

 

  1. Measure the diameter of the spoke using the included spoke diameter gauge. The smallest slot the spoke fits into determines the diameter. A measuring caliper can also be used to measure the spoke diameter. The diameter at the middle section of spoke will determine the appropriate spoke-type column on the Conversion Chart.
  2. Squeeze the TM-1 at the handle grips (ref. #17). Place the spoke between the two fixed posts (ref. #3) and the moveable post (ref. #4). Gently release handles. With butted spokes, position the posts so they rest on the narrowest portion of spoke. With aero/bladed spokes, position the posts so they rest against the wide, flat side of the spoke.

    Squeeze tool and engage

    Release tool and read

  3. With the TM-1 engaged on the spoke, the pointer (ref. #14) will be pointing to a number on the tool's graduated scale. This number is a deflection reading that is used in conjunction with the TM-1's conversion table to determine the actual tension of the spoke.
  4. Using the conversion table, find the column corresponding to the material and diameter of the spoke being measured. Follow the column down to the row corresponding to the spoke's deflection reading (as determined in step 3). The number at this intersection is the actual tension of the spoke in Kilograms force (Kgf).

The TM-1's conversion table converts the tool's deflection reading into Kilograms force. Other units of force sometimes used are Newtons and pounds force. One Kilogram force is approximately equal to 10 Newtons or 2.2 pounds force. As an example, a spoke tension is 105 Kgf. This spoke would be equal to approximately 1050 Newton or 210 pounds force.

The conversion table is based on the diameter and size of the spokes. The table does not refer to "gauge" sizes, commonly used in the bicycle industry. Gauge systems are arbitrary assignments of numbers to the relative size of the wire or material. Gauge sizes are often used for sheet metal, needles, shotgun size, and wire. There are several systems used depending upon the specific industry. For example, in the electrical industries, wire gauge is determined by a formula based on resistance per unit length. In the wire weave industry and the bicycle industry, the gauge system is Washburn & Moen Company, where the numbers are arbitrary and have no particular meaning other than relative size. The gauge system can be confusing because the size of the wire diameter decreases as the gauge numbers get larger. Relatively smaller gauge numbers mean a relatively larger wire.

Gauge systems often result in confusion for manufactures and users. Two well known spoke manufacturers give different millimeter diameters for what they both call "16 gauge" spokes. Because of this, it is best to simply use the measured diameter sizing of the spoke. The TM-1 conversion chart has tension columns for different spoke diameter, measured in the middle of the spoke where the TM-1 engages.

For bladed spokes, measure both the thickness and width of a blade (major and minor measuresements). When taking a TM-1 reading measurement on a bladed spoke use care to hold to the tool square to the blade profile. If the tool is held crooked it will not give an accurate reading.  NOTE: If the chart does not have the correct size of steel bladed spoke, use the Bladed Spoke Calculator.

Bladed spoke alignment

 

Measuring Average Spoke Tension

The average tension is the sum of the individual spoke tension measurements, divided by the number of spokes measured. Each wheel has two averages, one for the left side spokes and one for the right side spokes. If the spoke hole flanges of the hub are centered between the locknuts of the hub, it is possible for the left and right sides to have nearly equal average tension. However, if the spoke hole flanges are not centered between the locknuts of the hub, the tension between the left and right flanges will vary. Generally, on most rear wheels, the gear side (right side) will have greater tension then the left. On front wheels with disc brake mounts, the disc side will have more tension.

 

To determine average tension:

  1. Take deflection readings of all the spokes on the right side of the wheel. Record these numbers.
  2. Add the recorded numbers together.
  3. Divide the sum of the recorded numbers by the number of spokes measured. This number is the average of the deflection readings.
  4. Use the conversion table to convert the average deflection reading into the average spoke tension in Kilograms force.
  5. Repeat steps 1 - 4 for the left side of the wheel.

Using the TM-1 Tension Meter Conversion Table

The Coversion Table may be downloaded as an Adobe® PDF file here.  NOTE: New steel bladed spokes of various dimensions are always entering the market. For bladed steel spokes not on the Coversion Table, use the Bladed Spoke Calculator to generate unique tension columns.

The TM-1 is calibrated for 16 different types of spokes. Round steel spokes are calibrated regardless of brand. Some of the bladed on odd sizes are proprietary designs, and these are noted below. The blade sizing is based on measurement, not on manufacturers nominal names:

  • 2mm round steel
  • 1.8mm round steel
  • 1.7mm round steel
  • 1.6mm round steel
  • 1.5mm round steel
  • 2.3mm round steel
  • 2.6mm round carbon (Spinerg® Spox)
  • 2mm round titanium
  • 3.3mm round aluminum (Mavic® Zircal)
  • 3.2mm x 1mm bladed steel (DT® New Aero)
  • 2.6mm x 1.4mm bladed steel(Shimano® blade)
  • 2.1m x 1mm bladed steel (Sapim® CX Ray)
  • 2.2m x 1.4mm bladed steel (DT® Aero Speed)
  • 2.6m x 1.3mm bladed titanium (Cane Creek®, Marwi®)
  • 4.3mm x 2.1mm bladed aluminum (Mavic®)
  • 5.3mm x 1.8mm bladed aluminum (Mavic®)

Below is a simplified table showing only three spokes. The deflection readings that are read off the tool are the left most column. The corresponding kilograms force is listed below each spoke diameter.

TM-1 Deflection Reading 2mm Round Steel 1.8mm Round Steel 3.2mm x 1mm Bladed Steel
14 - 53 97
15 - 58 107
16 - 64 119
17 53 70 132
18 58 77 148
19 63 85 165
20 70 94 -
21 77 105 -
22 86 117 -
23 96 131 -
24 107 148 -
25 120 167 -
26 135 - -
27 153 - -
28 173 - -
29 - - -

 

Notice that there may be some blanks for extreme low and high readings. If a 2mm spoke reads 16 or less from the tool, the tension is below 51 Kilograms. This spoke would be quite loose. However, a 3.2mm x 1mm bladed steel spoke is 89 kgf when the tool reads 14.

The table does not include separate columns for butted spokes. In testing spokes at the Park Tool Company, it was determined there was no sigfinicant difference between straight diameter spokes and butted spokes. A butted spoke is basically considered a shorter straight gauge spoke.

The pointer of the tool will point at a number on the scale. For more accurate tension results, the tool can be read to finer precision. If the point repeats just off a number, the reading can be quartered. For example, the image below shows an example of a 24, a 24.5, a 25 and a 25.25. The 25.25 show the pointer just off the 25 mark.

Finer reading of the TM-1

Tension Balancing and Relative Spoke Tension

Relative tension is the tension of a spoke in comparison to the tension of one or more other spokes. A wheel with spokes that are within plus or minus 20% of the wheel's average spoke tension is generally considered to have acceptable relative tension. As explained above, the spokes on one side of a wheel may be tensioned differently than the spokes on the opposite side. Therefore, it is important to only compare the tension of a spoke relative to spokes on the same side of the wheel. To determine relative tension:

  1. Determine the average tension of the spokes on the right side of the wheel.
  2. Multiply the average tension by .8 and by 1.2. The resulting two numbers will provide the acceptable relative tension range.
  3. Use the TM-1 to take deflection readings of each individual spoke and use the conversion chart to convert the readings into individual tension measurements.
  4. Determine if the individual tension measurements fall within the acceptable relative tension range from step 2.
  5. Repeat steps 1 - 4 for the left side of the wheel. If the spokes are not within the acceptable range of relative tension, adjustments need to be made to the tension of the spokes.

Tension Recommendations

Rim manufacturers have set tension recommendations from as low as 80 Kilograms Force to as high as 230 Kilograms force. Generally, the heavier and strong the rim, the more tension it can handle. A light rim may be weight from 280 grams to 350 grams. A heavy rim may be said to weigh 450 grams or more. Additionally, rim eyelets may help distribute the load on the rim wall. A lack on eyelets on a light rim may imply less spoke tension is required. Always consult the rim manufacture for the most up to date specifications. Note that these manufactuers give specification for the wheel without tire, or without inflated tire. Tire pressure will have the effect of lowering the tension of the wheel. Generally, do not try to account for this drop by adding more tension then recommended by the manufacturer.

Below are some specifications:

Brand or Manufacturer Model Front wheel
NOTE: measure rotor side
if a disc hub
Rear Wheel- right side (chain side)
Bontrager® Race X Lite Aero Carbon 91 to 136 Kgf 122 to 181 Kgf
  Race X Lite Aero 91 to 136 Kgf 122 to 181 Kgf  
  Race X Lite 94 to 136 Kgf 122 to 181 Kgf
  Race Lite Tandem 100 to 159 Kgf 100 to 150 Kgf
  Race Lite 77 to 127 Kgf 86 to 159 Kgf
  Race X Lite ATB 50 to 132 Kgf not availabe
  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
50 to 132 Kgf 50 to 132 Kgf
  Superstock 29-inch Disc Compatible 54 to 132 Kgf 54 to 132 Kgf
  Superstock Disc Compatible 54 to 132 Kgf 54 to 132 Kgf
  Superstock 54 to 132 Kgf 54 to 132 Kgf
Campagnolo® Eurus Wheel 60-80 Kgf 95-115 Kgf
  Neutron Wheel 60-70 Kgf 120 to 140 Kgf
  Hyperon Wheel 60-80 Kgf 110 to 130 Kgf
  Proton Wheel 50 to 70 Kgf 120 to 140 Kgf
  Scirocco Wheel 60 to 80 Kgf 85 to 105 Kgf
  Zonda tangent spokes 60 to 80 Kgf
radial spoke 75 to 95 Kgf
90 to 110 Kgf
Mavic® Crossride® Ceramic 70 - 90 Kgf 70 - 90 Kgf
  Crossride® Disc 90- 125 Kgf 115 - 145 Kgf
  Classics SSC® 80 - 100 Kgf 80 - 100 Kgf
  Crossroc® UST®, Crossroc UST® Disc 90 - 120 Kgf 90 - 120 Kgf
  Cosmic® Elite 110 to 140 kgf 110 to 140 kgf
  Ksyrium® Elite 100-130 Kgf 120-145 Kgf
  Ksyrium SSC 90 - 110 kgf 130 - 150 kgf
 

Crossmax SL Disc 07
and SLR Disc

110 -145 kgf 115 - 150kgf
  Crossmax® ST Disc 115- 150 Kgf 115 - 150 Kgf
 

Crossmax ST

105-150 kgf 115-150 kgf
  Crossmax SLR Disc LEFTY 110 - 145 kgf ---
  Crossmax® SLR 100 - 130 kgf 115 - 150 kgf
  Crossmax® SX 105 - 150 kgf 105 - 150 kgf
  Crosstrail &
Crosstrail Disc
90-125kgf 110-140kgf
  Cosmic® Carbone SL Premium ® 105-145 kgf 120-160 kgf
  Cosmic® Carbone SSC® --- 130-150 kgf
  Cosmos® --- 100-120 kgf
Shimano® Wheels WH-M959, WH-M575, WH-M540 98 to 118 Kgf 105 to 128 Kgf
  WH-M7701 (also for carbon) 105 to 160 Kgf 98 to 140 Kgf
  WH-7700 and 6500 98 to 118 Kgf 105 to 128 Kgf

 

Calibration

The TM-1 Tension Meter is calibrated at the Park Tool manufacturing facility. Generally we do not recommend readjustment of tool. If the tool is worn or damaged and appears to be inaccurate, return to Park Tool for recalibration. Park Tool will recalibrate and return the tool for a reasonable charge.

It is recommended for professional mechanics and service departments use a non-riding wheel to help in tool calibration. Remove the axle from a wheel so that it is not rideable. Mark a spoke as a reference spoke and measure this one spoke. Write the date of the measurement directly on the rim. This same spoke can be used to double check the original calibration. If the tool is reading different than this "reference spoke", the spring tension can be changed. If the tool is reading low, take the tool off the spoke and turn it upside down. Remove the spring from the fixed moving stud, and then thread the adjusting screw inward toward its stud. This will decrease tension on the TM-1 spring, resulting in a higher deflection reading. If the TM-1 is reading high, increase tension at the adjusting screw.

Special Thanks

The Park Tool Company would like to thank Colin S. Howat of the KTL Lab, Lawrence, Kansas, for his assistance and help in developing the TM-1 and the conversion table.