Park Tool TM-1 Instructions Manual
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5115 Hadley Ave. N., St. Paul, MN 55128 (USA) www.parktool.comPARK TOOL CO.5115 Hadley Ave. N., St. Paul, MN 55128 (USA) www.parktool.comPARK TOOL CO.TM-1 Tension MeterThe TM-1 can be used to accurately and reliablymeasure the tension of each spoke in a wheel, theaverage tension of all the spokes in a wheel, and therelative tension between all the spokes in the wheel.It works on nearly any bicycle spoke, no matterwhat the diameter, material, or shape.SPOKE TENSIONWheels that are strong, reliable and long-lastinghave spokes that are properly tensioned. Tension isthe amount of force pulling on a wheel’s spokes. Spokes that have low tensionwill continue to loosen as the bike is ridden, resulting in shortened spoke lifeand a wheel that requires continuous re-truing. Spokes that have too muchtension can result in deforming and/or cracks near the nipple holes of the rim,around the flange of the hub, and at the wrench flats of the spoke nipple.In addition to achieving proper spoke tension, it is also important for allthe spokes in the wheel to have approximately the same relative tension.Relatively great differences in tension between each of the spokes will resultin a wheel that is not laterally stable and that will come out of true moreeasily and more frequently.The recommended tension for spokes in bicycle wheels can be as low as 80kilograms force (kgf) and as high as 130 kilograms force. As a rule of thumb, itis best to set tension as high as the weakest link in the system will allow, whichfor a bicycle wheel is usually the rim. Therefore, to obtain a spoke tensionrecommendation for a specific wheel, it is best to contact the rim manufacturer.MEASURING TENSION OF A SPOKE1. Measure the diameter of the spoke using the included spoke diametergauge. The smallest slot the spoke fits into determines the diameter. Forbutted spokes, measure the narrowest portion of the spoke. A measuringcaliper can also be used to measure the spoke diameter.2. Hold the TM-1 horizontally (flat). Squeeze the TM-1 at the handle grips(ref. #17) as in Picture 1. Place the spoke between the two fixed posts(ref. #3) and the moveable post (ref. #4) as in Picture 2. Gently releasehandles. NOTE: With butted spokes, position the posts so they rest on thenarrowest portion of spoke. With aero/bladed spokes, position the postsso they rest against the wide, flat side of the spoke.3. With the TM-1 engaged on the spoke, the pointer (ref. #14) will be pointingto a number on the tool’s graduated scale. This number is a deflectionreading that is used in conjunction with the TM-1’s conversion table todetermine the actual tension of the spoke.4. Using the conversion table, find the column corresponding to the materialand diameter of the spoke being measured. Follow the column down tothe row corresponding to the spoke’s deflection reading (as determinedin step 3). The number at this intersection is the actual tension of thespoke in kilograms force (kgf).* Other units of force sometimes used are Newtons and pounds force. Onekilogram force is approximately equal to 10 Newtons or 2.2 pounds force.MEASURING AVERAGE SPOKE TENSIONThe 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 holeflanges of the hub are centered between the locknuts of the hub, it is possiblefor 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,such as on most rear wheels and front wheels with disc brake mounts, it isnot possible to have the same tension between left and right side spokes.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 spokesmeasured. This number is the average of the deflection readings.4. Use the conversion table to convert the average deflection reading intothe average spoke tension in kilograms force.5. Repeat steps 1–4 for the left side of the wheel.MEASURING RELATIVE SPOKE TENSIONRelative tension is the tension of a spoke in comparison to the tension of oneor more other spokes. A wheel with spokes that are within plus or minus20% of the wheel’s average spoke tension is generally considered to haveacceptable relative tension. As explained on page 3, the spokes on one sideof 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 tospokes 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 numberswill provide the acceptable relative tension range.3. Use the TM-1 to take deflection readings of each individual spoke anduse the conversion chart to convert the readings into individual tensionmeasurements.4. Determine if the individual tension measurements fall within theacceptable relative tension range from step 2.5. Repeat steps 1–4 for the left side of the wheel. If the spokes are notwithin the acceptable range of relative tension, adjustments need to bemade to the tension of the spokesNOTES:These instructions provide basic information for using the TM-1 TensionMeter. For a thorough discussion on use of the TM-1, as well as updatedcalibration tables and information on a variety of wheel topics, visit the ParkTool web site: (www.parktool.com).The TM-1 Tension Meter is calibrated at the Park Tool manufacturing facility.Do not readjust the spring, spring adjustment screw or any other parts. If thetool is worn or damaged and appears to be inaccurate, return to Park Tool forrecalibration. Park Tool will recalibrate and return the tool for a reasonable charge.The TM-1 Tension Meter is a precision measuring instrument and shouldbe used and stored with care. To avoid damage, it is recommended that theTM-1 be stored in it’s original packaging or suspended from a bench hook. Itshould always be kept clean and dry.TM-1 Instructions / Instructions / Anleitung / Instrucciones1 2 |
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