torque A turning or twisting force. Torque causes torsion, which is the twisting of a normally rigid body. In the British Commonwealth and the US, torque is commonly measured in foot pounds or inch pounds. Elsewhere, the metric system is used and torque is measured in kilogram meters or centimeter grams.
Whether measured in the English or metric system, the formula for torque is the same:
Torque = Length x Force
- Foot pound: Abbreviated ft. lb. The amount of force applied in the direction of turning by one pound on a one foot lever. It is the usual measurement for torque in the British Commonwealth and the US. An inch pound is the smaller unit of torque measure, and is often used with bicycles. The foot pound is analogous to the kilogram meter of the metric system.
foot pounds to:
Inch pounds 12 Kilogram meters 0.138 255 Grams centimeter 13.855 5
- Gram centimeter: Abbreviated gcm. The smaller metric unit of torque, analogous to the English inch pound. It is the amount of force applied by one gram applied to a one centimeter lever.
To convert grams
Foot pounds 0.067 196 848 Inch pounds 0.005 599 741 5 Kilograms meter 0.1
- Inch pound: Abbreviated as in. lb. A measurement of torque equal to one twelfth of a foot pound, that is, the amount of force applied in the direction of turning by one pound on a one inch lever. Inch pound measurements are generally used on bicycles.
Foot pounds 12 Grams centimeter 178.579 67 Kilograms meter 17.857 967
- Kilogram meter: Abbreviated kgm. The standard metric measurement of torque. A kilogram meter is the amount of force applied by one kilogram on a one meter level. A gram centimeter is more commonly used with bicycles.
To convert kilogram
Foot pounds 7.233 01 Grams centimeter 100,000 Inch pounds 72.330 1
- Slip angle torque: Steering trail creates slip angle torque when the wheel is turned to the side and a load is generated on the contact patch of the tire that tries to push the tire back in a straight line. Slip angle torque increases with speed and this makes the steering more stable.
- Torque screwdriver: A screwdriver that measures how much twisting force is applied to a screw. The shaft is designed to twist under load and read out on a scale attached to the handle. Rarely used with bikes.
- Torque wrench: A tool for measuring torque. The most common type measures torque directly onto a scale with an indicator needle. A second, more accurate, type is pre-set to the desired torque and clicks when that is reached. Torque wrenches are expensive and to maintain accuracy should be treated gently and recalibrated from time to time. Time and experience can give one a good feel for how much to tighten a bolt, but on sensitive or very expensive gear you might want to go to your local bike shop and have them use their torque wrench.
- Torquing technique: One uses a torque measurement on a threaded fitting to ensure a correct clamping force, but a torque wrench or torque screwdriver measures the resistance to turning, not clamping force. Poorly made, damaged, unlubricated, or dirty threads may not give a correct torque measurement because you will be measuring turning resistance, not clamping force.
It is important to use the torque specified for a part since three factors are taken into consideration determining the correct torque.
- To properly secure the part so it will perform correctly.
- To avoid damage to the part by overtightening.
- To get the maximum clamping force without fastener failure.
With correctly torqued parts, the threads give slightly and exert a pulling back force that gives the greatest clamping power. If a part is overtorqued, the threads are stressed past their point of resilience and the result may actually be less clamping force as the elasticity of the threads degrades. In other words, more torque is not always more clamping power, and can actually decrease clamping power.
Properly prepare parts before torquing. Make sure that the threads turn in the correct fashion. If there is any untoward binding, clean the threads. When using a torque wrench or torque screwdriver, apply pressure with a steady even force.