Don't Screw Up Your Bike: Use a Torque Wrench

by Tony Marchand


The Importance of Correct Torque:
Over tightening the bolts or screws on you bicycle can lead to disastrous results. If over-tightened, bolts or costly components may break or become damaged. I've seen the bolt that holds the seat on the post break due to over tightening while the rider was on the bicycle! I've seen expensive derailleurs break and carbon fiber seat post fracture for the same reason. Don't let this happen to you. Invest in a "torque wrench." The correct torque is essential, especially in the carbon fiber age where under tightening can lead to slippage and over tightening can lead to unforeseen cracks, breaks or disaster on the road1. One should also calibrate your torque wrench to assure correct torque force. Here are several of the types commonly used in maintenance and repair2:
  • Click Wrench:

    The user can preset the level of torque using the clutch mechanism. Once the torque level is reached, the clutch then starts to slip and one hears a click sound to indicate the required level. The wrench has a screw mechanism at the bottom which when turned, compresses a spring and sets the torque strength. We'll describe how to set the torque levels in my next video. Digital torque wrenches are also available which make the settings easier. 
  • The Beam Wrench:
    This is a very simple and basic type of torque wrench. The wrench head and handle are separated by a lever arm. The lever arm has a certain level of elasticity which allows the torque wrench to bend slightly at the level of pressure. The indicator remains parallel with the arm when the torque wrench is not in
    use or no pressure is being applied. Once torque is being applied, there is a scale which moves to give a reading, much like a weighing scale with a needle pointer that indicates the weight of the product.
Measurement units:
The measure of the force applied to produce rotational motion (usually measured in foot-pounds). Torque3 is determined by multiplying the applied force by the distance from the pivot point to the point where the force is applied. Measurements of torque include pounds-foot4 (the torque created by one pound force acting at a perpendicular distance of one foot from a pivot point), pound-inch (the torque created by one pound force acting at a perpendicular distance of one inch from a pivot point) and newton-meters5,6 (the torque resulting from a force of one newton applied perpendicularly to a moment arm which is one meter long.)
Conversion table are available depending on your torque wrench and the specifications needed (see below).

  1. Torque Wrench Essential   Types and use of a torque wrench from tony10speed.com
  2. Setting Non-Digital Torque Wrench: (coming soon) How to set a non-digital torque wrench from tony10speed.com
  3. More on Torque Wrench
  4. Torque Wrench Calibration
Know your torque specs: Gathering torque data on Steel / Aluminum / Titanium is not difficult with a number of sites listed below. Torque for carbon fiber frames and parts is more difficult to obtain. Try to rely on the manufacturers recommendations for the frame or specific part. Consult your user manual, as well as the shop where you obtained your bike, or search the internet. Be sure to stop when you hear the click! Never over tighten. Torque is usually given in a range. I use the middle of the range since the high end is the point above which we can cause damage. Always check your bike for
cracks or fracture of carbon fiber at the points where bolts can be tightened. Always use the correct grease on bolts, seat posts and other components. Carbon fiber grease contains elements that prevent slippage and allow a lower torque.

Online conversion tables: References:
  1. Workshop: Why torque wrenches are invaluable   from BikeRadar
  2. 6 Types of Torque Wrenches Explained   "from do-it-yourself."
  3. Torque   from Wikipedia
  4. Pound-inch   from Wiki answers
  5. Newton (unit)   from Wikipedia
  6. Newton meter  from Wikipedia