Of all of the tools in the cyclist’s tool box, a torque wrench is one of the most important. You may not use it very often, it might not be that interesting to use, but it’s importance cannot be overstated. That’s especially true if you ride carbon.
If you have any kind of carbon fibre on your bike, or use high end aluminium components, torque is one of the most important measurements you can get.
What is torque?
Torque is the measurement of force required to move something around a fulcrum. It measures the length of the handle to the centre of the fulcrum and the force used to rotate it. That measurement is calculated in Newtons.
Why it torque important on a bike?
The lighter a component is, the more delicate it is. While carbon fibre is immensely strong, it only has strength in the desired direction. For example, carbon handlebars are strong in downward and forward movement. Carbon seat posts are made strong enough to resist primarily downward movement and carbon frames can handle massive amounts of abuse in their direction of travel.
The downside with carbon fibre is when force is exerted in directions other than those they were designed for. To keep weight and cost to a minimum, carbon is layed up in a particular direction to provide strength and rigidity for daily use. Those layers can handle a lot of stress in a particular direction but can be very brittle in another.
For example, those carbon handlebars will be able to take your weight and absorb road buzz, potholes and sprint efforts because the direction the carbon has been laid provides strength in that direction. Stress them in another direction and they can become damaged very easily.
Aside from use, where stress is introduced to a component is where it is affixed to another. For example, the stem, seat post clamp or frame. A stem has to be tightened enough to hold a carbon handlebar in place, but not too tight as to crush it. That force cannot be measured by feel alone, which is where a torque wrench comes in.
You will notice that on many carbon components, there will be a measure of xNm. This is the torque measurement that can be applied to the component. So a handlebar with 6Nm next to where the stem would sit means you can tighten the stem bolts to a maximum of 6 Newtons to hold it tight and not crush the carbon.
Mark one eyeball
There are many elements of bike mechanics that we can do by eye or by feel. Accurately measuring torque is not one of them. Considering how expensive some carbon components can be and how readily available a torque wrench is, it is a no brainer as far as I’m concerned.
As an added incentive, many carbon component manufacturers will only warranty their products if the correct torque has been used. So if you do crush your expensive Vision Metron 4D bars by tightening the stem too much, tough. Vision will not cover that kind of damage.
So if you’re planning to spend £200- 300 on a carbon component, it makes sense to spend £40 – 50 on a torque wrench to maintain it. I think so anyway.