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It's good to torque

Stu Bowers
11 May 2016

For the sake of your bike – and your safety – be sure to arm your toolkit with a torque wrench.

Rather than riding into a wall, the easiest way to damage your precious carbon parts is by over-tightening bolts. The fact that torque values are now written on components signifies their importance. And while over-tightening risks failure, under-tightening can be dangerous for obvious reasons. You need to tighten bolts in a controlled way, which means investing in a quality torque wrench.

‘Torque is a load or force applied around an axis, in this case turning a nut or bolt,’ says Calvin Jones of US tool giant Park Tool. ‘Torque wrenches measure the resistance of the fastener. The torque values are an indication of the amount of load, or tension, within a bolt, so a measure of the amount of tightening force it is imparting.’ 

An important consideration is that torque values are affected by friction between the mating surfaces. Damaged, dirty or rusty threads will create more friction and make the bolt more reluctant to turn, meaning it will reach the torque setting prematurely. Conversely, grease and washers reduce friction so a bolt can take more turns to reach the desired torque value. 

‘Feel is important,’ says Jones. ‘A torque wrench can’t tell if a thread is dry, cross-threaded or if a bolt has bottomed out. It measures resistance to turning, that’s all. A good mechanic will have an understanding of what the fastener is doing, and when to use caution, for example when clamping something such as a carbon handlebar, as going too tight may damage it.’

When fitting new parts, follow the manufacturer’s instructions, as they will have tested with either greased threads or washers. If you’re in any doubt, the best advice seems to be to fit bolts clean and in a lightly oiled state.

One other issue arises when there are two (or more) bolts for the same clamp, as with some stems and seat clamps. Here it is necessary to tighten the bolts bit by bit, progressively and evenly, until the torque wrench indicates correctly on all bolts.

Most torque wrenches work with a break-away mechanism that ‘clicks off’ to indicate when the desired amount of torque has been reached. Others have a friction-based ‘clutch’ that will simply slip beyond the set torque value. Regardless of how the mechanism releases, most will be similar in that the ‘bit’ can usually be switched between allen keys and torx drivers accordingly. 

Bolts on bikes can be in confined spaces, so before investing consider how you intend to use it, and the likely torque value you need to achieve. Torque wrenches can be adjustable within a range of values, or preset. Many fixtures on a bicycle recommend a torque value of 5Nm, so preset 5Nm wrenches have become popular with mechanics owing to their simplicity. 

You will require more than one setting to cover every application though, as pedals, bottom brackets and cranks, for example, require much higher tightening values. Here are a few of the preset options you might want to look at…

Clockwise from left:

Ritchey torque key set, £20,  
Bontrager torque wrench, £15.99,   Park Tool preset torque driver, £39.99,  
Specialized torque wrench, £75 (pack of three),  
Topeak Nano TorqBar DX, £54.99,  
FWE mini torque wrench, £39.99,   

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