Take the 2-minute tour ×
Bicycles Stack Exchange is a question and answer site for people who build and repair bicycles, people who train cycling, or commute on bicycles. It's 100% free, no registration required.

I was rather surprised to find a question about choosing a torque wrench on this site. I haven't cycled for years, but many years ago when I actually cycled I would do with a set of ordinary wrenches just fine.

What bicycle maintenance tasks would require a torque wrench and can't be done with an ordinary wrench?

share|improve this question
    
I ruined a set of aluminium handlebars by overtightening the clamps. –  Mac Jun 8 '11 at 3:21
add comment

6 Answers

up vote 4 down vote accepted

I bought a torque wrench after writing off a the bottom part of a set of Fox 36's:

Fox 36 RC2 2005

Those four little bolts at the bottom hold the axle in place, and need to be tightened enough to stop it coming out, but not so much that you stress the clamp. I'd over-tightened them and apparently the fork legs had tiny cracks. The replacement legs have a metal shim to prevent over-tightening, and the design is now different - lesson learnt for me and for Fox.

The problem is that no-one buys a torque wrench when they're starting out and could really benefit from one.

share|improve this answer
add comment

A torque wrench is needed mostly for lightweight bike parts, especially at the high end.

There are several related causes:

  • with lightweight parts the manufacturer has shaved off everything that is not absolutely essential. There is no spare strength to allow for overtightening.

  • things are made very precisely now. Rather than being able to take a 250kg gorilla, the lightweight bike can take a 120kg human. And rather than be maintained by a gorilla, you need an actual bike mechanic. This is partly to save weight, and partly to shave costs. Why use 1kg of titanium where 500g will do?

  • Most people do things up until they feel the resistance change. This slight yeild in steel is non-destructive and can be repeated thousands if not millions of times. In aluminium you need to be more sensitive because the yeild limit is sharper, but with composites and lightweight metals like titanium and magnesium the change is so fast it might as well not exist. The torque limits are likely to be tight and precise.

  • to save weight more threads are cut into expensive parts. Rather than having a semi-captive nut the body of the bike/fork/wheel is threaded. Stripping it means replacing something expensive.

What this means is that the traditional steel bolt in a steel bike will work well with (say) 15-50Nm of force used to tighten it. At 15Nm it's only just tight, at 50Nm it's probably digging into the frame and it's about to strip. But a (hollow!) titanium bolt in a carbon/epoxy stem will have a torque range of 5.5-6.4Nm, and the failure mode at the high end will be the stem failing- either it will strip the thread or the clamp will snap. And the bolt is built to match - why put in a bolt that will take 10Nm of tightening when the stem will fail at 7Nm?

There are other design changes to match these - four bolt handlebar clams on stems are now commonplace where there used to be one bolt and you just bent the clamp open then forced the (curved) handlebars through it. You can't bend an aluminium clamp like that, it will fail. And splined cranks require a lot more precision than tapered one, but that precision also allows them to be lighter as well as easier to service. The days of stripped extraction threads in cranks are (hopefully) over.

share|improve this answer
add comment

I admit I never use one... Still, for certain applications, specific tightening torque is specified. Things like crank-retaining nuts, quill-stem retaining bolts... Crank bolts on models with removable chainrings... That sort of thing.

Some people have a good feel for "tight enough", but others may be ham-fisted enough to break or strip fasteners without some reference.

share|improve this answer
    
I'm a novice user. I adjusted the location of the SPD cleats on my shoes myself, and one of them later fell off. I took it to the LBS and watched him replace it ... with a big forearm and without a torque wrench. I guess I was worried about stripping something, if not the thread then the hole in the head where the Allen key fits; or of doing it so tight that I couldn't undo it again without stripping it; I ended up leaving it loose enough that it was able to work itself completely free a few days later. Those cleats get a lot of to-and-fro work. –  ChrisW Jun 7 '11 at 12:17
    
There are some parts where a torque wrench is not required, like this. A feel for what is necessary is more important. But if those soles were carbon fiber, then it would matter. In that case, having them overly tight can crack the sole, which allows movement, which works the screws lose, which lets the cleat fall off. Not to mention damaging the expensive shoes. The same is true in many other places on the bike. This is one of the few places where that damage would only be a minor safety azard, rather than a major one. –  zenbike Jun 20 '11 at 8:43
add comment

I love my Torque Wrench. It takes away the guesswork of being sure you are tight enough. I picked up one from and off brand that was calibrated in inch/lbs, and it wasn't as expensive as the park version. If you are no pro and working with carbon fiber, you need this tool.

share|improve this answer
2  
And if you are a pro, you already have this tool. If you do not, with current products, you are no pro. –  zenbike Jun 20 '11 at 8:45
add comment

I am with yourself - no need (unless you have a very expensive pro roadbike). However there are new 'carbon fibre' components that have changed since the good-old-days. These can have things such as 'helicoil' inserts glued in to them.

In the olden days it was just chainring bolts that were tricky to get right without a torque wrench. Nowadays you can do up almost every bolt to a torque level specified in the component's manual.

share|improve this answer
    
When I was in the army in the 60s, we had a lad assigned to the motor pool.. Big Texas lad. Only human being I ever saw who could strip/break off the huge bolts on things like tank and APC drive sprocket wheels..... –  M. Werner Jun 7 '11 at 20:46
add comment

Crank bolts. They need to be really torqued, but you're always wary of over-torquing, so a torque wrench provides a good confidence factor.

share|improve this answer
add comment

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.