How to objectively evaluate torque wrenches?

Question

My local bicycle group bought very nice but very expensive torque wrenches (if I can remember right they cost about €300–500). My local discount store markets them for about €50. My local auction site has them ranging from a few euros to many hundred euros.

I don't care about product recommendations. I want to know how I can objectively evaluate them. I know that even a superb one can deteriorate due to poor handling, hence my local bike group locks them. It must always be unloaded to 0 Nm after use so that the spring won't deteriorate, non-verified information. I am planning to invest in one because I tend to destroy the metallic things such as these here. If not at all possible, please let me know whether I could use any hardware store tool for bicycle things or should I invest in one marketed to bicyclists?

P.S. by torque wrench I mean the thing that shows Newton meter units.

Answer 1

Following on from Wayne's answer, there's a few things to consider:

• beam and needle, beam and dial gauge or set torque type? Needle ones are cheap and robust but not very accurate or easy to use, dial gauge is the fragile, expensive and accurate version of needle, and set torque ones are more fragile but not necessarily more accurate.

• how easy it is to set the desired torque, assuming you buy a set torque one.

• accuracy. Both how much accuracy you need, and how well the device keeps its accuracy.

• how robust it needs to be. If it's going to kept in it's protective case in a cupboard, and only used by you then any of the above will work. But if you'll be using in shared workshops other people will borrow it, so the beam-and-gauge type will not be ideal.

I only use the set torque ones because I often find that I can't easily see the dial/gauge when I'm using the wrench. My preference for evaluating accuracy is to pay of access to a decent torque wrench and do a straight comparison by hooking them together.

Edit: Wikipedia article. Pics with labels from hhh's comment:

Beam and needle type torque wrench

Beam and dial gauge torque wrench (used to get these with a mechanical dial, modern ones are all electronic - for the price you expect as much)

Click set type torque wrench - there's a scale and twist to set handle on the end of the shaft.

Answer 2

You want a torque wrench that's made for the range of torques that you expect to use. A wrench with too large a range will give you limited precision in the range you need. Basically, it will be harder to tell if you are applying the correct torque. One that's too small won't let you apply the required torque. The accuracy of the reading may also be important. For example, this wrench (which I found with a Google search so it's not a recommendation) has a range of 20 to 108 Nm with a 4% accuracy.

Some people prefer a wrench that clicks when a preset torque is reached so they know when to stop. Others feel that reading from a scale works well enough.

There's a discussion at http://www.bikeforums.net/archive/index.php/t-158418.html that may be helpful to you.

Answer 3

Set-torque wrenches are the nicest to use, but some (including mine) don't allow you to set torque when tightening a left-hand thread (left pedal, for example). Usually there's a corresponding right-hand thread to tighten at the same point in the assembly process so I do that first and just tighten the left-hand thread by feel.

As previous posters have mentioned, you probably won't find a single torque wrench capable of doing every specified torque but 20-210 Nm should be a decent 'big' wrench. You shouldn't run into any torques larger than 210 Nm but there is a lot of stuff that gets less than 20 Nm. I'd guess that it should be fine for doing the cap nuts, but of course you will need to know the specified torque or there will be no purpose in using a torque wrench anyway.

Answer 4

In case it's not obvious, this is all on the USA side of the pond, not sure if you have access to the same tool suppliers:

You'll probably want a torque screwdriver for the smaller items. AFAIK, only available as a "clicky-type" (I don't like the clicky ones for anything other than small values, on large values I use beam type torque wrenches). Snap-On makes good durable tools, especially important for anything clicky. For example, torque screwdrivers = http://buy1.snapon.com/catalog/tools.asp?tool=all&Group_ID=16437&store=snapon-store Beam types are more durable by nature, so I'll use cheaper brands (like Craftsman) for those.