Surly Munk's Surly Long Haul Trucker Bike Build: Torque wrenches

Torque wrenches have always been something I'd thought of as being superfluous to requirements: I didn't have a very expensive bike made of carbon, so had no need to be ultra careful tightening things up, and generally I think you just 'know' when something's tight enough as a rule of thumb.

Well, at least that's how I used to think until I managed to shear a seatpost clamp bolt on my CX bike... slightly annoying really because I didn't put a lot of pressure on it, but I suppose it's probably designed for more 'slight' racing frames / posts and not meant to be tightened too much.

Also I found myself struggling to release some components / bolts without resorting to some kind of 'breaker bar' solution or whacking the wrench with a hammer - specifically pedals often got 'welded' on, ditto crank bolts (doesn't help I can never remember which way the threads are on those two items, always end up looking it up!).

Anyway after that I thought I'd have a look at some torque wrenches and find out exactly how tight I was tightening these things, and how that compared to what I hsould have been tightening them to.

Bikes are quite awkward because the majority of tightening requirements are very low torque (2Nm - 20Nm), although there are a few instances where you need a lot of torque (crank bolts are usually 35Nm - 50Nm). As a result really you need two torque wrenches to be able to cover all possibilities (since low torque wrenches generally only go 'up to' about 15-20Nm, and even if you do get a wrench that says it can cover all possible ranges from 2Nm-100Nm, say, a lot of the time those smaller torques will be difficult to 'pick up' on the wrench because they're really designed for larger torque values).

So, in the end I settled on a combination of two options:

Draper 28757 3/8-inch 10-80Nm Square Drive Ratchet Torque Wrench
(~£20 at time of writing - link to Amazon item - where I got it from - here)
M Part Cycle / Bike Torque 1/4-inch Square Drive Ratchet Torque Wrench - 3-15nm - 7pc Socket Set Included
(£35 on Ebay from Tredz Bikes)

Here they are side by side:

Both of them have the same kind of 'action' for changing the torque setting - you twist the bottom of the wrench to increase or decrease the torque setting and then lock the bottom in place when you're at the setting you want to tighten to.

They also have the same kind of 'action' for indicating when the required torque setting is reached - the heads of the wrenches 'break' slightly with an audible clicking sound.

The smaller M Part wrench came in a nice little 'set' which included a number of hex ('allen key'!) bits, plus a posidrive bit (if that's what it's called, the head with a little star shape on it!). The quality of the set is brilliant though - as you'd expect for a little bit more money at £35 - each of the hex bits is set in it's own 'adapter' which then just slips straight on to the wrench and is held in place by a lovely(!) tactile push button which secures/releases the bits from the driver. I think of the two wrench this is my favourite to use, it's just so easy switching bits around and the general quality feels a bit better on it.

The Draper is still very good quality though, don't get me wrong. It feels a lot more sturdy than the smaller M Part wrench, although I suppose you'd expect that given that it has a larger driver (3/8in on the heavier duty Draper compared to 1/4in on the more gentile M Part).

I've found the Draper very good so far for tightening crank bolts with more confidence due to the larger shaft and heavier driving head, although I did have to purchase a new set of hex bits for it since I didn't have any 3/8 inch bits. I could have probably gone for just an adapter and made do with the set of bits I already had, but I figured a dedicated set for this wrench would be easier all round - and I'm glad I did this because the set I got is very nice, Laser 0593 Hex Bit Set - 3/8" 7pc, probably Taiwanese or Chinese manufactured but very decent quality for the price - ~£10.

Some minor issues I've found - the Draper wrench only measures torque for clockwise threads, so it's unfortunately not ideal for doing both sides of a crank or pedal set (since one side on each of those items is threaded anti-clockwise). This is a bit of a shame, but still being able to know how tight one of the sides is it's not hard to then move to the other side and apply roughly the correct amount of torque.

The other issue I have is actually remembering the torques required! I resorted to writing out a spreadsheet with all the torque settings for the majority of main components which I then look up on my tablet if I need to double check. I meant to trim the sheet down to size so it only contains the items I might tighten regularly and then print it out and store it in the M Part case (which has a handy little zip pocket in it!), but this printer is out of ink here, have to sort that.

FWIW I got most of my 'data' from this page:

Torque Specificaitons on BikeTutor.com

Some great resources over there, check it out.

By and large, I think I found that for components where the torque settings had to be very low, I generally tended to overtighten things - not massively, but enough. An example might be gear shifters on a mountain bike, where the torque required can be just 5Nm or so - I would probably usually hand tighten it to about 8-10Nm without thinking about it too much - which is fine and probably wouldn't do much damage, but still a lot more than it really needed to be.

At the other extreme, for high torque settings I actually generally seemed to get those about right - although to be expected maybe since the margins of error are a lot higher for things like pedals and cranks.

Would I buy them again? I'm not sure actually. They are nice tools to use for everyday tightening/loosening, but not sure I'd bother buying them again unless I decided to buy a very expensive bike perhaps or carbon based components where too much torque can be devastating.

BAH who am I kidding, of course I'd buy them again... I think I'm hooked on buying tools actually... :p It's like some kind of primordial desire I have recently to just buy tools, tools and more tools! (And even make the tool if I can't justify the cost of buying the real thing, more on that later at some point hopefully!).

Anyway, finally here are a bunch of pics of the wrenches.

Here's a picture of the M Part wrench set - the case is a fabric 'sheer' cover over a neoprene type outer case, with heavy rubber like foam holding everything in place, generally feels very decent quality (hah, forgot though, the very first time I zipped it up, the zip broke!!! actually hasn't happened again since that first time so it's all good):