Nerd Talk: The Merits of Torque Wrenches

Berk Bonebonce

Do you think there is a single pro mechanic who actually owns one of these?

I've had about 30 years of messing around with mostly high-end bike kit, and I have always found torque settings to be quite intuitive. Experience gives you a 'feel for things' and tightening to the correct torque is really a matter of common sense. Common sense means I don't need to refer to a manufacturers guide for the correct torque.

Or do you think torque wrenches are an essential piece of kit?

Interesting article here: http://www.bikeradar.com/gear/article/w ... able-24917

meanredspider

I don't think torque can in any way be described as "common sense". There's something to be said that a ring spanner or allen key will be of a size that limits the torque you can apply by hand but there are lots of situations in engineering where the torque to be applied has nothing to do with the size of the fastener. To complicate things further, the pitch of the thread has a big infuence on the clamping force for any particular applied torque - I'm not sure how common sense can determine the different torques needed for differing pitches - especially where the applied torque is related to end-float rather than clamping force.

When bikes used to be heavy, brutal things (some BSOs are still) then, yes, do it up "tight". The far more sophisticated modern kit needs a sophisticated approach in some key areas.

White Line

There was some article on here about the Astana mechanics at the Tour this year or last year - can't remember when. I was saying something about how Contador's mechanic used a torque wrench on everything. Even brake pads.

nicklouse

Berk Bonebonce
in a word Yes. Most of them.

Anonymous

I got one. Use it on everything now. Even the wife.

balthazar

They never used to, when most fittings on a bike were metal rather than carbon. Still, even then torque wrenches would have been a good idea for some fixings — like old-style press-fit cranks, which are invariably grossly under-tightened, even by experienced mechanics. Had they consented to using a torque wrench periodically, I suspect many crank failures could have been avoided. Similarly, occasional use of a spoke tensiometer might have saved a few wheels.

That said, it strikes me as a bit overweening to depend on them for ordinary attachment fixings, as is the modern fashion. If the components have such a narrow range of acceptable torque values, then I think that it a design failing; in any case, a torque wrench only tells half the story.

giant_man

White Line wrote:

There was some article on here about the Astana mechanics at the Tour this year or last year - can't remember when. I was saying something about how Contador's mechanic used a torque wrench on everything. Even brake pads.

I would hope so too. I wouldn't be without one.

k-dog

I read a study a while ago where they looked at experienced mechanics who thought that they could feel the right torque - and the conclusion was that they were all miles off.

Rodrego Hernandez

I've just serviced a bike that was maintained by a pro-tour team mechanic and it was obvious that they just tighten everything to within an inch of its life. For example, the cap that screws in to the dura ace chainset / axle was done with a wrench and was not coming back out, these are supposed to be hand tight and flush, not recessed into the crank arm by 3mm!

To answer the question, some do, some don't, all should.

nicklouse

Rodrego Hernandez wrote:

I've just serviced a bike that was maintained by a pro-tour team mechanic and it was obvious that they just tighten everything to within an inch of its life. For example, the cap that screws in to the dura ace chainset / axle was done with a wrench and was not coming back out, these are supposed to be hand tight and flush, not recessed into the crank arm by 3mm!

To answer the question, some do, some don't, all should.

I wonder which "bolt" this was. as there are non on that crank that state they should be "flush" (Presuming a current crankset)

the pre-load bolt? or the pinch bolts?

if the pre-load bolt I hope you did undo the pinch bolts before trying to undo it.

Rodrego Hernandez

nicklouse wrote:

Rodrego Hernandez wrote:

I've just serviced a bike that was maintained by a pro-tour team mechanic and it was obvious that they just tighten everything to within an inch of its life. For example, the cap that screws in to the dura ace chainset / axle was done with a wrench and was not coming back out, these are supposed to be hand tight and flush, not recessed into the crank arm by 3mm!

To answer the question, some do, some don't, all should.

I wonder which "bolt" this was. as there are non on that crank that state they should be "flush" (Presuming a current crankset)

the pre-load bolt? or the pinch bolts?

if the pre-load bolt I hope you did undo the pinch bolts before trying to undo it.

Yeah, the thing that screws into the bottom bracket axle, whatever it's called. Of course the pinch bolts were undone! Rather than use the tool that you use to tighten by hand, they must have used one attached to a wrench. It should be just about flush with the crank arm, not recessed into it.

rake

the more spannering you do the more feel you seem to get. wrenches are very good and the correct way to do the job but i wouldnt say they are essential for everyone with a bike carbon or not. i can feel when the carbon stem starts to grip and become firm and then go a little more. it will be less than maximum but enough to hold firmly in place with any steering input. im not saying i can accurately estimate torque, but tighten suficiently to hold the part in place.

Monty Dog

For someone whose spent many years of my career designing and building complex engineering products, you simply cannot assembly highly-engineered products without one. Composite materials and lightweight alloys do not respond well to being over-stressed - by all means continue to ignore instructions, just be prepared for unexpected breakages, particularly for things like carbon bars, stems and seatposts. Whilst I have a big torque wrench, I generally don't bother with things like cassette lockrings, cranks bolts or cartridge BBs except when doing new builds for others.

rake

i agree, but my parts will be under tightened if anything as i go just past the point of where they start to move with a good pull, if this is too tight then the part isnt strong enough to hold anyway but yes with complex engineered equipment the correct way is to wrench it, ive worked on cylinder heads and always used one, im just avoiding the expense. I know a new frame will cost more.

sungod

former protour mechanic says "yes"

http://velonews.competitor.com/2010/11/ ... ter_149059

Berk Bonebonce

More affordable torque wrenches = greater uptake in use.

balthazar

Berk Bonebonce wrote:

More affordable torque wrenches = greater uptake in use.

But they've become objects of desire in their own right, haven't they? Now a bikie is nobody if he doesn't know the error deviation in the scale against which his titanium nitrided wrench was calibrated..! Blokeish one-upmanship is limitless.

Rodrego Hernandez

If I was just maintaining my bike I'd be happy going by feel. Maintaining other bikes, I'm happier doing it by the book - if there's a problem, I sleep soundly knowing I did it all by the book. If there was a problem and I had winged it and done it by feel there is no way I'd be able to sleep.

Monty Dog

Ritchey Torqkey for £12 - I have one of these and it's easy to put in your bikebag and just check the stem and seatpost bolts. It's preset to 5Nm so suits most parts.

Berk Bonebonce

More litigious (if that's the right term) world = greater uptake of torque wrenches.

Tinker with bikes for a living, and especially the bikes the pro's ride, and then you are going to 'cover yourself' by using a torque wrench. And then when Contador's bars fail: "Nothin' to do with me Guv; I tightened to the correct torque".

geebee2

I don't have one, but never had a problem ( but I haven't worked extensively ).

I think using carbon assembly paste is the important thing with carbon seatpost clamp, stem, bars. I don't have quoted torque numbers for most of these anyway, so I don't see how a torque wrench would help much.

For cable fixing bolts etc. I have just learnt how much is not enough, and use a little more. Never had a problem, except once trying to undo a 20 year old bolt that had corroded ( it sheared off - I should have applied more WD45 and been more patient ).

I would have liked one when fitting my SRAM GXP bottom bracket - but in that case, as it's a custom spanner, I'm not sure how that would work in any case. Instead I just did some fairly careful estimation with weights and lengths.

hotnajers

I recently had to buy a new BB link for my i drive 5 3 0 I removed the bolts from the flex bone to clean as and re loctite them having noticed one of the bolt threads was looking worse for wear I replaced it with one from toolbox but did not realise at the time it was of a differnt material using the reccomended torque of 8nm it snapped the head of! the torque setting is for a ss bolt. Live and learn as they say!

chrisw12

To all you torque wrench using advocates

I'll ask the same questions again. This came up in another thread and it went eerily quiet.

1) How do you know that your torque wrench is correctly calibrated?

2) What effect does lubrication have on the torque values?

3) How do the manufacturers come up with they recommended figures and what are the error or range of acceptable values?

I'd like an answer to all three by the way in one post. Question 1 should be the easy one.

flasher

chrisw12 wrote:

To all you torque wrench using advocates

I'll ask the same questions again. This came up in another thread and it went eerily quiet.

1) How do you know that your torque wrench is correctly calibrated?

2) What effect does lubrication have on the torque values?

3) How do the manufacturers come up with they recommended figures and what are the error or range of acceptable values?

I'd like an answer to all three by the way in one post. Question 1 should be the easy one.

1) Good torque wrenches come with a calibration certificate.

2) Up 20% variability apparently.

3) R&D and who knows I'm not a manufacturer!

What's your point, as has already been shown in this thread pro wrenches use them, I use one as do lots of others, rather 20% variability than complete guess work!

desweller

chrisw12 wrote:

To all you torque wrench using advocates

I'll ask the same questions again. This came up in another thread and it went eerily quiet.

1) How do you know that your torque wrench is correctly calibrated?

2) What effect does lubrication have on the torque values?

3) How do the manufacturers come up with they recommended figures and what are the error or range of acceptable values?

I'd like an answer to all three by the way in one post. Question 1 should be the easy one.

1. Stick and a weight?

2. You should always lubricate threads and other sliding surfaces (e.g. beneath the heads of screws) to maximise your chances of achieving the intended tensile load.

3. The recommended value will be the value that achieves the required tensile load (blindingly obvious, but you asked). The design of the component and the selection of the fastener are both contributory factors. However, as frictional effects are difficult to predict, quite a large error margin will be present (up to +/- 15%) in the target value.

Another question you could have asked was, 'how often can you re-use screws?'

nicklouse

1 you dont, but you hope that the makers have tested them to a degree and they are accurate to a % figure stated.

2 a lot.

3 failure tests. no idea but it will be easy to work out from the tables.

more reading if you are that way inclined.

http://www.roymech.co.uk/Useful_Tables/ ... ading.html


max torque settings for bolts of "X" cross section and material

http://www.engineersedge.com/torque_table_sae_ftlbs.htm

how to workout the torque for a give bolt tension load
http://www.engineersedge.com/torque.htm

more reading.
http://www.zerofast.com/torque.htm


most of the info comes from years of empirical results.

ride_whenever

AFAIK bolt torques are always given dry and you need to compensate for your grease or antiseize compound.

Many bolts are given torque ranges rather than absolute figures.

chrisw12

Are pro wrenches scientists or for that matter engineers? I've got kids in school who can measure with a ruler but it doesn't make them experts at measuring or even have an basic understanding of the potential errors involved. Because you do something and are trained to do something doesn't mean you understand what you are doing or the real reasons why you are doing it.



But thanks everyone for your answers. Seems like a lot of variability there, seems rather pointless using a such a precise instrument. :roll:

flasher

chrisw12 wrote:

Are pro wrenches scientists or for that matter engineers? I've got kids in school who can measure with a ruler but it doesn't make them experts at measuring or even have an basic understanding of the potential errors involved. Because you do something and are trained to do something doesn't mean you understand what you are doing or the real reasons why you are doing it.

20% is massive, couple this to the error that might occur in my question 3 and it could suggest that you'd be better off 'with 'guess work' or at the very least 'common sense'

So would you like one of your school kids to be tightening up the bolts on your 5 grand bike by guess work and common sense?

From my experience common sense isn't actually that common!

chrisw12

nicklouse wrote:

1 you dont, but you hope that the makers have tested them to a degree and they are accurate to a % figure stated.

2 a lot.

3 failure tests. no idea but it will be easy to work out from the tables.

more reading if you are that way inclined.

http://www.roymech.co.uk/Useful_Tables/ ... ading.html


max torque settings for bolts of "X" cross section and material

http://www.engineersedge.com/torque_table_sae_ftlbs.htm

how to workout the torque for a give bolt tension load
http://www.engineersedge.com/torque.htm

more reading.
http://www.zerofast.com/torque.htm


most of the info comes from years of empirical results.

I'm not that interested but I did read this in the bottom link:-

'..."What torque should I use to tighten my bolts?" Keep in mind this is only an estimated value. It may provide satisfactory performance, but it also may not. Every application should be evaluated on its own to determine the optimum torque value for each application....'

So good luck to all you guys putting blind faith in your torque wrenches. I'll stick to 'experience' it seems to be less random.

chrisw12

Flasher wrote:

chrisw12 wrote:

Are pro wrenches scientists or for that matter engineers? I've got kids in school who can measure with a ruler but it doesn't make them experts at measuring or even have an basic understanding of the potential errors involved. Because you do something and are trained to do something doesn't mean you understand what you are doing or the real reasons why you are doing it.

20% is massive, couple this to the error that might occur in my question 3 and it could suggest that you'd be better off 'with 'guess work' or at the very least 'common sense'

So would you like one of your school kids to be tightening up the bolts on your 5 grand bike by guess work and common sense?

From my experience common sense isn't actually that common!

If i could afford a 5 grand bike, I wouldn't be teaching the school kids let alone letting them near the bike.

but fair point, perhaps we should replace common sense with 'experience'.?

oh and to add I would trust no one with my bikes (whatever the price) and always check them over on the rare occasions that they have work done on them at the lbs, as I'd imagine most people on here do.