1nterceptor

"At interbike 2017 PBMA hosted the Attack Torque Survey sponsored by Prestacycle. A test of a Professional's ability to naturally tighten a bolt to exactly 5.00Nm, 78% of participants stated they have worked as a Professional Mechanic. The Average Score was 6.22 Nm, about 25% in excess of the target specification. 56 people scored below the target, 97 people scored above the target. 34 people scored at least 20% below the target. 70 people scored more than 20% above the target. The lowest result was 1.41Nm - scored by more than one person. Seven participants scored within the 13's. The highest score was 13.96Nm."

Read the full post on World Bicycle Mechanic Forum's Facebook page:
https://www.facebook.com/groups/AoPB...kw6R8dvZCW3BkI

Bike Gremlin

As expected. However, for practical purposes, not one LBS in my city uses one, most not even have a torque wrench. For steel and aluminium, hand tight seems to work for 99.9% of the mechanics.

For carbon parts, I'd not risk it, but for steel and alu - I think hand tight by feel (and experience) is good enough.

Arrowana

I'm curious to try doing a test like that tomorrow. I have a fancy torque wrench, and it doesn't come out for 90% of the bikes I work on. Anything involving carbon or modern 2-piece cranksets get the torque wrench though.

Retro Grouch 

OTOH - How many threads have been posted about left side crank arms coming loose?

HillRider

And distorted square taper crank arms and loose bottom bracket cups, etc........

chorlton

I think your sample might be biased but it is or may be interesting that there is a bias towards left side cranks.

Dan Burkhart 

That's because the right crank does not transmit drive torque to the spindle as the left crank does.

dabac

Well, many ”modern” cranksets have the bb axle permanently bonded to the DS crank, which only leaves the left able to come loose.
For square taper I’ve read an explanation somewhere based on the theory that the DS, being restrained by the chain, doesn’t see forces changing direction between pedalling and coasting the way the NDS does.
Don’t remember the exact phrases, but it sounded good at the time.

chorlton

I think I am going to regret asking that one but your explanation sounds good to me. Now... about greasing the spindle before putting the arm on?

Bike Gremlin

How many of those were mounted by experienced, whether home, or proffessional mechanics would be the right question.

HillRider

When I first started working on bikes I never thought to get a torque wrench and installed bottom bracket cups (cup-and cone) and crank arms (square taper) by getting them "good and tight". Being a relatively small and light rider I never had one loosen but when I finally did get a torque wrench I was amazed how much tighter I had to go to get to the specified torque.

Newer components like stem bolts on carbon steerers, two piece crank left arms, etc. aren't as forgiving of "close enough".

Velocivixen

That’s like trying to judge a tires inflation level by squeezing the tire, IMO. what’s wrong with using a torque wrench? Is it a tool that shops don’t feel the need to spend money on?

Sal Bandini

No need for a torque wrench. Just use the German standard of Gudentite.

Iride01 

Though a torque value is specified for most everything. Many parts probably have a very wide range of torque that is adequate for safe use. I don't think that it is even expected by the manufacturer to use them for everything.

Will the end all to this be that we start using a torque wrench for everything and then still find us in court because we didn't get the wrench re-calibrated every six to twelve months? Will it go to the extreme of having to document what torque wrench was used to torque what bolt/nut.

AndreyT

Now they should repeat the same test with torgue wrenches. I'm sure the results and their distribution won't be much different.

HillRider

Often followed by gebroken.

Sal Bandini

But then you get to use your bolt extractor and other ez out tools you bought and never use and then get to break those as well.

pdlamb

Probably no difference on the high side, but a torque wrench should reduce under-torqueing.


I've heard of a study the local calibration lab did on fasteners tightened with torque wrenches. Interestingly enough, those tightened by skilled mechanics with a beam-type wrench were the closest to the specified values. Less skilled (ahem) and skilled mechanics had reproducible results with the click type torque wrench -- they almost always came in high. Apparently when the torque wrench "broke" the landing on the next pawl overtightened the fastener to the next highest click torque level. That was reproducible with every operator and almost every fastener.

DrIsotope

Mechanics (IME) are the absolute worst at this, because they have to work on everything. I work on three bikes. The carbon always gets the torque wrench. The steel and aluminum get "feel" because they're more forgiving and the bolts don't move around due to flex. All I know for sure is that carbon is annoying-- definitely not a "set it and forget it" situation. The bike only gets the torque wrench, and I have to re-torque things like stem and seatpost binder bolts weekly at least.

Crankycrank

^^^Yeah, the beam wrenches tend to stay calibrated longer and tolerate more abuse. Not as convenient to use but generally less expensive and if you only occasionally have to torque something would be the best choice IMO. As mentioned already, many of the cheaper clicker torque wrenches that find their way into a cyclists tool box can be off by quite a bit when new and continue to get worse with use.

SquidPuppet

Kersnapen.

Iride01 

Good point about the material differences. I'd be more likely to worry about torque on aluminum and carbon frames because over-torquing the material can be more disastrous.

I've also wondered about the torque on things such as carbon frames and seat posts that are actually built to be truly light. Not the cheap ones that are carbon just to get a sale from those that are "marketing" oriented and not "performance" oriented.

I thought I'd noticed some mechanics on professional teams seem to give a lot of attention to seat posts and wondered if the differnce between the torque to hold your seat post securely and not damage the carbon was such that it loosened over time. Therefore it needs to be checked regularly.

SquidPuppet

Thank you. I'm glad I read this. When using the torque wrench that I have (click), it has always "felt" like I was going a bit far.

ThermionicScott 

Pride, I guess? A torque wrench allows anyone who can fog a mirror to torque a square-taper crank correctly, so then the shop rats would have to find something else to feel superior about.

SquidPuppet

Seriously? That often? I don't have a CF bike or any CF components so I have no experience with that. Seems like that would be very annoying after a while.