# Rule of thumb torque conversions



## womble (Sep 8, 2006)

Off memory, Zinn's book used to have a very rough rule of thumb table for converting torque values to how tight your cranked down on a bolt as he acknowledged that most people wouldn't bother with a torque wrench. 

I've lost my copy of the book and rather suspect that the table wouldn't be included these days anyway because of liability reasons.

So, does anyone have a link for something like this? I've Googled and can't find anything. The old table was something like "x NM is just finger tight, use on shifters and brake levers.... y NM is as hard as you can tighten, use on bottom brackets".

I realise that going by feel is not at all accurate, but I'm not going to bother with a torque wrench unless I ever go with carbon parts (not in the forseeable future).


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## Cayenne_Pepa (Dec 18, 2007)

I've used snug+quarter/half turn with great results....


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## Brockwan (Aug 6, 2013)

I do use a t wrench but I would and have used same as above. Gives roughly 6nm

Sent from my iPhone using Tapatalk


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## Cleared2land (Aug 31, 2012)

Use your own judgment, but I've seen more than one destroyed set of aluminum threads that would have appreciated a torque wrench. I invest too much into my bikes to consider not using one.


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## WaveDude (Jan 14, 2004)




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## Mr Pig (Jun 25, 2008)

I've got three torque wrenches but the problem I have is that I do not trust them on the low torque values applied to most of the fasteners on a bike. 

With just an Allan key or spanner in your hand you get an excellent feel for force you're applying. Obviously, this has to be married to experience but a torque wrench removes or greatly blunts that feel so you are left having to trust the tool completely. I have stopped using my torque wrenches on the low-torque fasteners because I do not think that they are accurate enough at low values. On big bolts they work fine but a stem or brake clamp is something I would much rather do by hand.


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## Cleared2land (Aug 31, 2012)

Mr Pig said:


> the problem I have is that I do not trust them on the low torque values applied to most of the fasteners on a bike.


Interesting that I have the same feeling regarding the accuracy of low-torque values on a torque wrench. Has anyone used the Ritchey 5nm Torque Key for the low value torques? I'm thinkin' about getting one of these.


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## customfab (Jun 8, 2008)

The Bontrager or CDI units have much better handles. The Bontrager version is almost identical the Ritchey. The CDI is a completely different mechanism and I like it better, but it's more money. 

Torque wrenches shouldn't be trusted in the bottom 10% of their torque range. Most brands specifically call this out. The accuracy just isn't there on the bottom end of the scale. However some brands build just omit that 10%, so check with the owners manual that came with your tool. If you can't completely trust a tool you're either using it incorrectly, outside it's intended capacity or you just bought a pile of crap.


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## Mr Pig (Jun 25, 2008)

Cleared2land said:


> Has anyone used the Ritchey 5nm Torque Key for the low value torques?


No, but it looks like it works on the same principal as the Evans drum torque key








Which sorta works but the same sorts of issues remain. If there is more or less friction in the fastener in question the tension will be different from the others. It puts you in the ball park but is far from perfect.

The problem is that, on a bike, it's the low-torque fasteners you want to get right. You have a fair bit of leeway on things like crank bolts but it's easy to strip out small bolts threaded into aluminium. And when the required torque is low things like thread friction have a disproportionate effect on how much torque is actually required to achieve the desired tightness.

With an Allan key you get the feel of how the bolt is going in and how it is biting. With a torque wrench it is very easy to tighten that bolt way past where it should be if the wrench does not work properly.

It's like satnav syndrome. People want technology to relieve them of the burden of having to learn something and think for themselves. They would rather trust the tool, without considering how accurate the tool might or might not be.

I should clarify that I don't hate all torque wrenches! Wouldn't be without one for the car. It's just that on a bike I think that in most cases you're better learning the correct feel for the fasteners yourself.


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## shupack (Nov 28, 2012)

Cleared2land said:


> Interesting that I have the same feeling regarding the accuracy of low-torque values on a torque wrench. Has anyone used the Ritchey 5nm Torque Key for the low value torques? I'm thinkin' about getting one of these.


That's because you probably SHOULDN'T trust them. (or both..)

When I was in the Navy, TW's were NOT calibrated below the bottom quarter or above the top 1/8th. So if the torque spec wasn't between 25% and 87.5% of the wrench's range, you got a different one. I still use that thumb-rule.

I assume you have a std mechanic's 0-100 or 0-250ft-lb torque-wrench? 5inlb is way below the 25% mark on either of those, if you purchase a TW with the correct range, it will be just fine with the low torque values specified on most bicycle fastners.


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## yzedf (Apr 22, 2014)

Snug and a bump. Check things regularly. You'll find the three or four bolts that will need snugging that you don't want to Loctite.


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## Cleared2land (Aug 31, 2012)

shupack said:


> That's because you probably SHOULDN'T trust them. (or both..)
> 
> I assume you have a std mechanic's 0-100 or 0-250ft-lb torque-wrench? 5inlb is way below the 25% mark on either of those, if you purchase a TW with the correct range, it will be just fine with the low torque values specified on most bicycle fastners.


100 or 250 ft-lbs is automotive and tractor tool values. I have a 1/4" drive, 30-200 inch-lbs. (not ft-lbs) Snap On torque wrench.

I don't know of any fasteners that only use 5 in. lbs torques. Perhaps you're thinking 5 N-m as is commonly found on bikes. 5 N-m = 44.25 In-lbs.


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## shupack (Nov 28, 2012)

Cleared2land said:


> 100 or 250 ft-lbs is automotive and tractor tool values.


yes, that's what I was referring to.



> I have a 1/4" drive, 30-200 inch-lbs. (not ft-lbs) Snap On torque wrench.
> 
> I don't know of any fasteners that only use 5 in. lbs torques. Perhaps you're thinking 5 N-m as is commonly found on bikes. 5 N-m = 44.25 In-lbs.


Yes, typo (well, more like brain-fart...) 5 N-m.

44.25inlbs is below the 25% thumbrule value for a 0-200inlb even. , Ideally you'd want a 0-100inlb wrench to put it in the middle of the wrench's range.



> Snug and a bump. Check things regularly. You'll find the three or four bolts that will need snugging that you don't want to Loctite.


If bolts are coming loose during a ride, you need to give more of a "bump", they should not loosen up on their own.


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## kickhorse (Aug 3, 2013)

There was an old saying on the vintage motorcycle forums - "Tighten slowly until you strip it, then back it off a quarter turn..."

Seriously though, I'll use a torque wrench at first but after a few times on the same component I can usually just go by feel, especially on a bicycle. For moto or auto engine stuff, I'll reach for the t-wrench.


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## tooclosetosee (Aug 2, 2011)

I've got that ritchey torque wrench posted above and it is great for going around and making sure everything looks good before a race. It may be off what it says by a little bit, but it is going to be closer than me. Plus I think the only thing that couldn't take at least 5NM on my bike are the magura aluminum shroud bolts that are like 2NM. Those I am very careful with.


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## Mr Pig (Jun 25, 2008)

tooclosetosee said:


> It may be off what it says by a little bit, but it is going to be closer than me.


Yeah, fair enough. These things are ball-park at least and if you snug most fasteners a little over what the dial says they should take it no problem and you're still safer than using a long Allan key plus ignorance! ;0)

It's more the physically large wrenches that worry me on small bolts as it's very easy to apply much more force than intended without realising it.


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## Matty F (Sep 25, 2011)

While I do use a torque wrench daily, I try to calibrate my wrist to my most used set of allen keys (Park AWS-10 folding set) so that I can be reasonably accurate for the 95% of stuff which I don't think really merits a torque spec that is accurate to within 0.5Nm.

With the Park allen key lined up parallel with the body of the tool (unfolded 180°, rather than 90° which I only use to really reef on things):
- 6Nm is pretty much as tight as I can get a bolt before my hand slips around the tool.
- 5Nm is a pretty firm twist.
- 4/4.5Nm is snug

With the allen key bent to 90° for higher torque stuff:
- 12-14Nm (left Hollowtech crank arms) is about as tight as I can get it.
- 9-10Nm (chainring bolts, shock eyelet bolts) is a firm twist without straining myself.

I try to check my "calibration" every couple weeks just to make sure I'm not getting any weaker/stronger, or just plain veering off path.


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