Torque Wrench - Wasted Money?

[Dirtbreath]

Just bought a fancy (damn expensive) torque wrench. Now doing a search for the recommended torque settings I come across this. Any thoughts?

 

"I'm sorry to piss on peoples fires about accurate torque, but years ago even NASA agreed that you can only reach +-25% torque accuracy on threaded metal fasteners. Remember torque only measures resistance, not how tight the fastener actually is. Worst case scenarios are as high as +-50% accuracy range depending upon a combination of simple variables like moisture, thread lubrication, accuracy of the pitch etc.

So that extremely 'critical' 5Nm bolt on your stem could be anywhere from 2.5Nm to a whopping 7.5Nm even though you used a $500 torque wrench accurate to within 0.001Nm! While it's nice to know you are 'roughly' in the correct range which a torque wrench can cetainly help you get a 'feel' for, I wouldn't bother trying to make it a science. Common sense when looking at what types of force the fastener and its component(s) are likely to be subjected to when you tighten that bolt is almost just as important."

[MichaelH]

I'm waiting for JB's comment with ill-concealed anticipation! 

[Weekend_Warrior]

i ONCE used a torque wrench to tighten my cleats as per manufacturer and pulled the thread out of my shoes resulting in an unexpected trip to the shop to buy new shoes. 

 

I just use common sence and when it feels tight enough it usually is

[WillemT]

Couldn't agree more!!... I always say, when i've spent the amount of money that a wrench would cost me, on stuff that broke because it was tightened wrong then i'll go and buy a torque wrench!...

For the last four years the amount of stuff that broke is standing on R0.00. So i'm far from buying a torque wrench...

[stringbean]

 

I agree.Usually tighten things till i hear the first crack,and then back off half a turn.

stringbean2008-09-06 01:53:44

[Johan Bornman]

He he he.  I've been telling you guys this for ages. A good mechanic knows what a certain torque feels like and combines his judgement of strength, the length of the lever and his common sense to come to an agreeable tightness for a particular bolt in a particular substrate. 175mm crank and can feel

 

Anyway, in order to get to a reasonably accurate tightness (irrespective of what torque the spanner reads out), you have to stick to lubricated bolts. The threads must be lubricated and, the underside of the bolt head too.

 

When torquing old style square taper cranks, the crank spindle has to be lubricated too.  Campag always told its customers to keep the spindle dry but that's wrong. The only known condition is lubed. It is very difficult to remove oil from something like a steel spindle since a one-melecule-thick layer (nearly) always remains.

[MichaelH]

See, I told you JB would not disappoint!!! 

[Dirtbreath]

Surely "feel" is affected by the same inconsistencies as a torque wrench? So if you are going to be inaccurate as you more than likely are, you might as well do it the cheaper route?

[turtlek]

rather let it feel tight than let it break off in your hand Oiltrash and besides would you rather have something break from overtightening (manufactuers dont warrantee) or would you have it break and be able to get it replaced

 

 

 

what my message comes down to is if it feels tight then you dont have to turn it anymore

[dirtrider]

A torque wrench for a tricycle !!! What's next ? Dyno for ur bike or maybe a ring compressor ? Just for the hell of it , what do you people use these wrenches for on the bikes ?

[porky]

I cant see the need for it, we arnt talking aerospace tolerances and technology here, we are talking bicycles for heavens sake.!

 

Tighten up till it "feels" tight to you, thats it. !

 

When I was an appy, my journey man always said, hold the spanner in the middle and tighten the fastener down, not on the end which allows you to apply too much torque - its worked for me ever since.

 

[Christie]

I agree that an experienced mechanic can get by without a torque wrench, if he learns the feel of the right torque using one at some point. Anything that changes the dry friction of the thread will influence the torque - lube, dirt, loctite etc will all influence bolt force, for both torque wrench and hand tightening.

Unfortunately, some (most?) bike shops dont have torque wrenches, so how can mechanics learn the right feel?

 

Something else to ponder: Deda did some tests on the handlebars & stems of the pro teams they sponsor and found that most bars & stems were torqued incorrectly. The pro mechanics in the studydid not use torque wrenches. 

[JPW#]

 

 

I agree.Usually tighten things till i hear the first crack' date='and then back off half a turn.

[/quote']

 

now that's pretty funny! If you have carbon bits on your bike , one crack is one crack too many hehe

JPW#2008-09-06 11:53:19

[Speed Devil]

About 80% op force applied to tighten a bolt/nut is used to overcome friction caused by the object being tightend i.e. the bolt head on the washer, the shank of the bolt against the wall of the object being tightened (no bolt ever sits exactly in the middle of the hole) and the threads on each other.

So all torque readings will be a ballpark figure and will vary depending on whether a lubricant was used or not. Therefore an unlubricated bolt/nut will reach it's torque setting quicker due to more friction.

 

Christie a person can use a torque wrench for 10 years and and then oneday tighten a bolt with a normal spanner and never get the torque correct as a person cannot gauge torque correctly due to the friction element.

Tightening by hand is a matter of common sense and a bit of experience. A torque wrench won't teach you either of those.

I recently had an experience at a bike shop where they broke the head of a crankbolt off due to overtightening, but won't go into detail now until the matter has been resolved (or the lack thereof).

As far as I'm concerned anything under 20Nm does not need a torque wrench. It is a marketing gimmick and someone is making money from it. If a person is so technically challenged that they cant tighten a bolt/nut without stripping it then they should rather take their bike to their LBS and get their mechanic to do it....Oh wait I done that and they broke my bolt!!

Speed Devil2008-09-06 12:04:56

[Christie]

I've got a 4-20Nm and a larger 30-150Nm torque wrench. I always use them to tighten bolts, but some experience also applies, like with bottle cage bolts.

Imo it is easier to get the torque in the right ballpark with a torque wrench than without.

 

The Deda study I mentioned was done after the mechanics complained that the bars/stems they were supplied with were bad quality. Deda conducted an investigation in response, and found that the components were not performing well because the mechanics were not applying the correct torque. If protour mechanics can get it wrong without a torque wrench, chances are that a bikeshop without a torque wrench will get it wrong, too.  

[Johan Bornman]

 

Cut cut cut cut

 

So all torque readings will be a ballpark figure and will vary depending on whether a lubricant was used or not. Therefore an unlubricated bolt/nut will reach it's torque setting quicker due to more friction.

 

 

I am not sure what you mean by that. If you have a lubricated bolt and dry bolt' date=' both will have the same reading on the torque wrench but the shaft of the lubricated bolt will be under more strain than the shaft of the unlubricated bolt. In other words, the oiled bolt component will be tighter.

 

 

Tightening by hand is a matter of common sense and a bit of experience. A torque wrench won't teach you either of those.

 

My experience differs. When I teach people about torque, we use a torque wrench with the socket connector clamped in a vice. I then demonstrate the different feel when the lever is long and short. We go up and down in the range and very quickly people get a feel for what is 50 NM and what is 6NM. Like Christie says. Common sense comes to play when you do water bottle cages. Eventually you know what will break a bolt off and what not. By practiciing with a torque wrench you can also judge what torque you are applying.

 

Practice makes better.

 

 

 

I recently had an experience at a bike shop where they broke the head of a crankbolt off due to overtightening' date=' but won't go into detail now until the matter has been resolved (or the lack thereof).

 

[/quote']

 

It is simple. Someone raped that bolt and that someone needs either some training with a torque wrench or a smack against the left ear with a large torque wrench. Either way, a wrench is required.

 

It also disproves some of the old myths that you can crack a crank open by tightening it too much. You can't. The bolt breaks first.

 

Interesting on a square taper crank is that once torqued, the bolt soon becomes loose after some hard riding.  This is because the crank squirms from pedaling forces that change the pressure on the leading and trailing edges and it can only go one way - up. That's why the bolt feels loose. In fact, it didn't unscrew, the crank just moved away from it. That's what dust caps are for - to prevent these bolts from falling out under these circumstances.

 

 

 

As far as I'm concerned anything under 20Nm does not need a torque wrench. It is a marketing gimmick and someone is making money from it. If a person is so technically challenged that they cant tighten a bolt/nut without stripping it then they should rather take their bike to their LBS and get their mechanic to do it....Oh wait I done that and they broke my bolt!!

 

I agree. However, someone needs to train with a torque wrench in order to get a feel for what 20NM is like.