Should we torque bolts to their max spec'd torque when greased

Discuss light weight issues concerning road bikes & parts.
biwa
Posts: 175
Joined: Fri Sep 21, 2018 8:39 pm

by biwa

I grease almost all the bolts on my (rim brake) bikes, and wonder how/if doing so affects the proper amount of torque one should apply. What's the proven approach among mechanics?

TobinHatesYou
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Joined: Mon Jul 24, 2017 12:02 pm

by TobinHatesYou

biwa wrote:
Sun Nov 10, 2019 2:28 am
I grease almost all the bolts on my (rim brake) bikes, and wonder how/if doing so affects the proper amount of torque one should apply. What's the proven approach among mechanics?

Grease any bolts unless explicitly instructed otherwise. Also make sure the bore and bolts are clean with no grit/dirt in the threads.

by Weenie


spartacus
Posts: 115
Joined: Mon Apr 04, 2011 6:53 pm

by spartacus

I wouldn't recommend torquing things to their max spec in general and if you grease it, it will get tighter with the same torque so that's risky.

DaveS
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Joined: Fri Mar 24, 2006 1:26 pm

by DaveS

Max torque values should not cause a problem whether the threads are lubed or not. I use anti-sieze, not grease.

That said, if you can't tighten a stem or seatpost clamp without a torque wrench, you shouldn't be working on bikes.

The only items I use a torque wrench on are threaded bottom brackets, cassette lockrings and ultra-torque joining bolts.

biwa
Posts: 175
Joined: Fri Sep 21, 2018 8:39 pm

by biwa

TobinHatesYou wrote:
Sun Nov 10, 2019 2:38 am
biwa wrote:
Sun Nov 10, 2019 2:28 am
I grease almost all the bolts on my (rim brake) bikes, and wonder how/if doing so affects the proper amount of torque one should apply. What's the proven approach among mechanics?
Grease any bolts unless explicitly instructed otherwise. Also make sure the bore and bolts are clean with no grit/dirt in the threads.
And how much torque should we apply?

spartacus
Posts: 115
Joined: Mon Apr 04, 2011 6:53 pm

by spartacus

DaveS wrote:
Sun Nov 10, 2019 3:19 am
Max torque values should not cause a problem whether the threads are lubed or not. I use anti-sieze, not grease.

That said, if you can't tighten a stem or seatpost clamp without a torque wrench, you shouldn't be working on bikes.

The only items I use a torque wrench on are threaded bottom brackets, cassette lockrings and ultra-torque joining bolts.
My friend that worked at a bike shop (background we are both mechanical engineers) and I got into a throw down argument at a bar. Both our girlfriends were mad. He says you should just torque stuff to the rated amount. I told him he's an idiot. He goes and cracks the steerer tube on the fork of his allez sprint torquing it to spec. Not sure who is right but he could have just tightened it until it didn't slip and not ruined the fork IMO.

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Dilbert
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Location: South Africa

by Dilbert

Lubricant will reduce friction in the thread and under the bolt head. This results in higher preload force in the bolt, and correspondingly more stress. The manufacturer should allow a margin of safety when specifying the torque (I mostly torque to the value specified by the manufacturer, but sometimes torque lower on risky areas, like bottle cage bolts)

Clean, dry mating parts with a bit of Loktite 243 is my preference.
Last edited by Dilbert on Sun Nov 10, 2019 6:28 am, edited 1 time in total.

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Alexbn921
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by Alexbn921

DaveS wrote:
Sun Nov 10, 2019 3:19 am
Max torque values should not cause a problem whether the threads are lubed or not. I use anti-sieze, not grease.

That said, if you can't tighten a stem or seatpost clamp without a torque wrench, you shouldn't be working on bikes.

The only items I use a torque wrench on are threaded bottom brackets, cassette lockrings and ultra-torque joining bolts.
You don’t work with carbon parts or titanium bolts if you think monkey tight is good enough.

Most torque specs are for a dry bolt. If you use grease or some other lubricant than it’s a safe bet to slightly reduce you applied torque. For things like carbon bars or seat posts where over tightening will destroy the part, I tend to error on the lower side.

Every bolt on a bike should be torqued to factory spec with the proper surface treatment applied. Great mechanics can get close, but have the tools to do it right.

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nickf
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by nickf

At the shop I always use a torque wrench or torque key. I don't grease stem bolts, seatpost binders. Dry, clean bolts, and threads.

For things like crank bolts, rear derailleurs, bottle cage bolts, pedal threads, yes I use grease because that's what's recommended.

If I brought my bike to a shop and they tightened my bars by "feel" I would find another shop. I don't care about experience. Your tightening a critical component and it takes no extra time to properly torque it down.

DaveS
Posts: 2721
Joined: Fri Mar 24, 2006 1:26 pm

by DaveS

Assembling with dry threads is an invitation for broken bolts or stripped threads, when it comes time to remove the bolts, particularly with dissimilar metals. If both threads are stainless or Ti, then anti-sieze is a must.

I've been wrenching on carbon fiber bikes for over 25 years. I'm a mechanical engineer. Never using a torque wrench on seat post clamps or stems, I've never broken any part or had slippage problems. I can make adjustments to my bars or saddle out on the road without fear of damaging something. No torque wrench needed.

FWIW, zipp stems come with lubricated threads and have the same 5Nm torque rating as nearly every stem on the market.

If your M5 Ti bolts are close to breaking with 5Nm of torque, you have crappy bolts. I've done tests with stainless steel M5 bolts and nuts to see how much torque it takes to break one. I was able to break some with 15Nm. As another test, I used a long handled 4mm hex wrench and applied all the pressure I could on the same type of stainless M5 bolt and couldn't break it. If bolts are threaded into an aluminum mating part, those threads should strip before a bolt breaks.

Try the same sort of test with a cheap 1/4 inch or M6 steel bolt and it will break easily.
Last edited by DaveS on Sun Nov 10, 2019 4:56 pm, edited 1 time in total.

Jugi
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Joined: Sun Jun 24, 2018 8:10 am

by Jugi

I don't install dry bolts. Grease or a locking compound always.

"Max torque" value is exactly that - a maximum recommended value of torque, not the recommended torque. It should have a safety margin in it, because as a recommendation it has to be safe for use. However at the same time, that is the maximum recommended value, and ending up slightly below should be plenty tight.

Also, a correctly tightened joint should have enough give to act as a "fuse" in an accident or similar extremely high load situation. For an example a stem shouldn't have any give at either end during normal use, but it is beneficial for those joints to give away before snapping a handlebar or a fork steerer in an accident.

DaveS
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Joined: Fri Mar 24, 2006 1:26 pm

by DaveS

Jugi wrote:
Sun Nov 10, 2019 3:18 pm
I don't install dry bolts. Grease or a locking compound always.

"Max torque" value is exactly that - a maximum recommended value of torque, not the recommended torque. It should have a safety margin in it, because as a recommendation it has to be safe for use. However at the same time, that is the maximum recommended value, and ending up slightly below should be plenty tight.

Also, a correctly tightened joint should have enough give to act as a "fuse" in an accident or similar extremely high load situation. For an example a stem shouldn't have any give at either end during normal use, but it is beneficial for those joints to give away before snapping a handlebar or a fork steerer in an accident.
Total nonsense. The four bolts holding the bars to the stem or the two holding the stem to the steerer will never fail before the bars or steerer break.

Max torque means do not exceed this value. 5 is fine, 6 is not.

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Kayrehn
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by Kayrehn

Given that 3.5nm is the recommended torque for many ww bars and stems, 5nm is probably more than enough for most cases.

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Jugi
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by Jugi

DaveS wrote: Total nonsense. The four bolts holding the bars to the stem or the two holding the stem to the steerer will never fail before the bars or steerer break.
Did I hit a language barrier?

Let me give you an example of what I meant: I have hit a pothole in the dark so hard, my cyclocross bike's handlebars rotated at the stem joint. Stem bolts were torqued evenly to allowed spec, carbon paste had been used as recommended for the carbon handlebar etc. All components survived and once at home base, I adjusted the bars back to position.

by Weenie


DaveS
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Joined: Fri Mar 24, 2006 1:26 pm

by DaveS

Jugi wrote:
Sun Nov 10, 2019 4:35 pm
DaveS wrote: Total nonsense. The four bolts holding the bars to the stem or the two holding the stem to the steerer will never fail before the bars or steerer break.
Did I hit a language barrier?

Let me give you an example of what I meant: I have hit a pothole in the dark so hard, my cyclocross bike's handlebars rotated at the stem joint. Stem bolts were torqued evenly to allowed spec, carbon paste had been used as recommended for the carbon handlebar etc. All components survived and once at home base, I adjusted the bars back to position.
That makes more sense. It's common for the stem or bars to rotate out of position in a wreck, but if that ever happens to me, I carry the hex keys so I can realign the bars immediately and not have to ride home with crooked bars. I don't need a torque wrench for minor adjustments.

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