Only 5Nm on a stem/handlebar clamp?

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Manc33
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Only 5Nm on a stem/handlebar clamp?

Postby Manc33 » 14 Nov 2019, 1:00am

Found this best selling China carbon handlebar, more than 1,000 people have bought one of these, it's dirt cheap (about £14).

It says "5Nm" on the stem clamp :shock:

Image

So I take this to mean if you have 4 bolts on your stem as a lot of stems do, you should only clamp each bolt at 1.25Nm for a total of 5Nm?

Are they having a laugh?

My stem says 5Nm per bolt on it, giving a total clamp force of 20Nm - which is what I would guess is needed to hold a component like this on, safely. Surely they can't mean 5Nm per bolt.
When two cyclists get married, they should throw anodized cable crimps instead of confetti.

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robgul
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Re: Only 5Nm on a stem/handlebar clamp?

Postby robgul » 14 Nov 2019, 7:25am

Not sure how you get to think the torque is divided by the number of bolts (a crankset would then be 6-7nm per bolt rather than 12-14nm!)

It's per bolt .... 1.25nm is not a lot more than finger tight. IIRC the nm for a crank set plug is about 0.7nm which finger tight.

Doubtless someone will be along to argue but I'll keep all my stem bolts at the normal 5-6nm

Rob

Brucey
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Re: Only 5Nm on a stem/handlebar clamp?

Postby Brucey » 14 Nov 2019, 7:35am

Manc33 wrote: ….So I take this to mean if you have 4 bolts on your stem as a lot of stems do, you should only clamp each bolt at 1.25Nm for a total of 5Nm?....


why would you think that?
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pwa
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Re: Only 5Nm on a stem/handlebar clamp?

Postby pwa » 14 Nov 2019, 7:40am

5Nm for each bolt, and all done up evenly. That is about standard I think.

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Mick F
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Re: Only 5Nm on a stem/handlebar clamp?

Postby Mick F » 14 Nov 2019, 8:39am

I use an Allen key and tighten the bolts.
So long as they are nice and tight and the handle bars can't move, that'll do me.
Mick F. Cornwall

Valbrona
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Re: Only 5Nm on a stem/handlebar clamp?

Postby Valbrona » 14 Nov 2019, 8:39am

5Nm per bolt, and carbon paste.

And don't do your lever clamps up too tight as well.
I should coco.

pwa
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Re: Only 5Nm on a stem/handlebar clamp?

Postby pwa » 14 Nov 2019, 8:43am

5Nm isn't much and doing it with an allen key is risky. I broke a stem where it clamps on the steerer by overdoing it and I was trying to be moderate.

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Mick F
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Re: Only 5Nm on a stem/handlebar clamp?

Postby Mick F » 14 Nov 2019, 8:50am

I'm nowhere near having them so tight that I break anything.
I reckon the threads would strip way before anything broke.
Mick F. Cornwall

reohn2
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Re: Only 5Nm on a stem/handlebar clamp?

Postby reohn2 » 14 Nov 2019, 8:52am

Brucey wrote:
Manc33 wrote: ….So I take this to mean if you have 4 bolts on your stem as a lot of stems do, you should only clamp each bolt at 1.25Nm for a total of 5Nm?....


why would you think that?

Why indeed! :?
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Brucey
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Re: Only 5Nm on a stem/handlebar clamp?

Postby Brucey » 14 Nov 2019, 9:07am

Mick F wrote:I'm nowhere near having them so tight that I break anything.
I reckon the threads would strip way before anything broke.


FWIW with modern faceplates having 4xM5 bolts, common failures are

a) that thin walled metal handlebars are visibly crushed/deformed and/or
b) that the face plate itself cracks near one of the bolt holes.

I'm not saying it can't happen but I don't remember seeing a stripped thread in a very long time.

FWIW there is a significant underlying concern here, which is that there is often a potential conflict between the clamping recommendations for a stem and a handlebar, especially if they come from different makers. Some stems generate clamping loads that are not favourably distributed for some handlebars. I would suggest the prudent course is

a) not to mix stems and bars from different makers if it is possible and/or
b) defer to whichever is the lower torque/clamping setting.

cheers
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reohn2
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Re: Only 5Nm on a stem/handlebar clamp?

Postby reohn2 » 14 Nov 2019, 9:11am

And 'soften' any sharp arris/corners on clamping parts of the stem with fine grade emery or similar.
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pwa
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Re: Only 5Nm on a stem/handlebar clamp?

Postby pwa » 14 Nov 2019, 9:18am

Mick F wrote:I'm nowhere near having them so tight that I break anything.
I reckon the threads would strip way before anything broke.

No. With some modern clamps the castings are so thin that you can snap them long before you get near thread stripping. Which is a fault in the design as far as I am concerned.

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Mick F
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Re: Only 5Nm on a stem/handlebar clamp?

Postby Mick F » 14 Nov 2019, 9:21am

I never give it a second thought.
Tighten it. That's all.
I do the same with every single bolt, screw and fastening. Always have done and never a problem.

On Mercian, I have a quill stem.
Cinelli 1R with a single Allen bolt underneath that tightens a wedge against the 'bars.
I've been using it and the handle bars since 1986 and it needs to be very tight. Maybe it's crushed the Cinelli 64 'bars a bit, but I don't know or care. Never had them out or adjusted them in decades.

The Moulton came with an adjustable A head stem. I've since bought a fixed one and new 'bars too. I swapped out the original four bolts and fitted nicer SS ones. I tighten them with an Allen key nice and tight.
Recently had the 'bars out to fit new 'bar tape. No problems or issues with the 'bars. They are back in now and nice and tight.
Mick F. Cornwall

Brucey
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Re: Only 5Nm on a stem/handlebar clamp?

Postby Brucey » 14 Nov 2019, 9:27am

some people's version of 'nice and tight' leaves handlebars tight enough and doesn't cause damage. Not everyone can say that, or is prepared to take the risk of not using a torque wrench on critical parts like these.

cheers
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pwa
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Re: Only 5Nm on a stem/handlebar clamp?

Postby pwa » 14 Nov 2019, 9:33am

Mick F wrote:I never give it a second thought.
Tighten it. That's all.
I do the same with every single bolt, screw and fastening. Always have done and never a problem.

On Mercian, I have a quill stem.
Cinelli 1R with a single Allen bolt underneath that tightens a wedge against the 'bars.
I've been using it and the handle bars since 1986 and it needs to be very tight. Maybe it's crushed the Cinelli 64 'bars a bit, but I don't know or care. Never had them out or adjusted them in decades.

The Moulton came with an adjustable A head stem. I've since bought a fixed one and new 'bars too. I swapped out the original four bolts and fitted nicer SS ones. I tighten them with an Allen key nice and tight.
Recently had the 'bars out to fit new 'bar tape. No problems or issues with the 'bars. They are back in now and nice and tight.

You are safe with the quill stem and older style bars. But with the Ahead stuff I'd be a bit more cautious. Some of it is underbuilt. Maybe your stem and bars are made with a bit of common sense robustness, but not all are. I snapped a stem when I tightened a bolt on a steerer, and I was using two fingers and a thumb with moderate force. So I started using a torque wrench for that and found that 5Nm isn't much at all. Very easily exceeded with an allen key in your hand.