Which torque recommendation?

Discuss light weight issues concerning road bikes & parts.
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drainyoo
Posts: 736
Joined: Sun Jun 17, 2007 6:56 pm

by drainyoo

When clamping parts together with different torque recommendation, which do you use? For example, clamping a stem to a bar. Stem has a torque recco of 4nm and the bars has 5nm. Which do you go with?

by Weenie


kode54
Posts: 1125
Joined: Tue May 23, 2006 9:39 pm

by kode54

i always use carbon paste...and in your case, i would go with the lower only when using the paste for assembly.
- AX Lightness Vial EVO D + DA9150 + Enve SES 3.4 carbon hubs
- Parlee Altum + DA9150 + Enve SES 4.5 carbon hubs
- Parlee ESX + DA9150 + THM SRM PM + Enve SES 6.7 CK hubs
- Independent Fabrication Ti FLW + DA9100 + Enve 3.4 CK hubs

Jepas
Posts: 69
Joined: Wed Feb 22, 2012 6:56 pm

by Jepas

You should always use the lowest value, otherwise you may damage the "weakest link" of the assembly.

youngs_modulus
Posts: 512
Joined: Wed Sep 20, 2006 1:03 am
Location: Madison, WI USA

by youngs_modulus

A torque specification for a handlebar is nonsensical; a bar has no threaded parts.

I wrote a little post a few years ago answering this question in detail:

viewtopic.php?f=3&t=66911&start=5

If you're in tl;dr mode: use carbon paste on the bar/clamp interface, thoroughly grease the stem bolts and tighten them to the stem spec of 4 N-m. Remember to snug the bolts against the clamp until they're finger tight and then apply those 4 N-m in sequence and slowly. In other words, turn each clamp bolt roughly one turn at a time, alternating in an X-shaped pattern.

Cheers,

Jason

drainyoo
Posts: 736
Joined: Sun Jun 17, 2007 6:56 pm

by drainyoo

Thanks folks. My example was made up, but in the manual for my Zipp SL bars it does indicate a max torque for it. I've also seen other carbon parts without threaded parts to have torque limits. That's what I was asking about. But it was answered. I will use the lower number. Thanks.

youngs_modulus
Posts: 512
Joined: Wed Sep 20, 2006 1:03 am
Location: Madison, WI USA

by youngs_modulus

drainyoo wrote:in the manual for my Zipp SL bars it does indicate a max torque for it. I've also seen other carbon parts without threaded parts to have torque limits.


<Jobst>

Specifying a torque value for a non-threaded part hints strongly at incompetent engineering. (Or, more charitably, a moment of extreme engineering sloppiness).

A torque value is meaningless without thread pitch. This is equivalent to specifying a maximum speed in meters. In both cases, the value is means nothing on its own and more information is required.

</Jobst>

I'm glad you found the information you needed. While using the lower torque value, I'd still check very carefully to ensure that all parts are secure. At best, a handlebar that slips while riding is irritating. At worst, it causes a crash.

Cheers,

Jason

drainyoo
Posts: 736
Joined: Sun Jun 17, 2007 6:56 pm

by drainyoo

Thanks Jason. Got it. So using carbon paste essentially let's you apply less torque to the bolts and still get a secure grip?

youngs_modulus
Posts: 512
Joined: Wed Sep 20, 2006 1:03 am
Location: Madison, WI USA

by youngs_modulus

Yes; carbon assembly paste inhibits slipping. I'd use it on bar/stem and seatpost/frame interfaces if slipping was a problem without it.

For what it's worth, carbon paste is essentially grease with very fine sand in it. Theoretically, you could easily make your own.

Cheers,

Jason

drainyoo
Posts: 736
Joined: Sun Jun 17, 2007 6:56 pm

by drainyoo

Awesome. Thanks.

by Weenie


em3
Posts: 887
Joined: Tue Dec 23, 2008 2:57 pm
Location: NYC

by em3

Do not confuse MAX torque with recommended torque...two very different specs. This topic has been covered comprehensively on this forum in several previous threads. EM3
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