Torque number questions

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Mtek
Posts: 107
Joined: Tue Jun 13, 2017 4:27 pm

by Mtek

Hello, searched and couldn't find info, thought I'd ask here.

Does the material for torque matter, is it a universal number regardless if the bolt is steel, ti, aluminum, etc? Example: Torque Nm for steel stem bolt is 5.5, so Ti would be 5.5 as well?

I know this may seem irrelevant, but I'm curious as to the answer anyway.

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kkibbler
Posts: 813
Joined: Tue Sep 09, 2014 9:30 am

by kkibbler

Torque is a universal measure regardless of material

by Weenie


MRM
Posts: 309
Joined: Sun Jun 14, 2015 8:15 pm

by MRM

Also you don't want to go right to that value, but rather remain about 10% below.

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bura
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Location: Civitatis Vaticanae

by bura

Not sure if kkibblers post answers OP's question. :noidea:
I am sure that the fastening torque for different kind of steel bolts of the same size is different ,too. As it is different if a bolt is lubed,plated etc. So I would not automatically torque the bolts of the same part with the same figure when changing to an other bolt material,rather then try to figure out what kind of Ti(or other material) the bolt is made from if no manufacturer specs available for a correct torque application.
Considering that the material of the bolts are changing and not the material of the stem.
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Mtek
Posts: 107
Joined: Tue Jun 13, 2017 4:27 pm

by Mtek

Thanks all, I plan to use 10% below list.

I thought the torque ratings are to guide and limit how much a bolt will stretch, and how the number can affect diff materials. I don't think it is a huge diff, but it's always nice to know what's going on.

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Hellgate
Posts: 98
Joined: Mon Mar 27, 2017 8:49 pm

by Hellgate

No, use the specified number, that's why the number was specified. 10% could lead to a part coming loose. Ti bolts behave like steel one and work very well. Just make sure you use some anti seize so they don't gall. Damn galls... Aluminum bolts are typically for show and don't last.

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kkibbler
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Joined: Tue Sep 09, 2014 9:30 am

by kkibbler

As you tighten a bolt, greater and greater torque is required because the increasing tension in the bolt increases the friction within the thread interface. A material that "stretches" more than another will require less torque to reach a certain number of turns, or in other words, will require more turns to reach the same amount of tension than a bolt material that stretches less, but ultimately both require roughly the same amount of torque to reach the same amount of tension, regardless of number of turns needed to get there. On the extreme end of the spectrum, a bolt made of cheese will be incredibly stretchy, and you can turn it forever and not reach 5nm. By the same token you'll never crush a seatpost by tightening a bolt made of cheese.

EDIT: assuming similar coefficient of friction between materials.

Greasing a bolt is different because you're reducing the friction within the thread interface without affecting the "stretchiness" of the bolt itself.

@Hellgate, it depends. Sometimes the specified number is a target, other times it's a limit. Best read the label on a part.

by Weenie


Mtek
Posts: 107
Joined: Tue Jun 13, 2017 4:27 pm

by Mtek

@kkibbler

Your explanation was exactly what I was asking about. Ridiculous example with cheese, but it's perfect and got the point through lol. Thank you.

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