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Thread: Torque Specs?

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    Junior Member gallo4343's Avatar
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    Torque Specs?

    Interested in buying a torque wrench to make sure I'm not over- or under-tightening the bolts on my LeMond Big Sky S. The Park Tool description of their torque wrench says that bike manufacturers will have specifications for the amount of torque on each bike. Is there only information for certain manufacturers? I know LeMond's we presence is pretty weak, but does that mean they won't have any information?

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    The bike manufacturer's don't publish torque specs but the component makers do. There are tables of recommended torque values for various components on bikes. Here is a spreadsheet Lennard Zinn published: http://www.velonews.com/media/torque.xls

    Note that stem manufacturer's recommended torque values for the steerer and handlebar bolts are probably too high if you are using them on carbon components.

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    Park's website has specs for the complete Shimano line plus a bunch of other specific common components by other manufacturers. It's in the how-to for torque wrenches. The tech docs for your components typically have specs also.

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    Quote Originally Posted by HillRider View Post
    The bike manufacturer's don't publish torque specs but the component makers do. There are tables of recommended torque values for various components on bikes. Here is a spreadsheet Lennard Zinn published: http://www.velonews.com/media/torque.xls

    Note that stem manufacturer's recommended torque values for the steerer and handlebar bolts are probably too high if you are using them on carbon components.
    This is a good point. If you're at all concerned about torque, you should check the specs of all the components involved. Usually the torque spec is for the fastener (i.e. bolt), but when you look at things like a carbon seat post, it's often the seat post that gives you a torque spec as opposed to the binder bolt.

    For stems there's two other parts you need to check with - the fork steer tube and the handlebar. Your stem will have a spec for tightening, but the handlebar or fork might also have, and it might be less. If it's more, you gotta stick with the smaller of the two because if you over torque a bolt you can not only jeopardize the bolt itself, but also the structure that the bolt is tightening into. More often they (the handlebar and fork) will state something like: refer to stem torque specs.

    Just FWIW as I've recently learned about the wild world of carbon parts and accompanying paranoia.

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    Senior Member johnknappcc's Avatar
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    I would probably go for another brand, craftsman or such, to save yourself some money. If you are getting a deflector style (like the Park) you can find them for cheaper. Nothing against Park, but 40 dollars for 3/8 deflector style torque wrench seems a little pricey.

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    Quote Originally Posted by Camilo View Post
    Just FWIW as I've recently learned about the wild world of carbon parts and accompanying paranoia.
    It isn't paranoia if they are really after you!

    Carbon steerers and handlebars are less forgiving than their metal predecessors so paying attention to the torque recommendations is a good way to keep the entire bike under you where it belongs.

    Having broken a handlebar clamp bolt on a steel stem no less and gone through the resulting crash (at very low speed fortunately) I have a healthy respect for doing it right. Four bolt faceplates torqued properly are your friends.

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    From my experience the torque specs found on stems do not protect carbon fiber steer tubes or handlebars. I recommend a maximum of 5 nm for carbon fiber parts, or less if specified.

    Al

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    Quote Originally Posted by Al1943 View Post
    From my experience the torque specs found on stems do not protect carbon fiber steer tubes or handlebars. I recommend a maximum of 5 nm for carbon fiber parts, or less if specified.

    Al
    Please, do expound.
    Mes compaingnons cui j'amoie et cui j'aim,... Me di, chanson.

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    Quote Originally Posted by operator View Post
    Please, do expound.
    The threadless stems I've seen typically have 8N-m torque recommendations engraved on both the steerer clamp and handlebar clamp bolts. I agree that is higher than I'd want to use on carbon steerers or handlebars.

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    I once did a test with a scrap piece of carbon steering tube and a stem having two large M6 clamp bolts. I tightened the bolts to a ridiculolusly high torque with a long handled hex wrench and it caused no damage whatsoever. I didn't use a torque wrench to get an exact torque value, but only an idiot would use a long handled wrench and pull as hard as he could to tighten a stem. That was the idea, to see if an idiot's approach to the job would crack the steering tube.

    I expect that most damaged parts are either poorly made or have a sloppy fit with the mating part, causing pinching and a stress concentration.

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    Quote Originally Posted by DaveSSS View Post
    I once did a test with a scrap piece of carbon steering tube and a stem having two large M6 clamp bolts. I tightened the bolts to a ridiculolusly high torque with a long handled hex wrench and it caused no damage whatsoever. I didn't use a torque wrench to get an exact torque value, but only an idiot would use a long handled wrench and pull as hard as he could to tighten a stem. That was the idea, to see if an idiot's approach to the job would crack the steering tube.

    I expect that most damaged parts are either poorly made or have a sloppy fit with the mating part, causing pinching and a stress concentration.
    I expect if you repeat the experiment using a removable face plate stem and a carbon handlebar, the outcome would be far different, even if the parts were well matched.

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    Quote Originally Posted by operator View Post
    Please, do expound.
    I'm sure you've heard this story before. A few years ago I broke a carbon fiber steer tube at 8 nm, the torque limit shown on the stem. The fork was $850.

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