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So I decided to travel with my bike this week and to my surprise discovered that the steerer is carbon fiber. I had removed the stem from the steerer for packing but naively assumed it was aluminum like my previous bike (both have carbon forks).

I would like to reassemble this so that:

  1. it doesn't come apart causing a horrible crash
  2. I don't want to crack/damage the steerer

I do have a torque wrench with me but not my copy of Zinn, so how tight should I clamp the two stem bolts? (they are labelled 10Nm but I think that's the rating for the stem, which is probably aluminum)

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What is a "steerer"? –  Daniel R Hicks Aug 7 '11 at 3:18
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@Daniel R Hicks: The "steerer" tube is the portion of the fork which runs from the fork crown, up through the bike's head set and head tube, and into the stem clamp. On quill stems, it is the portion which receives the quill and binding wedge, and on threadless systems it is the portion the stem clamps to. It sounds a little odd, perhaps, but it is correct terminology. –  zenbike Aug 7 '11 at 5:35
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3 Answers 3

Assuming the stem was chosen by the manufacturer, it's required torque as printed on the stem should be within the ability of the fork steerer to support.

If the stem says,"Max Torque 10Nm" as opposed to just "10Nm" then start with a lower setting around 6Nm and work up slowly until the stem clamp will not slip on the steerer. If only the number is printed, it must be exactly that number.

It is a good idea to check the torque compatibility of parts purchased for your bike. If you buy a stem that requires 12Nm, but your handlebar won't support more than 10Nm, you are destined for trouble.

Usually, 6-8Nm is enough for that purpose. You can lower the required torque by adding a carbon friction compound, sometimes called carbon grease. It increases the friction between the steerer and the stem clamp and will therefore require less clamping force to stay solid.

I assume you've dealt with this issue long since, but in this case 10Nm would be correct.

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You were right first time - the labelling on stem is the max torque that the bolts and stem are rated to withstand. Carbon steerer tubes are typically rated significantly less, and easily crack through crushing by 8Nm. I tighten mine to 4.2Nm, Specialized rates a max 5Nm for their forks. Additionally, the use of a thin layer of carbon grease / carbon friction compound between the stem and the steerer tube can help you ensure that at even low Nm you get a solid grip.

Carbon parts, wrenching at home - make sure you know the torque ratings everywhere.

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Unfortunately, you will probably have to contact the fork manufacturer. I am sure that each brand has their own ratings.

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