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Stem/Fork/Handlebar Assembly and Torque
#1
Hi there,

I had my local bike shop install the headset on a new frame, and I'm trying to take over from there. I've got questions regarding properly attaching the stem to the steerer tube and the bars to the stem.

For the stem to the steerer tube, should the assembly be dry or lubed? It's a carbon steerer tube and an aluminum stem.

Same question for the bars and the stem, where the stem is aluminum (still <g>) and the bars are carbon.

Last question is about torque settings. I thought this was going to be easy, as the parts are marked, but now I've read that the numbers on the components might be maximums rather than recommended settings, or might be a total value. (As in 6nm is the max for each bolt. Or that 6nm is the force that should applied across both bolts to secure the assembly so 3nm each.)

Also the bars are marked like this:

torque:
10NM-M5
15NM-M6

What do the M5 and M6 mean? And are the two values the upper and lower end of a range?

The faceplate on the stem is marked at a much lower torque, which sort of gives credence to the idea that the 6nm on the stem is a max per bolt, and that if I tightened each of the 4 bolts to, say, 3nm I'd be between 10 and 15 ...

Thanks for the help,

Andrew
  Reply
#2
Andrew - some prefer a dry interface between carbon and metal but I prefer to use one of the lubes (Finish Line Fiber Grip for example) specifically made for that purpose. Annoying noises can arise from dry fits. Stay away from petro-based lubes as they can affect the clear coat on some carbon components in a bad way.

M5 and 6 refer to the size of the Metric Bolt. Torque specs are 'per bolt', not divided by the number of bolts. They are also generally a max recommended. Silly, huh? Thank the lawyers!
I usually stay 2 or 3 below that number with carbon unless it just doesn't "feel right".
Marked stems are usually done so for bars and steerer tubes from the same Mfr designed as a system. You're not likely to break the stem - it's the crushing of the carbon part that you need to worry about. Just be sure to tighten them each a small bit at a time like you would with lug nuts on a car wheel.
Wheelies don't pop themselves. (from a QBP fortune cookie)
  Reply
#3
Thanks for the tips, RobAR. I've already got it together dry, but will pick up some Fiber Grip if things start squeaking or slipping.
  Reply


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