Originally Posted by
Brian Ratliff
So, what's the torque spec for a carbon bar? Surely it can't be the number written on the stem, right? Unless the stem and the bar are a matched set, there is no way the stem manufacturer knows what bar you are mating it to. I've never seen a torque spec matched to a handlebar.
Also, the torque specs written next to bolts are MAX specifications, not minimums or "numbers to shoot for". Basically, if you go over the specified torque, you might damage the screw threads and no-this-is-not-a-valid-warranty-claim.
From what I remember, 6 or 7 Nm. It comes with the bar instruction, in my experience.
The clamp on a stem doesn't close entirely up on itself. There should always be a space between the faceplate and the stem.
To achieve the clamping pressure on the bar requires a certain torque spec on the bolts, and it's not to avoid stripping the thread. If you exceed the torque spec, you are pulling the face plate of the stem into the bar tubing, and hence bringing into play a crush force which then breaks the epoxy resin and either displaces or breaks the carbon threads underneath.
There was a celebrated case on the Road Forum last year when a poster detailed how he heard a crushing sound on the CF bar he was installing, and the torque on the faceplate bolts was much less than the spec. And he was using IIRC, a small hand torque wrench designed for doing this work.