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I guess it all depends how accurate Superstar torque wrenches are.
Having tightened my stems bolts to the numbers recommended on here (2.5 I think) I could still easily move my bars.
So I tightened the bolts until it "felt right", which has served me well all the time we've had aheadsets . The bars weren't abe to be moved.
On checking the torque with my wrench it said 10nm.
The recommended torque settings barely nipped the bolts up.
If I hadn't asked for the correct numbers I'd be happily riding around . Carbon steerers are a new thing to me so just checking.
Which will kill me first loose bars or snapped steerer?
2.5NM seems very low to me. My carbon road bike's carbon stem is 6NM on all bolts and, oddly, my Thomson alloy stem on my MTB is 4NM on the bar interface and 5NM on the steerer. I'm less fussy about this stem, so I suspect they're pinched up a bit tighter than this. I'd be more concerned about stripping threads than crushing a carbon steerer as the load you put through by tightening it should be even across the surface and facing to the centre of the steerer.
This discussion has been had before, but I'd use carbon anti-seize on the interface with the bar, but not on the steerer interface if you can avoid it as it can seep down into the headset bearings and cause premature wear.
tl;dr: I'd be much less concerned about over torquing a stem/steerer interface than I would about the bloody thing coming loose mid-ride! 🙂
Loose bars without a doubt!
Anyway, the bung offers support against crushing - I assume that's why they are so long so they fully support the clamp area.
2.5 is not far off finger tight I'd say. Most of my stems say 6-9 I think which is still not very tight but seems to work ok.
For a carbon steerer I just make sure I have a head-doctor type thing that's a snug fit, so it supports the stem torque. What are you using in there? Not even sure what it's called, the thing that replaces the SFN.
As above, 2.5Nm does seem ridiculously low. I think I remember seeing some fasteners where that was the specified torque, but they were M3 or smaller.
5 to 10 would be the range I would expect for an M5 bolt, possibly even more for a larger bolt.
I did have one stem rotate a bit after I'd set the bolts to 5Nm (I think) and then had to make adjustments on the trail as my bars weren't quite straight, I tried to get them back to the same position but I think they were a touch under. I cleaned everything up and put some grip paste on/tightened to the 6Nm max torque on this stem, and it seems to have worked.
Whether it's aluminium or carbon you're clamping, it's worth taking care to get everything clean before assembly as the last thing you want is to be scoring the steerer with a bit of grit every time the stem moves.
Also, make sure you don't get the grip paste in the bearings of course 🙂
For a carbon steerer I just make sure I have a head-doctor type thing that’s a snug fit, so it supports the stem torque
Yeah, this too.
Although as a bit of an experiment I took an old stem and a bit of excess carbon steerer and tightened the stem as far as I dared, with no damage to the steerer. Obviously it wasn't being bent as well, but I suspect people worry a bit too much about this - it seems far more likely that a loose headset leading to scoring (carbon will wear away very quickly in the wrong conditions) and/or manufacturing defect would be the root cause of a steerer failure.
My stems on carbon steerers are set to what it says on the stem, typically 5Nm.
That's with either a Ritchey Torque Key or a X-Tools Torque Wrench, funnily enough a 4mm allen key tightened to a slight bend / spring in it is pretty much the same too.
The 2.5 figure might be wrong but the 10 is certainly right.
Fork has one of those carbon bungs in . I shall now ride happy.
I have never seen a stem clamp as low as 2.5NM, normal range would be 4-6NM, some as high as 9NM. Some stems recommended torque may exceed the fork manufacturers max clamp.
I normally use 5NM as a go to, but check first.