[Closed] Split clamp stem on a carbon steerer?

I wasn't aware you needed anything different on a carbon steerer? I have a normal one on mine so would like to know too!

I’ve probably not being paying enough attention myself, but I believe you need to focus on how far the (star nut replacement) bung goes into the steerer in relation to the stem. If you are clamping on a part supported from behind by the bung then you’re good to go

It'll be fine if you have a spacer above the stem. It'll probably be fine if you don't but old school armchair engineering always said this 😀

I find split clamp stems like the style above move with less effort in a crash, so regardless of material I'd be running a spacer above the stem, even if it's small. It enables all of the stem to be in contact with the stem, rather than partially sitting above it.

If you are in doubt just buy a new stem, they are cheaper than new forks or teeth.

Make sure the bolts are greased so that you get an accurate torque reading when you tighten up the stem bolts.
As long as the stem is good quality with no burrs then I can't see the problem.

Make sure the bolts are greased so that you get an accurate torque reading when you tighten up the stem bolts.

Is that right? Greasing will result in a tighter clamping on the steerer for a given torque reading. Normally stem bolts have threadlock on them, although if you use liquid threadlock that would also have the same effect as grease. So more caution required if you grease.

You do not grease bolts and expect an accurate torque reading. Lightly wiped with light oil or use threadlock if worried about seizing. Greaseing them before using a torque wrench will lead to either a crushed steerer or overstressed bolt ( unless the torque value is quoted fro greased bolts.

I would want the bolts coppaslipped - another reason I do not use a torque wrench on a bicycle. Stem bolts are not critical for tightness - better too slack than too tight especially with a clamp onto CF

tjagain
Full Member

You do not grease bolts and expect an accurate torque reading.

Very much this

ime / from what I've seen, you're best not using minimally shaped stems on carbon steerers. Large internal front area cut-outs or open areas at the back reduce contact area. Pressure is force over area, you need a certain amount of grip to keep the stem in place and the problem with carbon is it's relatively soft and the stem is hard Al. I've seen steerers bulged or compressed by stems (by overtightening in almost all cases) and any compression is working that stem corner edge into the surface as it flexes. The more surface area and the more even the grip the better.

Personally I wouldn't use that stem on a carbon steerer. It may well be fine if you're careful and don't tighten it too much but there are better options.

You do not grease bolts and expect an accurate torque reading.

Strictly speaking the applied torque is as "accurate" (or not) as the tool/measuring device used, I think you mean clamping force, and yes you will typical achieve higher clamping forces when using a lubricant to reduce thread friction.

So if you lubricate the threads you will apply significantly more clamping force, theoretically it could be twice as much. And as Jameso points out concentrating that clamping force over a reduced area will ultimately mean more load going into the steerer.

If possible use a full clamp stem, try not to exceed the specified torque (5 Nm?), I'd suggest using the bolts as they come, if they have blue Loctite pre-applied fine, if not fit them dry to maximise thread friction. If you don't have a torque wrench, use the short end of a hex key to limit your mechanical advantage...

Thanks everyone, enough worry here that I think I'll look for something not so aggressively CNC'd