I've had two road frames and forks set up by the manufacturer with SFNs in carbon steerers (a Boardman and a Cannondale Six13).
I want to put one in my current fork - a Kinesis - because the expander bung i'm using at the moment (made by Profile) works loose when i really give it some in a sprint. I have no confidence in it whatsoever.
Is it really *that* bad an idea to put an SFN in a carbon steerer? If it is, can anyone recommend a truly reliable expander bung?
Thanks.
The expander bung shouldnt be doing anything after preloading and tightening stem bolts?
FWIW I have an FSA expander in my PX carbon forks. It works OK, although Its not great at preloading IMO.
What he said - you need to clean up the steerer/stem and grease the bolts - though it's possible the bung, if undersized, isn't supporting the steerer enough and that's whay it's slipping.
SFN - no way, will damage the carbon.
BTW what kind of sprinting are you doing? Points in road races?...or trying to catch the puffing fatty who's just passed you on the Apollo? 
Hmm, maybe i need to clamp the stem up tighter. If anything though i probably over-torque it (don't have a torque wrench) and i do use carbon paste as well.
Cynic-al - i'm not doing any road races this season but town sign sprints on club runs are very important
Yep do your stem up properly (use some carbon assembly paste perhaps) and it won't spin, it's more scary you're relying on your top cap to hold your front end together...
SFN, bad idea.
Edit: too slow. You must be doing sommat wrong though, I imagine Cav is a better sprinter than yourself (no offence meant), and he doesn't seem to have problems...
Stoner is correct. The expanding bung should be taking no load in day-to-day use, it is for pre-loading the headset only. The problem lies in the clamping of your stem to your steerer tube. On a carbon steerer the torque on the stem bolts is important as over-tightening can cause steerer ovalisation which can actually cause a less secure connection.
SFN's are a bad idea in carbon steerer tubes. I'd go as far as to say the Boardman and Cannondale where incorrectly set up.
I work as a bicycle mechanic. That however, doesn't mean I am always correct 
As a first step I suggest buying a torque wrench or taking the bike to a shop that has one. Also worth considering is the stem clamp type and design, plus the area being clamped on the steerer tube - what gap is there between the underneath of the preload cap and the top of the steerer. Can you reduce this with a thinner headset spacer?
Njee20 - actually i did just have a quick Google search for what pros use but i didn't find anything.
I'll clean everything up and try again. I have a suspicion it may be that the Profile bung is so rubbish it leaves a little bit of slack in the preload from the start. I've got minimal spacers on the steerer already.
Thanks for the advice all.
I've had problems with expander plugs coming loose over time, but recently started using the PRO version, which is working very well. MTB and Road bikes, no problems.
It also happens to be a good chunk lighter! Bonus 
This one mtbmatt?
That's the one.
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