Topic starter
Sent a bike of to carbon bike repair for a health check. One of the pieces of feedback was that the top of the steerer hadn’t been cut completely straight so the rim of the bung wasn’t sitting flush against it all the way round. Apparently over time this can cause additional stress and they’ve seen breakages as a result.
fair enough I thought, I did that steerer myself and it wasn’t particularly tidy tbh. But then I looked at a fork I’d had the lbs cut, and it’s not completely straight either.
Obviously carbon bike repair know what they are talking about so I suspect I’ll need to get it sorted with a file. But I’m genuinely surprised. It’s not as if the bung is being clamped up hard. Neither bike had any wobble in the headset so that wasn’t an issue.
Posted : 26/03/2024 12:51 pm
I always cut mine freehand, some are pretty much straight - but others a bit less so.
Am still alive.
But seriously, it's just to preload - so it's not a problem at all (unless it's so wonky that the top spacer is loose one side)
Posted : 26/03/2024 12:56 pm
It'll depend on the stem / fork combo - some forks require the bung to be in a specific place to prevent crush forces from the stem being directed into the steerer tube.
Posted : 26/03/2024 1:01 pm
I'd be more concerned about the friation caused if you took a file to it.
Posted : 26/03/2024 2:28 pm
Topic starter
We are talking mm here so won’t affect stem support. It’s near impossible to cut a carbon steerer 100% straight with a hack saw, even with a guide. So the question is do I file or leave alone
Posted : 26/03/2024 2:54 pm
I'm curious about this. Surely the lip in the bung is just to stop it falling down the steerer tube?
Worst case, as you tighten the bung down, it could pull the lip down applying more pressure. If that were the case, concentrating all of that in a single high spot could cause a issue.
I'd be tempted to ask for clarification if it were my bike. No need to challenge, just ask to be educated.
Posted : 26/03/2024 3:50 pm
Sent a bike of to carbon bike repair for a health check.
Talking of educating, why would you send a frame off for a health check? Had it been crashed?
Posted : 26/03/2024 4:14 pm
Topic starter
Creak coming from chainstay area. Their health check includes the entire frame and fork
Worst case, as you tighten the bung down, it could pull the lip down applying more pressure. If that were the case, concentrating all of that in a single high spot could cause a issue
That’s what I thought but if you tighten a bung it he top bit doesn’t pull down, it’s the wedge at the bottom that is pulled up surely?
I guess if you then tighten up the headset the lip may push down on the steerer, but that would involve a fair bit of cranking to cause damage I’d have thought
either way I’m not going to say they don’t know what they are on about, so I’ll be checking my other carbon steerers just to be sure
Posted : 26/03/2024 4:28 pm
Without seeing the bung, it's hard to know but if both are tapered, then the top will pull down slightly. We're not talking about large displacements
Posted : 26/03/2024 4:37 pm
Topic starter
Ah I see what you mean. The bung on this bike specifically has the lip and the sleeve all as one piece of metal, but I have other bungs with wedges at top and bottom with the metal. sleeve inbetween
Posted : 26/03/2024 5:06 pm
