 You don't need to be an 'investor' to invest in Singletrack: 6 days left: 95% of target - Find out more
Hi Folks,
Building up a little town bike at the moment that has a carbon fork.
I have ~30mm of spacers under the stem and ~25mm of spacers above it.
I'm using a Deda carbon fork bung that is 70mm long so with the stem in its current position it is supported.
Ideally I would just cut the steerer but whilst I have a Park Tools steerer cutting guide I don't think its compatible with the wider saw blade that I also do not have ☹Â
Apart from the (questionable) aesthetics do any of you see an issue with this set up?
Probably ok....My only concern would be does the bottom of the bung go down into the bottom of the stem clamp? That would be something I'd be unhappy with. Maybe juggle the spacers so not quite so much above the stem. Was running a too short bung in mine and it never quite felt secure.Â
Now running a 70mm bung w 10mm spacer above and feels totally secure 
Â
Do any of you see an issue with this set up?
Depends on the steerer perhaps. A bung that's 70mm long may be designed to go down through (for ex) 5mm of spacer above the stem, 40mm of stem and 15mm of spacers with the lower edge staying below the bearing ring. If the bung is longer than the stem's 40mm or so and ends above the headset, one Q with that set up could be about a tensioned bung that is effectively rigid and moves with the stem. So it's a internal part that as it moves back-forth with bar & stem loads now puts stress on the inside edge of the steerer above where the steerer exits the headset. Some bungs have relatively sharp lower edges and many bungs work on expansion (carbon steerers flex under load as well as expand when a bung is tightened).
I don't know how that all works under cyclic loading, the flex will mean loads are concentrated somewhere. Maybe ok, maybe not - idk.
Bungs that go well below the level of the upper headset bearing compression ring seem like they'd provide good support. Also reminds me of the broom handle up the steerer thing with 70s road bikes.Â
Agree it depends on the bike
My giant came from factory with a bung that didn't even extend past the bottom stem bolt. Giant told me that was fine. Spesh on the other hand recalled all the tarmac sl7s as the original bung was too short and they were snapping, new longer bung was the fix
Personally I struggle to see how the bungs support the bottom clamp of a rigid carbon steerer, all the ones I've seen are very thin alloy way less strong than the carbon structure. Unless you are an ape with the torque wrench I think you'd be going some to crush a carbon steerer from a reputable brand
As above, id actually be more concerned about a bung extending beyond the stem but not the headset, for the reasons jameso stated.Â
Take my opinion with a pinch of salt mind you. I know nothing about carbon structures and what it takes to destroy them
Â
For the steerer cutter can you not just space the plate out with a 2mm washer - should give clearance for the carbon blade.
Does the bung need to go down that far? Isn't it just there to act as a star washer and provide preload for the head set?
Would have thought if a fork was to fail it would be at the bottom of the steerer tube.