Handlebar height and steerer tube expansion bung

[Xenopus]

I’m building up a track bike. I’m new to the track, and (at the age of 66) rather inflexible, so I want to experiment with handlebar height before I cut the steerer tube. This experimentation will involve clamping the stem on parts of the steerer tube that are not supported by the steerer tube expander bung. Is this safe, assuming that I don’t exceed the recommended torque of 5 Nm? As soon as I get the position right and the steerer tube cut I’ll set it up correctly, with stem and bung aligned.

in case it makes a difference, it’s a Condor Lavoro frame set.

Many thanks in advance. You can tell that I don’t have much experience in bike mechanics!

 

[Sharky]

The bung expander thingy is not there to support the stem clamping, so doesn't matter where it is relevant to the stem. The bung is to allow the stem to be pressed down to put tension on the headset bearings. Once the stem clamps have been tightened, the bung has no use and could be removed completely, but of course it should be kept in place for the next time you want to tighten the headset bearings.

It might be worth getting an adjustable stem to experiment more easily with different bar heights. Then get a stem with the required degree rise.

Herne Hill is a very large track so will be more like riding on the road. Haven't ridden at HH, but I did ride Bootle track once which was very similar.

Good luck

 

[Xenopus]

Thanks, Sharky. I should have mentioned that it's a carbon steerer tube, in case that makes any difference. I have seen others claim that the bung expander thingy is important both for pre-tensioning and for supporting the stem, but clearly the primary purpose is pre-tensioning and the support business may well be a bit post hoc. Anyway, I won't worry about it.

Good idea about the adjustable stem. I'm getting on a bit, and I'm not as flexible as I was!

Hope you're well and avoiding the Kent COVID variant!

 

[Sharky]

Hope you're well and avoiding the Kent COVID variant!

So far I have and I had my first jab last week.

Another thought, if you can replicate your road bike position. As long as you can hold the drop position for 10-15 mins it should be a good starting point.

If you have a front brake, riding a few 10 mile TT's on fixed would be good practice. If they ever start this year, you would be welcome at our Gravesend evening 10's down in Grain. A bit far for you to travel, but it's a nice course for fixed. That's what I ride.

Cheers

 

[Xenopus]

Thanks! Gravesend sounds like fun.

I am a volunteer vaccinator at the laboratory where I work, and I had my first Pfizer jab a month ago.

I had a bike fit last year and am using this as a first approximation, but was imagining that I might get lower down on the track than on the road. Reading all this, and seeing how much I have Googled, makes me realise that I do have a tendency to over-think these things!

 

[the snail]

The bung expander thingy is not there to support the stem clamping, so doesn't matter where it is relevant to the stem.

That's not necessarily true, or safe. You need to follow the manufacturer's instructions, and some will specify where the stem is vs. bung, how much steerer you can have, number of spacers above/below the stem etc.

 

[fossyant]

At least with a bung you can move it with the spacers. A star washer you can't. It's only really there to enable you to get pre-load on the bearings.

 

[boydj]

If it's a carbon steerer I'd be wary of having the stem not at least partly supported by the steerer bung. You should be able to get a longer screw to reach the bung from the top cap if you have to drop it a bit.

 

[coldash]

About 4 or 5 years ago a well known Italian bike brand had to recall the forks on some models because they had fitted a bung that was too short to support the steerer tube where the stem was clamped (there is a video somewhere of a rider on that brand crashing during a race when his steerer tube collapsed and the handlebars detached). They subsequently installed much longer bungs to ensure that there was sufficient support.

In additional there are two styles of bungs. The first have a lip that rests on the top of the steerer tube and the other can be placed more or less anywhere in the tube. In either case, the stem should be clamped over where the bung sits and it’s also a decent idea to make sure there are no burrs on the stem as these can dig into the steerer tube