Author Topic: Alu Steerer Tube - Bung or Star Nut (Read 13172 times)

токамак · « **on:** 15 March, 2011, 04:58:24 pm »

Is there any good reason why I can't use a bung designed for carbon steerer tubes in an alu steerer tube? They're easier to fit and I can't imagine they'd be any less effective. I can understand why you wouldn't hammer a star nut into a carbon steerer!

frankly frankie · « **Reply #1 on:** 15 March, 2011, 05:06:50 pm »

No reason. The star nut is just a cheap'n'cheerful OEM thing - building yourself you'd always want something better.

токамак · « **Reply #2 on:** 15 March, 2011, 05:11:08 pm »

Thanks, exactly what I thought. I ordered a new carbon fork with alu steerer and also specified the fork manufacturers carbon fork bung. The supplier has decided to send me a generic star nut instead though, I'll keep it, but I still want want my bung!

[edit] Supplier has apologised and is now sending bung.

Hot Flatus · « **Reply #3 on:** 15 March, 2011, 05:28:38 pm »

Star nuts are fit and forget, bungs can be a pain in the arse depending on the design

Greenbank · « **Reply #4 on:** 15 March, 2011, 06:02:54 pm »

There are different bung designs for carbon steerers and alu steerers.

You definitely shouldn't use a bung designed for an alu steerer in a carbon steerer, but I'm not sure about the other way round. It may be fine or it may just slip annoyingly over time.

rafletcher · « **Reply #5 on:** 15 March, 2011, 07:33:07 pm »

Chicken do a variety of bungs (for carbon) and expanders (for alu). They also do star nuts. The nuts are £2.99. The bungs/expanders run from £7.99 to £19.99. The cheapest expander specifically for alu appears to be £11.99.

Chicken Cycles

Tewdric · « **Reply #6 on:** 15 March, 2011, 07:39:04 pm »

Quote from: rafletcher on 15 March, 2011, 07:33:07 pm

Chicken do a variety of bungs (for carbon) and expanders (for alu). They also do star nuts. The nuts are £2.99. The bungs/expanders run from £7.99 to £19.99. The cheapest expander specifically for alu appears to be £11.99.

Chicken Cycles

Wholesale only though innit. Any decent LBS will hold stock.

PH · « **Reply #7 on:** 15 March, 2011, 08:35:47 pm »

Quote from: Greenbank on 15 March, 2011, 06:02:54 pm

It may be fine or it may just slip annoyingly over time.

My understanding is that once the stem is tightened the star nut or bung isn't doing anything at all. If that's right I can't see how it would manage to annoy anyone

Steve Kish · « **Reply #8 on:** 15 March, 2011, 09:25:08 pm »

Quote

My understanding is that once the stem is tightened the star nut or bung isn't doing anything at all.

Whilst they both act as an anchor point to tighten the top cup, a bung also acts as an internal anti-crush device to prevent carbon steerers cracking from tightening the stem.

Bung in alloy sounds like a good idea, as some of the star nuts seem to rust quite easily and are tricky to remove without a drill.

frankly frankie · « **Reply #9 on:** 15 March, 2011, 10:29:55 pm »

Quote from: PH on 15 March, 2011, 08:35:47 pm

My understanding is that once the stem is tightened the star nut or bung isn't doing anything at all.

+1

Biggsy · « **Reply #10 on:** 15 March, 2011, 10:44:29 pm »

The annoying slipping problem happens when you're trying to get it tight in the first place. This may happen with a bung, or even a start nut, if it's the wrong diameter or a poor design, or poorly fitted. It may get worse or better after repeated attempts. I think this is what Greenbank was getting at.

Greenbank · « **Reply #11 on:** 15 March, 2011, 11:52:10 pm »

A bung designed to grip against carbon may not grip as well against alloy. Certainly the images I can find of examples of both show they have quite different designs, so using one designed for a carbon steerer in an alloy steerer may be sub optimal.

gene hunt · « **Reply #12 on:** 15 March, 2011, 11:53:52 pm »

I always use a star nut on alloy / steel steerers, bungs always seem to slip to me.

токамак · « **Reply #13 on:** 16 March, 2011, 09:33:06 am »

Quote from: rafletcher on 15 March, 2011, 07:33:07 pm

Chicken do a variety of bungs (for carbon) and expanders (for alu). They also do star nuts. The nuts are £2.99. The bungs/expanders run from £7.99 to £19.99. The cheapest expander specifically for alu appears to be £11.99.

Chicken Cycles

It's actually the Columbus bung shown here

that I was intending to use in a Columbus fork - the Tusk Air Chrono shown here (scroll down).

I was thinking that the rubber rings and large surface area would reduce the chances of slipage? Also, where I've had problems with internal tube diameters and generic bungs not fitting in the past, I thought a bung and fork from the same manufacturer should be a good fit. Although I do appreciate that a Columbus carbon steerer might have a different internal diameter to their alu steerers. These things are never straightforward! I'm going to try the bung. I'll let you know how I get on.

токамак · « **Reply #14 on:** 04 April, 2011, 03:26:29 pm »

Update: all went together without issue. I did need to re-tighten it over the weekend though, on the second outing - I was getting knocking noises! Remains to be seen whether it's going to need constant attention, or if this was just some shake down adjustment...

Biggsy · « **Reply #15 on:** 04 April, 2011, 04:09:07 pm »

It may be some settling, but probably the stem isn't tight enough on the steerer if play is developing in the headset (allowing knocking noises). As mentioned above, the bung isn't doing anything, besides covering the hole, once the stem bolts are done up.

токамак · « **Reply #16 on:** 06 October, 2011, 04:30:09 pm »

Right, after almost 9 months and about 1500 miles (in TT bike) I'd say that on reflection it would have been better to bang the star-fangled thing in at the start and then forget about it. Although the bung has worked, it has needed regular repositioning and tightening due to slippage inside the alu steerer tube. I know that in theory the stem should hold the front together when tightened in place, but in reality, once the bung had slipped, a small amount of play started to develop through the headset.

I'm about to build a winter training bike with carbon fork / alu steerer - I'll be using the star nut on this one.

tiermat · « **Reply #17 on:** 06 October, 2011, 04:33:42 pm »

Quote from: токамак on 06 October, 2011, 04:30:09 pm

Right, after almost 9 months and about 1500 miles (in TT bike) I'd say that on reflection it would have been better to bang the star-fangled thing in at the start and then forget about it. Although the bung has worked, it has needed regular repositioning and tightening due to slippage inside the alu steerer tube. I know that in theory the stem should hold the front together when tightened in place, but in reality, once the bung had slipped, a small amount of play started to develop through the headset.

I'm about to build a winter training bike with carbon fork / alu steerer - I'll be using the star nut on this one.

My finding on the Ridley, near enough. After the last service I fitted (badly) a Thorn accesory bar, and didn't tighten up the top cap bolt up enough. Things worked loose which causednasty shimmy when braking at $FAST speeds....

Rhys W · « **Reply #18 on:** 06 October, 2011, 05:15:36 pm »

Quote from: CLINT on 15 March, 2011, 05:28:38 pm

Star nuts are fit and forget...

Yes, but if you ever need to get one out (not that I have, yet), you're screwed.

Can anybody explain the difference in a bung for carbon and an expander for aluminium?

Biggsy · « **Reply #19 on:** 06 October, 2011, 05:46:36 pm »

Quote from: Rhys W on 06 October, 2011, 05:15:36 pm

Yes, but if you ever need to get one out (not that I have, yet), you're screwed.

No, you just punch them down and through the hole in the bottom, or just least leave them in. They never actually need removing. Just a few grams of dead weight at worst. Just fit a new one on top. Regard them as fit-once devices.

Quote

Can anybody explain the difference in a bung for carbon and an expander for aluminium?

There won't necessarily be any difference, though the ones designed specifically for carbon should prevent scratching and may have a larger surface area, or may be more rubbery to grip better. Carbon needs more caution than metal, and is more slippery. Remember that even seemingly smooth metal is quite rough on a microscopic level.

I generally find bungs easier and nicer to deal with, though used a star nut instead once to save weight. Don't use star nuts in carbon.

Domestique · « **Reply #20 on:** 06 October, 2011, 05:53:50 pm »

I would go with a starnut, then again I have the tool for inserting starnuts

Imho bungs just do not look up to the job, but I have never used one so what do I know $:-\$

Biggsy · « **Reply #21 on:** 06 October, 2011, 05:56:48 pm »

Gotta use the tool now you've got it.

Actually I've bought quite a few tools that I've hardly or never used. T+1 is always good.

Seriously, a bung works well as long as it's a good design and the right size.

Hot Flatus · « **Reply #22 on:** 06 October, 2011, 06:06:28 pm »

I didn't realise there are different bungs for alloy and carbon. I've always fitted star nuts in alloy and bungs in carbon.

Biggsy · « **Reply #23 on:** 06 October, 2011, 06:26:43 pm »

It's not always clear what a particular bung has been designed for (partly due to crap descriptions from retailers), but you can make your own decision. Especially watch out for sharp edges.

frankly frankie · « **Reply #24 on:** 06 October, 2011, 06:35:08 pm »

Quote from: токамак on 06 October, 2011, 04:30:09 pm

I know that in theory the stem should hold the front together when tightened in place, ...

The stem has to hold everything together - nothing else is going to do it! (Top caps are nowhere near strong enough.)