OP
OP
Smokin Joe
Squire
- Location
- Bare headed cyclist, Smoker
Why?
BTW, what I meant was the top of the (Long) expander sleeve is about 9mm below the top of the steerer.
Torque For Carbon Steerer?
- Thread starter Smokin Joe
- Start date
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BTW, what I meant was the top of the (Long) expander sleeve is about 9mm below the top of the steerer.
Yellow Saddle
Guru
- Location
- Loch side.
My head is spinning, so let me give my take on this.
1) A naked, unprotected carbon steerer that is LOWER than the stem can be squashed by the stem by the clamping force of the stem and repetitive strain.
2) Either protect the steerer with a suitable full tubular aluminium insert that will counter the clamping force or have it protrude above the stem and take up the necessary space with a spacer that leaves enough space for adjustment.
3) Do not use a fangled nut on carbon but always an expander.
4) The expander, if sensibly designed or judiciously positioned and properly tensioned, can protect a steerer that's shorter than the stem.
There are many ways to skin this cat but in the interest of self preservation, skin him good. Cervelo's approach is to cut the steerer shorter like we did in the days of aluminium, but glue a steel (alu?) sleeve inside the steerer to prevent crushing. This is combined with a fangled nut but only because the fangled nut now bites into metal, not carbon.
Spoked Wheels
Legendary Member
- Location
- Bournemouth
Do you mean the top of the expander is 9mm below the top of the 10 mm spacer?
The top of the bung should be flashed on top of the steerer tube, remember that it serves as a star nut. I visualise this as 1mm above your stem and then the 10mm spacer sitting on the stem, leaving you with 9mm between the top of the spacer and the top the bung.I guess that would be ok.
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OP
OP
Smokin Joe
Squire
- Location
- Bare headed cyclist, Smoker
Right, I haven't really explained this very well.
1/ Check. The top of the stem is below the top of the steerer.
2/ Check. I have a 10mm spacer above the stem taking up the slack.
3/ Check. I am using a bung (With a long expander sleeve) and not a star nut.
4/ On a recheck the top of the expander sleeve sits about 6mm below the top of the steerer.
5/ I've got a headache.
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Spoked Wheels
Legendary Member
- Location
- Bournemouth
I'm sorry and I don't mean to be disrespectful but did you copy and paste the above text?
Yellow Saddle
Guru
- Location
- Loch side.
No, I never copy someone else's work without due acknowledgement. Those are my thoughts distilled from my experience.
Yellow Saddle
Guru
- Location
- Loch side.
Take an asprin and go for a ride. Your vitals are fine.
Spoked Wheels
Legendary Member
- Location
- Bournemouth
I didn't think they weren't your thoughts but maybe something you wrote before. The reason why I thought so was that you started going on about start nuts (forget what you call them
) when it was pretty clear we were talking about a bung.
OP
OP
Smokin Joe
Squire
- Location
- Bare headed cyclist, Smoker
From memory, didn't the early Boardmans come with a star nut in the carbon steerer?
Yellow Saddle
Guru
- Location
- Loch side.
Most of the early bikes would have been like that. The assumption was that because it looks the same, it works the same.
Nowadays the manufacturers have various methods of preventing steerer collapse, but that too, went through some evolution.
The first, as you say, was a start nut.
Then we had the first expanders, which were shallow and generally couldn't be installed so that it protects right up to the upper edge.
Then we had expanders with extended lead-out tubes and flanges on top which encourages the user to install it all the way in.
Specialized (and perhaps others) now produce an explander with a lead-out tube that's as deep as the stem is high.
Cervelo still uses a star nut but modified the system. After cutting the steerer to size (as with old aluminium steerers which were cut to below the stem), you glue in an aluminium sleeve. Inside this you bang in a star nut.
Some stem manufacturers approached the problem of steerer squash by cutting the pinch clamp diagonally.
I've seen stems with three bolts and a long clamp.
At first these problems were attributed to poor stem torqueing but if you look at the problem and how a stem clamps and how it is manipulated during hard riding, the problem is obvious.
Somewhere in my archive of failure photos I took over the years, I have a photo of a squashed Cervelo steerer. I remember the case well, it was my first. The customer complained about a creaking handlebar, he didn't even notice the movement in the stem. Looking from the top and head-on with the tube's section, the crack looked like a round ridge running down into the steerer. If you looked under good light, you could see the ridge comprised of loose fibres which were separated from their matrix.
I'm searching for the photo but I have thousands, most never renamed but simply named DCMYZ.jpg. That doesn't help the search.
migrantwing
Veteran
As @Yellow Saddle has mentioned, I do similar. Carbon steerer protrudes a few mm higher than the stem, 5mm spacer on top of the stem so that the stem tightens onto ALL of the steerer. The few mm above and the spacer save the steerer from being crushed.
Spoked Wheels
Legendary Member
- Location
- Bournemouth
Thinking about it carefully, the important thing here is not to let the headset cap rest on the steerer tube. If it did then you wouldn't get the effect that is required from a bung + top cap combination which is to compress the whole steering system together. It the steerer was higher than the stem then the headset cap would definitely rest on the steerer tube, hence the need for a spacer that sits on to stem.
The other bit where I think one has to be careful with is the area where the stem clamps the steerer tube. If the bung is long enough then fantastic, most stems are about 40mm tall but I've seen one or 2 50mm tall, my expander (bung) is 48mm long so the stem clamps on an area of the carbon fibre steerer that is supported by the expander inside the steerer tube. However, if the expander is one of the short type then there might be a chance that the stem would clamp on an area of the steerer that is unsupported by the expander. My guess is that people have done their sums correctly and assuming you don't have the steerer protruding above the stem, the expander would be tall enough.
The 48mm expanders aren't just a Specialised thing, I bought one from either CRC or Wiggle I think.
