Anyone crushed their carbon steerer tube?

kant314

I'm just wondering cos I've been fitting a new headset and I've noticed that the stem bolts that hold the stem onto the carbon steerer are done up to the max so that the stem has no more leeway to tighten.
Is this indicitive of having crushed my carbon steerer tubes, or more accurately, compressed it?
Do I need a new set of forks?

any advice appreciated,

thanks
Kant

maddog 2

did you do the bolts up?

kant314

stem bolts that hold the stem onto the carbon steerer are done up to the max

Monty Dog

Have you got a proper carbon fork compression bung fitted? If so, you'll be OK. BTW stem bolts don't normally need more than 8-10Nm, depending on bolt size / make - if more then something's not right - probably the stem is oversize

kant314

got a proper bung and the stem is right size.

maddog 2

well clearly it shouldn't happen like this so either:

a) you've tightened them up too much (which is what I was trying to gather earlier)

b) the stem is a little on the large side in terms of tolerances (fairly unlikely)

c) the carbon steerer is a little on the small side (as above)

or some combination of all three

Did you use a torque wrench?

Stem bolts should only be tight enough to hold the stem in place, yet allow the bars to turn if you give them a good hard yank. That way, in a crash the bars will turn rather than snapping your steerer. Same goes for brake levers and gear pods.

kant314

maddog 2 wrote:

well clearly it shouldn't happen like this so either:

a) you've tightened them up too much (which is what I was trying to gather earlier)

b) the stem is a little on the large side in terms of tolerances (fairly unlikely)

c) the carbon steerer is a little on the small side (as above)

or some combination of all three

Did you use a torque wrench?

Stem bolts should only be tight enough to hold the stem in place, yet allow the bars to turn if you give them a good hard yank. That way, in a crash the bars will turn rather than snapping your steerer. Same goes for brake levers and gear pods.

My question is , is it possible to tighten the the stem so much that it crushes or compresses the steerer tube so that it's effective diameter is smaller?

I fear I may have done this since my stem bolts do up all the way and there is no gap i.e no more that the stem can close or clamp round on the steerer tube.It's at it's limit.
The stem seems to be holding the steerer tube ok i.e. it's not loose, but I'm not sure about it's longevity.

No I don't have a torque wrench.

I'm just wondering if anyone has had any experince of this, but I guess not.

maddog 2

I suspect it is possible. I've overtightened bar end clamps on carbon bars in the past.

I'd be tempted to whip the stem off and have a look at the possible damage. You may have cracked the steerer tube.

If that were the case then it would be handy to know - the prospect of your bars coming off on a downhill would be pretty ugly. :shock:

kant314

thanks maddog.
Steerer looks ok, just a little compressed.

Pirahna

I've manage to crush one. Externally there was no sign of any damage but it had de-laminated on the inside. I'd recomend taking the fork bung out and checking the inside as well as the outside for any damage.

Garybee

kant314 wrote:

thanks maddog.
Steerer looks ok, just a little compressed.

If the stem has been done up too tight it won't have "compressed" the steerer tube, it may well of crushed or cracked it though. Carbon firbe doesn't have any plastic deformation so if it is forced into a new shape that it doesn't immediately return from it's wrecked i'm afraid.

SJLcp

If the steerer "looks a little compressed" then this is a euphemism for "its now knackered" and you should throw it away. I was at a friends house this w/e where he was showing me his Scott CR1 fork where exactly the same had happened, rather than crush and fracture, the carbon squashes into the shape of the steerer - this affects its integrity. My mate was a bit gutted since he then had to buy a new fork.

The allen key he had used to tighten the 3mm allen bolts on the steerer and it was very long (about 5") which encourage overtightening - these bolts only require a low torque to avoid crushing. I would also encourage using carbon antislip paste - this is also useful on the internal bung to avoid that pulling upwards when tightening the top cap.

I have managed to crush carbon bars when fitting bar ends and damage carbon seatpins and I must admit to thinking that for these items, is it really worth it? I would probably prefer the peace of mind of an alloy steerer or an allow s/pin next time and the knowledge that its impossible to break it?

kant314

If the steerer "looks a little compressed" then this is a euphemism for "its now knackered" and you should throw it away. I was at a friends house this w/e where he was showing me his Scott CR1 fork where exactly the same had happened, rather than crush and fracture, the carbon squashes into the shape of the steerer - this affects its integrity. My mate was a bit gutted since he then had to buy a new fork.

thanks for the info, guys.
I think I'm going to buy a set of forks with Alu steerer.
Wiggle do carbon forkswith alu steerer for £35 (ITM basic)
They weigh about the same as my ITM 4 Ever forks anyway.


cheers
Kant

aracer

SJLcp wrote:

I have managed to crush carbon bars when fitting bar ends and damage carbon seatpins and I must admit to thinking that for these items, is it really worth it? I would probably prefer the peace of mind of an alloy steerer or an allow s/pin next time and the knowledge that its impossible to break it?

A lot of carbon bars won't take bar ends (unless you use an internal plug to support them). Meanwhile most of these problems can be avoided by using a torque wrench - these parts are designed to work properly only as long as they are used properly (hence the disclaimer on many items about using a professional mechanic).

kant314

yeah, I'm pretty sure I must have overtightened the stem.
I presume it's not such an issue with alu steerers?

maddog 2

As said, the problem is overtightening, not carbon components per se.

SJLcp

Regards the bar ends, these were on a Ritchey WCR carbon bar which had alloy internal reinforcing rings - I ended up crushing one end because the bar end kept slipping and when tightened further it crushed the bar.

Whilst I agree with the comments on overtightening there is zero room for error.

adyshort

SJLcp wrote:

I would also encourage using carbon antislip paste - this is also useful on the internal bung to avoid that pulling upwards when tightening the top cap.

Any ideas where i can get this anti slip paste as my Wife's FELT has exactly this issue.

Cheers

Ady

Smokin Joe

adyshort wrote:

SJLcp wrote:

I would also encourage using carbon antislip paste - this is also useful on the internal bung to avoid that pulling upwards when tightening the top cap.

Any ideas where i can get this anti slip paste as my Wife's FELT has exactly this issue.

Cheers

Ady

Here -

http://www.probikekit.com/display.php?code=A0083

jpembroke

I've experienced this as well and it was due to the stem clamp not being lined up with the bung. Carbon steerers will deform under load so the bung needs to be the same length if not longer than the stem clamp and needs to be positioned in exactly the right place within the steerer so that the clamp is lined up with it when the stem is fitted. To be on the safe side it is worth getting a long bung with a shim to stop any compression of the steerer from happening. I have a Planet X supersafe bung, which comes with a couple of shims of different thicknesses. Seems to do the trick.

Also, has this stem been overtightened on an alloy steerer in the past? I've done this and caused the bolt holes to pinch together a bit i.e. they became bent out of shape. It may be worth trying a different stem as well.