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Discussion Starter · #1 ·
Quick Question:

Had to tighten up my headset the other day. Pulled the stem and I was surprised to find there were scratches on the steer tube mostly I assume from assembly and deburring. However what started to concern me was that the stem had left a ring mark / scratch almost completely around the steer tube where the stem clamp ends, in addition there were a couple vertical marks where it pinches as well. Is this common with full carbon forks? Shop built-up, bike is new, expander plug in stem, used torque wrench to reinstall at 5Nm Just kind of has me worried.

Replacement fork is $400.00. I have 30mm of spacers below the stem and it is flipped down. I could always remove the spacers, and flip the stem to get back to about the same position.

Thoughts??
 

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Discussion Starter · #3 · (Edited)
Don't think it's cracked. It's just hard to tell. No jagged edges or fibers showing. Hopefully if it was cracked it would be apparent. I could always pull it off and check it in the industrial xray here at work.

The carbon fiber has an odd almost luminescence when you look at it with a flashlight at different angles. I don't think the steer tube has the decorative weave layer on it. It's the top layer of matte epoxy or whatever that is marked up.

How tough are these steer tubes. I have never worked with carbon fiber so it is tough for me to gage the strength of the material.
 

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I have a carbon fork with a carbon steerer, and it's about 15,000 miles on this fork. I have had one major crash (I hit a car going about over 20 mph, right into its back bumper), about four minor crashes, etc. No trouble with the carbon steerer. For a well-made all-carbon fork (including the steerer) to be this sturdy is pretty common. My training partners have broken three carbon forks with an aluminum (i.e., alloy) steerer right at the stem or above the headset. They were sort of expensive forks, but overall, carbon forks with alloy steerers are more likely to fail that a fork with a carbon steerer.

The scoring has to be cosmetic. You can take your bike to a knowledgeable LBS and get them to look at your carbon steerer, if you're worried.
 

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chamois creme addict
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Try this out

Dave Hickey said:
It's a lot tougher than people think...carbon is extremely strong
I agree, carbon is very strong. As a test, take a piece of carbon steerer left over after cutting down a fork. Put a stem on it, with no expander plug or support inside the steerer, and then crank down on the stem bolts. It takes some SERIOUS torque to crack the steerer, if the stem threads do not strip first! Another way to do this "test" is to put a cut piece of steerer in a vise and crank down.

Carbon is strong, but it does not like point loading or point impacts. That is why a carbon steerer fares well with circumferential stress, but when someone crashes on carbon and the seat stay is rammed by another rider's wheel the stay ruptures.
 

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I also wouldn't be one to worry about that, but "lifetime warranty" may be made much shorter lived if your fork fails while riding at high speeds :)

The warranty covers the fork & frame, not your own body... And that's one part which does not have a price :)
 

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Unsafe at Any Speed
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My carbon steerer has developed similar wear marks. I think it is nothing to worry about : it will take a deep wear mark to start stress concentration cracks.

BUT : watch it. Loosen, inspect and retorque regularly (I do it monthly).

And : I have also seen wear due to the headset top bearing expander ring.

I think many of these components are made with scant respect for the carbon tube they ride on. I have smoothed the edges of my headset top bearing expander ring using 400 grit sandpaper. It was very sharp - nearly cut my finger. Ditto, carefully clean up the inside edges of the handlebar stem where it abuts the steerer.

These handlebar stems (the ones I have seen) are really unsympathetic. The horizontal tube should be closed where it stops against the steerer. But it's not. It is an open cylinder with thin walls and often sharp edges. Really ! At the prices that these simple things command, why can't they be closed to present a full sleeve to the surface of the steerer? Or will that mean losing 5 grams to the competition??

Anyway, do your fork a favour. If at all possible, move the thinnest spacer to above the stem. This means the full width of the top edge of that horizontal stem cylinder will clamp the steerer. If a steerer is cut so that there is a slight clearance between its end and the stem's upper face (as it has to be), the stem loses out on seating area in crucial way when the stem is fitted as high as it can go. (IMO at least).
 
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