Is it safe to ride on carbon fork with scratch
- Thread starter mamil
- Start date
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midlandsgrimpeur
Well-Known Member
It is very hard to tell from a pic, but the third photo down does look like a compression mark (perhaps made by the stem, as per Webbo's comment).
Rub your finger over it, if it is a compression mark you will quite clearly feel some indentation in the carbon. If it is a scratch, the tube surface will feel flat/level as normal, you will just feel a small abrasion from the scratch.
If it is compression, then it is time for a new fork.
Rub your finger over it, if it is a compression mark you will quite clearly feel some indentation in the carbon. If it is a scratch, the tube surface will feel flat/level as normal, you will just feel a small abrasion from the scratch.
If it is compression, then it is time for a new fork.
Drago
Legendary Member
- Location
- Suburban Poshshire
I'd not be keen.
Why would compression indicate a new fork, I thought it’s extremely hard to crush a carbon tube.
Drago
Legendary Member
- Location
- Suburban Poshshire
It is. And it has been.
midlandsgrimpeur
Well-Known Member
If it is caused by an impact or over tightening, it can cause fibres to break or internal delamination, both of which are going to result in the tube cracking at some point. I have had two forks replaced previously where the headset has become loose, this caused the fork steerer tube to compress as it pressed against the bearing race. The compression caused indentations and eventually cracked the steerer tube on both occasions (two separate bikes).
Mike Ayling
Veteran
- Location
- Melbourne Downunda
Don't know but it would not be a problem with a steel fork.
midlandsgrimpeur
Well-Known Member
No, but it would have rusted by now 😉
ColinJ
Puzzle game procrastinator!
- Location
- Todmorden - Yorks/Lancs border
Like this one!
I saw the rider walking his bike after he felt the fork flop about and nearly snap off on a fast descent...
As for iffy carbon... I wouldn't trust it!
midlandsgrimpeur
Well-Known Member
Like this one!
View attachment 772569
I saw the rider walking his bike after he felt the fork flop about and nearly snap off on a fast descent...
As for iffy carbon... I wouldn't trust it!
Blimey, anyone that let's a bike get in that state shouldn't be allowed on the road!
ColinJ
Puzzle game procrastinator!
- Location
- Todmorden - Yorks/Lancs border
I thought that when he showed me the damage!
Oh dear I might have start looking at some steerer tubes now.
Composites are only strong when loaded in such a way that the fibres are subject to tension along their length. Crushing forces typically create large components of off-axis compressive loading so will cause failure at much lower stresses than ideal tensile loading would suggest.
Another problem with composites is that they can degrade internally through delamination with little to no external visual indication.
As others have said the mark on this fork looks typical of that left by the stem - because it's been over-tightened and/or has a burr on that edge. Either way it's likely that the damage extends beyond the superficial indentation on the outside.
This is why it's extremely important to ensure stems have sufficient clamping area, have no burrs or sharp edges, are clamping over the steerer tube bung, aren't mounted excessively high / with many spacers and are torqued to an appropriate level.. factors it seems even manufacturers have a problem getting right, let alone when they're released into a world of mechanics and owners who are unaware of these necessities.
While on paper forks are an ideal application for composites due to the significant mass saving and vibration damping characteristics, they're also one of the most critical parts in terms of the consequences to the rider of failure.
