Would you ride on this fork?

[martinn]

Hi All,

I have had an issue with a fork of mine, the amount of brake rub has significantly increased. This occurred with three different wheels. There is a whole thread about it.
So I finally got round to replacing the fork. and have taken a couple of pictures.

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This is Carbon /Alu fork 5 years old, all weathers. I couldn't see any bubbling or corrosion of the paint work around the interface sites, but I could see marks on both inner faces of the fork. I ride with mudguards, and they are at that level, so I presuming that this is related.... and is most likely causation, but I have two questions.
1) if the marks are caused by the mudguards what was the mechanism, and how can I stop this in future
2) Would you ride on this fork?

thanks

Martin

[andrew_s]

1.
I would suppose that the mudguard was touching or almost touching, the fork at the site of the damage. Mud (aka grinding paste) will have accumulated in the gap, and the continual small vibrations and larger movements will have been rubbing away at the fork. I'd both add a strip of copter tape there, and bend the mudguard inwards to increase the clearance to 1 mm or a bit more (hot air gun), provided that didn't bring the mudguard into conflict with the tyre.

2.
Given that you'd changed the fork to cure a problem (and presumably succeeded?), no, I wouldn't ride on it.
I would suppose that the damage had weakened the fork enough that increased flex was causing your brake rub problem, and given the consequences of a fork failure (and carbon failures are often sudden), I wouldn't take the chance.

I wouldn't expect to see any paint bubbling as evidence of damage in carbon. You get bubbling in steel and aluminium because the corrosion products (rust, aluminium oxide) are bulkier than the original metal. In carbon, you're looking at cracks and failed bonds, neither of which involve any change of size in advance of actual failure.

[pwa]

With most other parts of a bike I would say that is just cosmetic damage to paint so just carry on using it, but with a fork I would not take any chances. Especially as you suspect that flexing has increased.

[tim-b]

Hi
Here's mine; this is the worst blade

1) Mine is mud/mudguard "fretting". Cleaned up, protective tape added and ridden since April '18. Mine is resin layer damage only and doesn't penetrate to any fibres
2) Only you can make that decision. Galvanic corrosion could be hidden anywhere that the two materials meet, however, this would be an unlikely manufacturing problem rather than something that afflicts every CF/alu component; manufacturers use a neutral layer, e.g. GRP, between the two materials
Regards
tim-b

[Polisman]

To be honest that wouldn't bother me at all. Forks, IMHO aye very, very hard to break.

[Brucey]

...I have had an issue with a fork of mine, the amount of brake rub has significantly increased. This occurred with three different wheels. There is a whole thread about it.....

Would I ride that fork?

Sorry to be blunt, but it is an emphatic "No" from me.

Honestly it doesn't matter what it looks like, it appears to be flexing in an abnormal fashion. If you want an opinion on it that is worth something, take it to someone who can inspect carbon fibre (UT and/or X-ray etc) and get their view on the matter. The chances are pretty good that there is a serious fault with it, if its behaviour has changed. And it won't have been caused by something that just rubbed the paint a bit.

A problem with CF is that it can be merrily delaminating internally (or coming disbonded at adhesively bonded joints) with little sign on the outside that anything is amiss. Asking opinions on the look of the thing, on the basis of a few photos (which BTW are completely out of focus anyway) is highly unlikely to tell you anything of real value.

Abnormal flexing such as you have observed is about as much of a clue that something is wrong with that fork as you would ever expect to get; plenty break with far less warning than that.

If the fork fails in service it will be likely to cause a serious accident. Ask yourself what risks you are prepared to take with this part; my guess is that most folk would consider odd of 1 in 1000 as being 'too high'.

cheers

[Vorpal]

The part that would bother me about that fork is

I have had an issue with a fork of mine, the amount of brake rub has significantly increased. This occurred with three different wheels. There is a whole thread about it.
So I finally got round to replacing the fork. and have taken a couple of pictures.

If it was just the mark, no problem. That looks cosmetic, and (as others said) is just caused by vibration of the mudguard. Given your other problems with this fork, I probably wouldn't chance it, though I might play with it in the workshop to see if I could figure out the specific source of the problems.

[pwa]

The one little niggling thought that might stop me binning that fork is that the increase in brake rub could just be due to a friction problem with the brake cable. Unlikely in a front brake but just about possible. So long as I were happy that this was not the case, I would be very suspicious of that fork and I'd get rid of it. It isn't worth the risk. As Vorpal says, it isn't so much the paint damage as the apparent change in the way the fork performs. It seems to be giving a warning, which is very helpful if you listen to it.

[martinn]

Thanks for the reply's.

I might use some helicopter tape where the mudguard would sit before I install the next fork, in the hope that this would prevent/ delay the surface damage.
Interesting thought about the excessive brake rub being a cable issue, but I haven't changed anything so why would it suddenly start?

Thanks

Martin

[pwa]

Thanks for the reply's.

I might use some helicopter tape where the mudguard would sit before I install the next fork, in the hope that this would prevent/ delay the surface damage.
Interesting thought about the excessive brake rub being a cable issue, but I haven't changed anything so why would it suddenly start?

Thanks

Martin

Quite right. It wouldn't suddenly start, and I do think it is unlikely. It just occurred to me that it would unfortunate if you binned the fork then found the brake rub was actually caused by a minor brake malfunction.

I am a strong believer in putting tape on vulnerable areas to prevent damage. And if the tape starts to wear, replace it from time to time. Perhaps those clear strips you buy to prevent cable rub would do it. And think about filing a bit off the guards if they need it.

[Brucey]

IIRC in the other thread the amounts by which the wheel moves laterally (under load) are well described. The deflections reported are far more than normal and (apparently) have increased since the fork was new. Other comparable forks don't deflect the same amount with the same wheels installed.

Any one of these things is of sufficient concern to prompt the fork to be scrapped or subjected to a thorough inspection by a competent person. Under these circumstances, worrying about a few apparently superficial scuffs is pretty much a complete irrelevance.

cheers

[pwa]

IIRC in the other thread the amounts by which the wheel moves laterally (under load) are well described. The deflections reported are far more than normal and (apparently) have increased since the fork was new. Other comparable forks don't deflect the same amount with the same wheels installed.

Any one of these things is of sufficient concern to prompt the fork to be scrapped or subjected to a thorough inspection by a competent person. Under these circumstances, worrying about a few apparently superficial scuffs is pretty much a complete irrelevance.

cheers

The OP thinks the scuffs may be a bit more than that and may have initiated the apparent failure of the fork's structure. Obviously if you think that, and you are getting a new fork, you want to avoid a recurrence. In reality we don't know that the scuffs have anything to do with the failure, but the symptom of increased brake rub does make the fork sound suspect. The cause of the failure of the fork may not be related to the scuffs, of course.

[Cyril Haearn]

I think Brucey is right, one does not know, but the fork could suddenly fail catastrophically
Best not to use it