Front Carbon rims juddering

cd03wba

After doing a very big steep climb (Mt. Fuji 5th Station) I started to descend and when I applied my front brake, apart from squealing very loudly, the whole front of my bike started to judder quite violently.

I immediately stopped and inspected the rim. There was no discernible damage, warping or discoloration to the carbon.

On further testing, I noticed that the rim brakes consistently "bit" at the same point on the rim and caused the brake pads to complete lock up the wheel at that point only. I checked for a bump at that point on the rim but there isn't one. The spoke at that point is also fine.

The rims are Campagnolo Bora Ones and I'm using the appropriate Campagnolo carbon pads for Shimano Dura-Ace rim brakes.

The wheels have been used for about 2 years without issue in exactly the same setup and there has never been a problem other than them being pretty noisy when braking hard.

I regularly ride pretty big climbs but don't really "push it" when descending. Braking has always been a bit noisy and I admit that both the rims and pads could probably do with a good clean.

I wasn't going very fast as the road is pretty steep (1 in 7) but I was braking extremely hard and both brakes front and rear were complaining quite a lot!

I've checked the headset and forks and they are fine.

Have I somehow damaged the carbon in one place and one place only? Are they somehow contaminated in the same place?

Any observations or advice would be gratefully received.

sungod

it may simply be contamination/pad residue

try cleaning the brake track, i'd use acetone or isopropyl alcohol - don't get this on any decals etc. as solvent may damage them

i.bhamra

Have you checked that the rim is still in true?

cd03wba

sungod said:

it may simply be contamination/pad residue

try cleaning the brake track, i'd use acetone or isopropyl alcohol - don't get this on any decals etc. as solvent may damage them

Yes, I will do.

It's strange that it's only in one area though.

The trouble with cycling in Japan is that you have to assemble and dissamble your bike whenever you travel on passenger transport.

So it's quite possible that grease has got on to the rim but I don't understand why it's only one small area.

cd03wba

i.bhamra said:

Have you checked that the rim is still in true?

Yes. It's still true.

The pads are equally worn and not worn out, as well.

cd03wba

OK... I just got home and took the wheel off... There is definitely a bump on the brake track of the rim! A small protrusion about an inch long towards the tyre part of the rim. No cracks or scratches or discernible chips.

Is this a result of a bump in the road or has the brake track melted somewhat?

I wouldn't have expected carbon to dent as such, so any ideas?

I've used them for approximately 18 months... 🤦🏽‍♂️

sungod

a carbon fibre rim can deform under high impact, i've had this happen after hitting a pot hole very hard at high speed, no chip or crack visible, but the edge of the rim was deformed, the case of mine the wheel was checked by the manufacturer and had to be replaced

i've had another wheel with what looked like just a chip on the edge of the rim (piece of sharp debris in he road), but internally the rim bed had a crack, i rode it for hundreds of km without realising, then when i removed the tubular and glue i saw it, dead wheel

i suppose heat/other damage could cause surface brake track damage that even if not fully repairable, might still be safely rideable (but annoying if braking is pulsing)

but as you can see/feel the bump, i would get it inspected properly by the manufacturer/authorised repair agent

with campag it can probably be rebuilt with a new rim, or see if they have a replacement discount program

cd03wba

sungod said:

a carbon fibre rim can deform under high impact, i've had this happen after hitting a pot hole very hard at high speed, no chip or crack visible, but the edge of the rim was deformed, the case of mine the wheel was checked by the manufacturer and had to be replaced

i've had another wheel with what looked like just a chip on the edge of the rim (piece of sharp debris in he road), but internally the rim bed had a crack, i rode it for hundreds of km without realising, then when i removed the tubular and glue i saw it, dead wheel

i suppose heat/other damage could cause surface brake track damage that even if not fully repairable, might still be safely rideable (but annoying if braking is pulsing)

but as you can see/feel the bump, i would get it inspected properly by the manufacturer/authorised repair agent

with campag it can probably be rebuilt with a new rim, or see if they have a replacement discount program

Thanks. I though as much.

As I've only just moved here (Tokyo) I'll have to research who deals with Campagnolo to see if I can replace the rim.

I've looked into sourcing another front wheel or wheelset but as they're rim brakes and clinchers it looks like they're few and far between.

I could really do with keeping up my training...

i.bhamra

As sungod mentions, taking the tyre off might help in identifying any delamination or crack. I thought delamination in one small area sounded unusual but the picture below suggests it's not!

cd03wba

Yes, very interesting. Whilst I haven't taken the tyre off yet, that looks very similar to mine.



There is only a slight roughing up of the outside of the brake track but the "bump" does cause pulsing, when applying the brake fully.

It seems to me I'm going to right off the wheel?

Is there any mileage to try to sand it down using fine sandpaper? I've got nothing to lose?

cd03wba

This is a close up of the area.

cd03wba

Although you can feel the bump, you can't really see it from above.

I guess there might be some delamination but it doesn't seem to have broken through the surface.

I'm totally aware of the dangers but am wondering whether I could sand it down enough to avoid the pulsing and use it carefully until I source an alternative?

I really could do with continuing my training and the problem I've got is that I'm no longer in the UK, so it's not so easy to ring around and get a replacement delivered.

sungod

at least take off the tyre and look for any sign that the rim edge has deformed or cracked

if it really is 'only' a surface bump, it might be due to overheated brake track

but i'd still say get a proper check done, a cf repair specialist should be able to inspect with ultrasound etc. to understand what the extent of damage is

a quick google finds... https://carbondryjapan.com/ their english site says they do repairs https://commerce74.wixsite.com/egcdj/about

cd03wba

sungod said:

at least take off the tyre and look for any sign that the rim edge has deformed or cracked

if it really is 'only' a surface bump, it might be due to overheated brake track

but i'd still say get a proper check done, a cf repair specialist should be able to inspect with ultrasound etc. to understand what the extent of damage is

a quick google finds... https://carbondryjapan.com/ their english site says they do repairs https://commerce74.wixsite.com/egcdj/about

Yes. Thank you. I'll take a look. I've also contacted Campagnolo here in Japan and ordered some new wheels.

As it looks doubtful it can be repaired, it would be great if I could just get the rim replaced but I don't hold out much hope.

I'm still minded to see if the lump can be flattened somewhat, just to allow me to use the wheel without putting it under undue stress.

Although the lump isn't of any great size it is still sufficient to make the wheel pulse under any amount of braking.

cd03wba

I've just removed the tyre. There is a slight bulge.

Would applying heat enable this to be pushed in?

I've contacted Campagnolo here in Japan but as it's Golden Week, haven't heard back yet.

Even though I've had them 2.5 years, do I have any recourse? Or leverage?

Ultimately, I'm happy to pay the costs of the repair. Or even the cost of new rims. I'm just wondering whether Campagnolo have a policy of accident replacement for wheels?

First.Aspect

That can't be repaired and you should not ride on it.

Get hold of a cheap front wheel of any brand if you and desperate to get back on the road.

joeyhalloran

This happened to my old carbon rims too. The problem is it's a compounding issue in that the spot which is raised will then contact the pads harder and get hotter which causes more deformation, etc...

lesfirth

As above. Do not ride on it.

sungod

^^^ do not ride, that's a dead wheel

imho that is heat damage: once you exceed the glass transition temperature for the resin it will soften

that's especially bad on a clincher rim as the pressure pushes it outwards and it stays like it once cooled, it's fortunate that the tyre didn't blow off the rim

the transition temperature varies with the resin, some wheels are better than others in this respect

steep descents with a lot of braking can cause heat to build up, cf doesn't conduct heat that well, so the brake surface can be much hotter than the inside, but given time the whole section can heat up and soften

pulsing the brakes 1 second hard/release/repeat allows the wheel to shed some heat, fwiw lightweight say their wheels will lose about 50 celsius per revolution

if it's really too steep and twisty to brake that way, just keep stopping to check the rim temperature (careful touch with a wet finger), you can manually spin the wheel to help it cool

masjer

A carbon fibre expert's opinion on what bike parts shouldn't be constructed from CF.
4:27 the part about brake tracks, in line with sungod's post
It does seem that CF wheels are better suited to disc brakes, especially in the mountains.
https://youtu.be/TPcm7-KvytI

sw19carpenters

Wheels should be easy to come by in the land of Shimano no?
Time for disc brakes?