R5 Carbon Fiber Seat Stay Tire Rub Damage

Question

I have a 2012 R5 frame. This past weekend I put 25mm tires on the bike for the first time. All clearances looked good when I had it on my stand and when I tested the bike. I went out on a long ride and I started to hear tire rubbing when I got out of the saddle and the frame flexed. I tried not to get out of the saddle for the rest of the ride and when I got home I took off the wheel to look at the rub. See images below it appears some paint and a first layer of carbon fiber was "rubbed" by the tire. It is clear that I have to go back to 23mm tires on the rear, my question is should I be concerned about the damage to the frame. My gut says 1mm of rub is fine but I do not have any experience with this type of damage. Additionally, the rear seat stay is pretty thin given the frame is from 2012.

Thanks in advance for any help / commentary. I truly love this bike and have been taking great care of it for years.

Answer 1

Unfortunately, I believe this needs to be repaired. Remember that carbon fiber is composed of layers of carbon that are all cured in an epoxy matrix. If you look closely, you can see concentric rings in the damaged area. Each ring is a layer of carbon fiber. A carbon fiber structure derives its strength from all the layers being present. Additionally, damage can propagate under load. That said and to be fair, that last point applies to delaminations, and I'm not 100% sure this would happen with abrasions. But I wouldn't chance it

This type of damage occurred to a lot of bikes at Unbound 2023, a gravel race with one section that had highly abrasive mud. You should seek a carbon fiber repair shop. This is likely to be a relatively simple repair.

For a more general treatment of what to do if you suspect carbon damage, you can read here. That page had been updated to cover abrasion damage. Here's another sample photo of abrasion damage that's gone through a few layers of carbon.

When changing tires, I suggest using an allen wrench as a feeler gauge. An example is below.

This is the rear seat cluster of a 2007 custom road bike that was built for what I said were "wide 23mm tires". The concept that someone might want to ride 25mm tires was still new at the time. Anyway, the tire is a nominal 25mm tire, which measures 26.4mm wide. A 6mm allen key just fits between the tire and the nearest point on the chainstay, suggesting just barely 6mm of clearance. There is more vertical clearance than that, so I didn't bother to measure as the chainstay clearance is the limiting factor.

I believe that ISO standards call for 5 or 6mm of clearance between the tire and the nearest point on the frame (I forget which it is). You can push things somewhat. If I mounted 28mm tires, they would probably inflate to 29.5mm or thereabouts. That would leave me with ~4.5mm clearance at the nearest point. This should be OK. I bet that at 3mm you are tempting fate. The wheel would hit the frame if it came out of true, or if mud got clogged in there - although this is a road bike, and if there's that much mud, I am walking.

Answer 2

SIDE THOUGHT: clearly 25mm tyres are too big for this rear triangle. However the positive side is that a carbon fibre framebuilder might be able to "widen" the seatstay gap.

This alteration would be more work than repairing the existing rubbing, but since you're up for the repair cost anyway, the difference in cost is an upgrade opportunity.

Find a local expert at carbon frame repair and discuss the options of a wider brake bridge.

Also, check the chainstay clearance - no point widening the seat stays if the chain stays have the same width limitations.