Carbon Rim Fracture: how long till failure

Any thoughts on the longevity of this front rim?

It’s a 23mm id carbon MTB rim. I’ve been riding it in this condition for the last week while my new wheel was being shipped. It has had no problem holding air tubeless. I’ve done four rides on it after the event that caused this damage occurred.

I now have my new wheelset, but wondering if this will be safe/reliable to use as a training wheel. Since the rear wheel is fine I’m tempted to put some new tires on the old wheelset and treat them as an alternate set for training/racing.

Ditch that dirty B 10 seconds after you took the pic. Seriously, not something to gamble with (your life).

That is now garbage or a wall decoration. At best, a new dedicated trainer wheel.


Is that a crack or a chip? Looks like a chip. I wouldn’t worry about a chip there.

It’s hard to describe. I should have included a ruler in the pic. It’s about 1 cm long and is not splintered or flex at all.

I’m leaning towards ditching it, which is why I bought a new wheelset. Not sure what to do with the rear wheel though.

If it’s just chipped, it’s on the outside of your bead, it won’t cause any structural issues. If there’s a crack, it will propagate and leave you stranded when the air comes out of the tire. It looks like they have the rim bed and out rim jointed there, there’s a thin layer of carbon there covering the joint, and that chipped.

Try to see if it’s a crack - bending the rim sideways, over inflating a tire on it to stress it, put some air through the rim and put that spot in water & see if bubbles come out, get some UV dye in there (laundry detergent??) (

No way am I riding that outside ever.
1 cm, 10 cm doesn’t matter In my opinion


Cracks don’t propagate in composites in the traditional sense.

What you’re seeing there is delamination.

It’s toast.

I guess you could still ride that wheel because an inflated tyre will push the broken bit back together. However, it is weakened in that area, and another hit on it will likely see the outer bit break too, which can easily result in a blowout. I’d really not risk it for riding outside, especially on a front wheel.

You could show the picture to a carbon repair specialist, but I’d guess with the area where the damage is, there is little they can do.

Use the back as a spare, and maybe pick up another front wheel as a spare too.

Bin - new wheel is cheaper than new teeth.

And significantly less painful too. In the long run the new wheel/wheel set is probably thousands cheaper than new teeth or repairing body parts, not to mention damaging your bike and all the associated road rash. And everyone on this forum would feel bad if you damaged your bike! :wink:

The expected lifespan is 0. Get a new wheel for your own safety. You could hang the old one in your pain cave purely for decoration.

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