Weight Weenies

Never seen anything like it. Haven't so much as had a puncture in 8 months never mind this. These are new 30mm carbon rims I was testing out today and the tyre sidewall blew out. Just got them off now for a look and can't figure it out. No debris like glass or anything and the road I was on at the time didn't have any obvious cause. Have a feeling it's related to the rim. Look how sharp the cut is, looks a bit like a knife was at it! I've kinda ruled out that it was a bit of trapped tube under the tyre as I was ultra careful fitting these, you never know though.

Yup... Sharp-edged rim flanges of carbon rims can slit open the tire side. Continental specifically states a warning to that effect. I think Veloflex has a similar, if not even more stern, warning about using their clinchers with carbon rims.
Can't say for sure, but I would put odds on that's what happened to your tire. If it happens again with a new tire, I think you can be pretty sure it's the sharp bead edge on the rim.

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Yeah under 500 miles on this one so.. and the way the cut was right along the rim..

What to do.. are there specific tyres more suitable for carbon clinchers?

my first 4000s did this with Aeolus rims... the 4000sii's have been fine on same rim. Asploded on my wifes' Madone.. luckily it was less then 10mph on a MUP, but it sounded like a gun shot. Sucked that it ended our family outing prematurely though.

Yeah gun shot here as well. Just coming off an icy patch of road too. If it happened a min earlier I'd have been on my bum

Confidence shot a bit now though, just bought 30mm and 45mm of these rims. (Missus and myself)

Shrike wrote:Yeah under 500 miles on this one so.. and the way the cut was right along the rim..

What to do.. are there specific tyres more suitable for carbon clinchers?

I don't think it's the tires so much as the sharp edge on the rim bead. I have a friend that builds and sells his own branded Chinese frames, and has had issues with the Veloflex clinchers on the rims he has used doing exactly the same thing. But the Contis have actually been better in that regard.

@ Cal

yeah these Cosine wheels are Gigantex rims. Pretty budget. Going to speak to Wiggle, and shoot Gigantex an email and see if they got some advice.

- Did you checked with your hands if the rims are sharp?
- How old is the tire?
- Were they used on other rims before?
- What was the exact pressure you used?
- Under what condition did this happen?
- Any other possible relevant things?
- Why do we have to drain out this basic info?

Shrike wrote:@ Cal

yeah these Cosine wheels are Gigantex rims. Pretty budget. Going to speak to Wiggle, and shoot Gigantex an email and see if they got some advice.

What makes you think they're Gigantex?
I've seen 1 post on the tinterweb saying that. Others say Light Bicycle.

Your beef is with the retailer, that's standard trading laws, NOT the manufacturer (known or assumed). See what they say. Wiggle are IME generally pretty good.

There are lots of recorded instances of conti tyres (normally 4000s) failing on carbon rims, I think mostly down to mounting inconsistences, which is why some manufacturers eg Veloflex put a disclaimer on the box.

@BRM Yeah good questions.

Checked the 30mm rim v the 45mm rim I've got. The 45mm seems smoother. The 30mm does have some very slightly perceptible rough parts. So faint though.
newish tyre, around 500 miles, if even that
yes they were on aluminium rims, Fulcrum Racings 5's
92PSI
Easy riding, around 20mph at the time it burst

Anyway, will see what Wiggle and Gigantex say. Honestly wasn't aware carbon clinchers had this issue

The issue is with the sharp edge on the inside of the bead on some carbon clincher rims. Those edges can be super sharp. I once sliced my hand open changing a flat on a Lightweight wheel by inadvertently sliding it along the edge of one of the carbon spokes as I turned the wheel around. The edges of carbon can be very sharp.

On a Lightweight? Christ. I have a thin carbon file I use for steerer tubes, is it okay to run it faintly along the inside of the bead if there's any sharp parts?

Other comment

History shows that some batches of particular tires (more than one brand), had more problems with sidewall defects/sensitivity than other batches. Find your batch number so people have some reference if they also have probs. Also mention the exact model please.

It was the spoke edge of a Lightweight carbon spoke that cut my hand, and that had nothing to do with getting the flat tire... that was just a normal flat from road debris. Just used that as an example of how sharp a carbon edge can be.
I don't know what's "ok" to do and not "ok" to do on those rims, but if they were mine, I'd probably see if I couldn't feel for some sharper areas of the bead that might be causing the issue then take some Emory cloth and see if I couldn't smooth it out a bit. But I'd want to make absolutely certain I wasn't "rounding" the bead that holds the tire on, as this might result in the tire to be blown off the rim. Before you do anything, why not contact the manufacturer and let them know what happened and see what they have to say.

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@ Cal, yeah rounding it off is my worry too. See what Gigantex say. Wiggle I doubt will be any help.

@BRM 4000s II, no clue what the batch number is though, maybe hoke through the bin later