Question Mavic Ksyrium Elite / Yksion Pro UST - tyre "aneurysm"

Apr 6, 2020
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I bought a pair of Mavic Ksyrium wheels 25 mm (tyres included) and have to say I've been hugely impressed. Apart that is from the tyres...

A few months after buying them I noticed a huge bulge in the tyre wall of my front tyre. It was about 2" long. I thought I must have damaged it, so replaced it, only to find a week later that the back tyre went the same way. A friend who had bought a pair about one month before experienced the same thing with one of his wheels, though he'd bought from a different outlet. Maybe a bad batch...?

I took mine back to the shop - their only suggestion was that I'd over-pressurised it. I don't have an air-shot, just a track pump, so was sure this couldn't be the case. I therefore bought two more tyres, and a digital pressure gauge.

The digital pressure-gauge confirms the one on my track pump is very accurate. Since then, I've pumped the tyres up to 70 psi at a normal speed, then slowly take them up to 80-psi. I can honestly say that the tyre pressure has never gone above 85 psi (I weigh 85kg, so think that's about right...).

And this weekend, I get the same thing on my rear tyre. The tyres look as good as new, apart from the bulge. Whilst the tyre is as hard as you'd expect for one pumped up to 80psi, the bubble on the tyre wall is really soft. It's as if a very thin outer layer of the tyre has separated from the inner material.

I don't have disc-brakes...the brake blocks certainly aren't rubbing the tyre.

Is this a common theme with these tyres? If yes, then what's a better alternative (bearing in mind, these tyres were designed for this wheel).
 
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I think that 85psi is likely too little and the tires are getting damaged by the rim contacting the sidewall when hitting a bump. The pressure needs to be high enough to ALWAYS prevent rim pinching - regardless of the hype and science of lower pressure being more efficient because the tire 'rolls over' small bumps instead of bouncing.
 
Apr 6, 2020
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Interesting...I was erring on the lower pressure to prevent this bubbling, but I guess rapid deformation of a soft tyre wall may cause this sort of damage.

So, various questions spring to mind:
  • If I weigh 85 kg and I have a carbon bike, what pressure would one recommend for Mavic Ksyrium Elite wheels with Yksion Pro UST tyres? Same front and rear, or different?
  • I note that there's now Yksion Pro UST 2 tyres available....anyone tried them?
  • Were I to try a different tyre (though that would be going against Mavic's pairing of wheel to tyre) then what would people recommend (based on actual experience)?
I'd like to find the right answer quickly...at about £50 a tyre, it's turning out to be an expensive experiment.
 
I only have experience with 'old school' road tires and rims. My method was to pump them hard.
And it might be that your troubles aren't due to pressure, but a defect in the tire. But if pressure is low enough for bumps to pinch the rim and sidewall, that's not good.

Jay
 
Apr 6, 2020
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Yes, my first thought was a defect in a tyre, but I know of 4 tyres:
  • One that came with the wheels (bought NW England)
  • Two that came with the wheels (bought E England)
  • One replacement (bought E England, several months after the first)
If defects were that common, then surely there would be more noise on the internet? Mind you, we now have Yksion Pro UST 2 .
 

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