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I have a new BMC mountain bike in a tubeless 29" setup.

I have replaced stock Vittoria Barzo tires with a better rolling 29x2.1 Vittoria Mezcal (bought new online from Competitive Cyclist).

All was well, had like 100 miles on them, then didn't ride the bike for a few weeks and front tire lost all the air (probably didn't have enough sealant as the same happened with the other one - I'm not experienced with tubeless). I don't hang this bike on the wall, it just sat leaning against the wall. It sat like that for a couple more weeks before I decided to ride it again. I pumped the air into the tire and realized it was losing air fast. Upon inspection I saw that the tire has developed tiny cracks on the sidewall through which the air was leaving (see pic).

cracks in sidewall

I thought it was a defective tire and replaced it with one of the Barzos the bike came with.

Rode it some more, after a few months of riding let it sit for a few weeks again as I was traveling.

Same thing happened with the other Mezcal tire - lost air gradually, sat without air for a few weeks and when I put pressure in, I discovered cracks too big for the sealant to seal, just like the first one. The contact between the tire and wheel was solid, no air was leaving there.

Am I missing something about tubeless tires? Can you not let the bike sit with deflated tires for a long time? Or did I just get unlucky with a pair of defective tires?

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  • Did you contact the shop? They may be aware of a bad batch. Its worth a phone call.
    – Criggie
    Sep 19, 2022 at 4:28
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    Yep, contacted them, they said that tire is out of warranty so they can't help. It's been over a year since I bought them
    – Corvin
    Sep 19, 2022 at 9:51
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    I don’t know if this is a significant contributing effect, but the material that makes rubber black-colored (carbon black) contributes significantly to UV resistance, tensile strength, and abrasion resistance. Perhaps the tanwall construction is inferior in these regards.
    – MaplePanda
    Sep 19, 2022 at 12:26
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    Any electric motor near where you stored the bike? Ozone from an electric motor can pretty much eat tires by - get this - causing cracks. See en.wikipedia.org/wiki/Ozone_cracking Sep 19, 2022 at 18:05

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I think you just got unlucky with some particularly thin sidewalls. It does not look like intentional damage from humans or animals - the sunlight may have had some accelerating effect, but that sidewall looks awful thin.

Your two options are a new tyre or slap a tube in it and get some life out of this rubber.

If sealant did fix this, would you trust these tyres to keep riding on them? Or bite the wallet and buy some replacements anyway?

A tyre should be okay with low pressure, but if there's a fold or crease then the rubber tends to take that as a "set" and may not come back exactly round when inflated. I'd leave a tyre fully inflated without a problem resting on the ground, but I'd not leave it flat for more than a day before repairing.

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    Thanks. Sealant did not fix this and yeah these tires are going to the dumpster. The cracks definitely appeared where the deflated tire was creased around the spot where the wheel was resting on the ground.
    – Corvin
    Sep 19, 2022 at 9:53
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    +1 on the “low pressure for storage is ok, but avoid leaving tires flat with wheels on the ground”
    – RLH
    Sep 20, 2022 at 2:14
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    Also +1, however i'd add that the sidewalls don't look particularly thin to me, that's just how fast supple casings are
    – Andy P
    Sep 20, 2022 at 13:56

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