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I am running a tubeless setup since September and the switching process has not been easy(lots of small problems) but Yesterday I had the most bizarre occurence of all while riding with a friend. Out of nowhere, my front tire went completely flat. I stopped, looked for a leak, found nothing, reinflated the tire and tried to find a leak. Nothing. I rode another 5k without any hiccups when it suddenly happened again. No leaks, reinflate, ride. Only this time, 500m further it happened again. So I popped a tube in there, finished my ride and went to my bike shop.

The tech over there kindly refitted my wheel tubeless and cleaned everything to inspect my tire and wheel. Nothing out of the ordinary, my tire wasn't punctured and my wheel is good.

What on earth might have caused this? I've been riding these wheels for at least three weeks with new tape and valves without any hiccups (unexplained air loss at the back, but that's a story for another time).

Thanks

More details on the setup:

  • Bike is a Devinci Hatchet gravel bike
  • Wheels should be considered brand new (around 1500km) ENVE SES 3.4AR (25mm internal width, hookless)
  • Front tire is a Continental Terra Trail 40c @ 40psi.
  • Rear tire is a Continental Terra speed 40c @ 40psi.
  • The wheels were setup by my local bike shop after a few back and forth with the initial setup

I was riding easy pavement with an average of maybe 250w at the moment of the event. So no hard rocks, bumps, twists or turns. It was a beautiful sunny and coldish november day (maybe around 4-5celsius).

It's also worth noting that I tried this tire/wheels combo for a 650km gravel bikepacking trip with some bumpy sections without any issue of this kind.

I was riding on road, with my gravel bike. Pretty clean bike path. Tubeless setup was done by the book by the bike shop. So all tubeless parts, no hacks or shortcuts here :)

The rim is "brand new" and the technician at my bike shop confirmed my setup was not damaged and tire not punctured. 40c tires @ 40psi.

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  • Pretty much the same set of reasons as for a tubed tire.
    – Daniel R Hicks
    Nov 21, 2021 at 13:56
  • Might be the tape. Is it going from rim wall to rim wall? Any damage? Feel free to ask about those other small issues too.
    – MaplePanda
    Nov 22, 2021 at 0:41
  • @MaplePanda I think the tubeless taping was responsible for a lot of the issues i had with my wheels at first. (bubbling @ the valve, slow leaks) but i was done again after i talked with ENVE. I had maybe three weeks free of problems until this event
    – Pascal
    Nov 22, 2021 at 0:48
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    Have you checked if the tires are compatible with hookless rims? Continental has for a long time said that their tires weren't, although that's changing and a few of the newer tires do. Could be that they're not seating properly and burping air on corners. My only other explanation is that you have a split or rim crack that is forced open when weight is placed on the bike. It would be hard to identify either when the bike was on the stand. You can generally tell when a tubeless tire has a puncture though as it will weep clear sealant liquid when hung up (or however you store your bike).
    – DWGKNZ
    Nov 22, 2021 at 13:56
  • @Pascal Any chance you could remove the tire and take a pic so we can inspect the tape job? Also around the valve area would be good too I think.
    – MaplePanda
    Nov 22, 2021 at 19:11

3 Answers 3

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In my experience, this type of sudden unexplained deflation is usually valve related.

Check the valve core is tightened correctly (applies to both tubed/tubeless). And for a tubeless system check the valve nut is tight (no need for tools, fingers are fine)

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    I did not check that the nut was correctly tightened at the moment of the incident. Unfortunately it is too late to check now because it has now been redone. I'll keep it in mind if it happens again!
    – Pascal
    Nov 23, 2021 at 3:30
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This answer is premised on the assertion that the tire did deflate with no puncture or other input during normal riding.

It’s possible that the tire bead got dislodged from its seat and that you lost pressure, I.e. you burped the tire. Generally this happens with some sort of lateral force on the tire, e.g. you hit an obstacle on the side of the tire. I believe that in cyclocross or MTB, burping doesn’t necessarily take the whole tire flat, but they run at much lower pressures than road bikes - assuming this is a road bike.

In theory, we would not expect tubeless tires on rims conforming to accepted dimensions to burp. The issue is that the industry only just agreed on a set of dimensions for tubeless tires. The Slowtwitch article I linked said that the ETRTO clarified that the bead seat diameter for tubeless tires is 621.95mm +/- 0.5mm. There may be other parameters involved as well, e.g. the G-height, or the vertical distance between the top of the rim and bottom of the bead seat groove, or possibly others.

My understanding is that at least to BSD, while there was no universally accepted standard for tubeless tires, some rim manufacturers might have built rims slightly oversized from the normal BSDs to give a tight fit. Or some manufacturers may have had higher variances in production (in common speech we might say they had poor tolerances), so they had a number of undersized rims. And then we might need to consider the situation from the tire manufacturers’s side. They have to make their tires to conform to the rims out there, but they did not necessarily know what dimensions the rims were targeting.

Basically, a possible explanation is that your set of tires and rims did not match in some way. If the tires mounted very easily, then possibly the rims were on the low side of the BSD tolerance and/or the tires were on the high side of their diameter tolerance. Or some other set of parameters is at play.

With the rim standards now set and the tire standards forthcoming, figment issues should generally disappear for new tires and rims. Unfortunately, that doesn’t tell us what to do about older tires and rims. If this is a road bike, then honestly, one option is not to run them tubeless. A lot of people aren’t sold on road tubeless over alternatives. Latex tubes produce the same rolling resistance as the same tire set up tubeless, and latex tubes are also fairly puncture resistant. TPU tubes are expensive and probably have a bit more rolling resistance than latex, but they retain air better. Alternatively, if the bike store has experience with your rims, you could ask what tire models they’ve had good experience with.

For what it’s worth, I had a similar experience on a DT Swiss CR1800 wheel set with Panaracer Gravelking SKs, I.e. loss of pressure while riding with no puncture. I didn’t lose all pressure, and not finding any issue, I tried reinflating the tire. Unlike you, I didn’t seem to have that problem again.

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  • Funny enough that ENVE is quoted in the article you linked as my problem happened on ENVE wheels!
    – Pascal
    Nov 22, 2021 at 0:55
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Broadly speaking, the larger the size of the puncture hole the lower the pressure the sealant will be able to effectively cope with.

So first time the tire went down; almost certainly a large puncture where pressure dropped sufficiently that by the time of inspection the sealant had been able to plug. Any sealant that might have been visible, got rubbed clean.

Then - I would guess - the sealant had a bit of a chance to set while reinflating, faffing etc. Which enabled it to cope with a higher pressure and made it appear okay - at least initially - to ride on. However, once underway the combination of tire flex and extra load caused the sealant plug to get blown out and the second catastropic failure to occur.

Subsequently the tech missed the puncture. Easy to do. These type of punctures are almost as hard to find in the workshop as they are in field. Particularly if using, treaded, knobbly tires, where they can lurk at the base of the knobblies. No problems since, could be down to the sealant having enough time set properly. Or could be different sealant - Stans Race or similar will seal most things.

Good luck with it.

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  • In my limited experience of tubeless, a puncture sealed by sealant will be wet on the outside for a good while, at least hours and maybe days.
    – Criggie ♦
    Nov 22, 2021 at 4:13
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    Yep, sealant can and will stay wet if it doesn't cure/go off. The thing is, that when riding any excess sealant that goes through the hole before it is sealed can quickly become difficult, occassionally verging on impossible, to spot on the tire (even with leg decorators). Worth bearing in mind that the 2nd time it went down, the sealant is likely to have plugged the hole again and then had much more benign conditions to effect a permanent fix i.e. much lower pressures trying to dislodge it for hours/days and warmer temperatures - all of which could help the sealant do a better job.
    – shufflingb
    Nov 22, 2021 at 12:28
  • i think maybe 2hours max passed since my first flat to the bike shop getting the wheel checked and "fixed" (cleaned, inspected, remounted, etc...). I then went for a quick tour trying the wheel out, going down curbs, sprinting and riding damaged asphalt and everything looked good. Could I be able to find a sealed puncture on a tire if i looked very carefully or is it kind of an impossible job to do?
    – Pascal
    Nov 23, 2021 at 3:45
  • Hi @Pascal, Depends. If piercer still present - easy by touch from inside - possibly visually from outside. If it is gone - some sealants, e.g. Stans Race, will 'scab' over larger holes, making findable from inside - smaller holes/other sealants, most of the time no dice. I can't vouch for sealants with UV dye, e.g. Muc Off's, which might make it a bit easier. But usually, if it's fixed, the only external mark where the puncture was will be a thin, 1 - 3 mm, slightly darker patch, located somewhere on the outside of a tire with its road dust and tread pattern, i.e. almost impossible ;-)
    – shufflingb
    Nov 23, 2021 at 16:28

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