A couple of weeks ago when I rode my Plus mountain bike I noticed half way through my ride that the rear wheel rim seemed to be bouncing off bumps on the trail, I stopped and put some more air in and set off again on my merry way, not thinking any more of it. A week later I came to ride the bike again and discovered that the rear tyre had gone completely flat.
I had converted these wheels to run tubeless last summer so I knew it wasn’t going to be due to a traditional puncture, it would require some time to investigate the air leak, it would most likely be one of three things – air escaping through the tyre sidewall, a tiny gap at the rim (possibly caused by the tyre burping at low pressure, something which I don’t think was the case now), or a faulty valve; I pumped up the tyre to 20 PSI (max riding pressure) to see how long it would take for the tyre to go flat, it took about a day or so, so I knew it had to be quite a slow air escape.
Today, being several days later, is the first chance I’ve had to spend some time looking at the problem so I set to with pump, tyre levers, and spare sealant at the ready.
First thing I did was remove the wheel from the bike and pump it up to 20 PSI, then listen and look closely at the tyre, paying particular attention to the sidewall. After some time I narrowed down a slight hiss to an area of the tyre near the valve, though it was not coming from the valve but through the sidewall, I could see some tiny bubbles of sealant leaking out where the canvas pattern was in the sidewall.
After confirming where the air was escaping I popped the tyre off to check the sealant level, and I was astonished to find that the inside of the tyre was bone dry! The sealant had adhered to the inside of the tyre and probably just run out, leaving one area without enough sealant to properly seal the tiny holes in the sidewall. There was only one thing for it – add a load more sealant and hope for the best, so that’s exactly what I did. After refitting the tyre and pumping up to 30 PSI (installation pressure), then tilting and swirling the tyre around to ensure the sealant moved over the entire inside surface I listened again – no air escaping sound could be found.
I checked the front tyre and found almost the same situation, although this time there was a tiny trickle of sealant and the inside of the tyre looked wet at least; I added another dose of fresh sealant and put the tyre back on the bike. Time will tell if this has cured the problem, fingers crossed!
In conclusion, if there’s a ‘slow puncture’ on tubeless tyres then first thing to check should be the tyre sidewalls, look for a tell-tale diagonal stripe pattern and sealant escaping along lines following the pattern of the canvas that makes up the tyre carcass. Check that there is enough sealant sloshing around inside the tyre (at least one inch depth), add more if it’s running low or dry.
It’s interesting to note that I haven’t had this problem with my Vittoria Barzo 2.2 tyres, only the Specialized Ground Control / Purgatory 3.0 tyres; no doubt their construction differs, if I had the luxury of being able to try a different 3.0 tyre pair on the Plus bike I would, however after plenty of internet research the consensus from users is that this Specialized tyre combo is perhaps one of the best so it’s worth persevering with for now. Hopefully with more e-bikes using 3.0 size Plus tyres the available selection will improve in time.