The little sealant that could … n’t

With rain in the forecast today (although it’s since turned out to be fairly nice weather) I decided to have another go at the tiny leak on my rear tire. This is for the wheelset that is now my spare since I swapped the wheels almost a month ago. And that swap was prompted by this same leak, which vexed me on my recent ride to Yokohama.

The leak was originally a little pinhole caused in all likelihood by a bit of glass I ran over. It was a gradual enough leak that I didn’t notice it when I filled up the tires, but it would cause the rear to lose enough air over the course of an hour’s riding that the rear would be noticeably soft.

In other words, exactly the sort of leak that sealant should be able to fix up.

Man up and fix it

To date I’ve tried the following fixes, with identical results:

  • Adding more sealant, swirling it around and reinflating the tire
  • Putting a plug in the hole, adding more sealant, etc.
  • Leaving it sit for a couple of weeks and then trying again
Bicycle tire separated from rim, with tire boot on inner surface
Tire firmly booted

When I first picked up the tire in the Workshop in the Sky this afternoon, I was surprised to find it was holding a good amount of pressure. Not fully firm, but perhaps about 20psi at a guess. By contrast, the front tire (with a slow leak around the valve) was utterly flat.

Starting with the rear, I pumped up the tire as it was. Everything went fine until about 45psi, and then suddenly the hole opened up beneath the plug and all the air came whooshing out.

Right, then. Obviously this is not working. So I got my tire levers and unseated one bead. Pulled out the plug — it came out quite easily, which is not a good sign. And then I cleaned the inner surface of the tire and applied a tire boot. I pressed it on good and firmly all around. Then I reseated the tire, made sure there was enough sealant in it, and put on the pump.

The tire inflated immediately, popping onto the rim snappily, but the hole continued to leak as before. The boot had had no effect. I quickly tried to snap a photo of the sealant jetting out of the tire under pressure, but it was finished by the time I grabbed my phone.

This obviously wasn’t getting me anywhere. The hole in the tire was much larger than before, owing to the plug, but it is still well below the size at which it should be a challenge for the sealant.

Detail of bicycle tire against wall with sealant leaking on floor
That’s … supposed to be in the tire

Now it’s just getting stupid

I decided to fight another day. I cleaned up the spilled sealant and put the tire aside. Then I turned my attention to the front. It’s got a tiny leak around the base of the valve. It probably means I should retape the rim, but again, this should be well within the ability of the sealant to fix. I shook the tire to verify that I could hear sealant sloshing inside, and then I pumped it up. As expected, I heard a hissing noise from the valve.

I picked up the tire and swirled it around, shaking it back and forth to get the sealant in the valve area. After a moment, a small pool of sealant emerged around the valve. Air bubbled through the sealant. I shook and swirled a bit more, expecting that at any moment the sealant would take hold and the leaking would stop.

And … no dice. No matter how I shook and swirled, the air continued to hiss out from the base of the valve.

Disgusted, I put away my tools and washed up, thinking the while.

Change the sealant!

Is it possible my sealant is just crap? It’s from Schwalbe, a top tire maker. If they don’t know latex, who does?

Anyway, I decided to have a look, and I quickly came across this review of tire sealants. I’d expected Stan’s to be at the top, but a careful reading of the text showed this is not the typical Stan’s but a special formulation. The surprise in the test results (in which they poked holes in a tire and timed how long it took to seal) was that Schwalbe came in 4th place. That and reading that it’s in fact made by Stan’s (but isn’t the special sauce recipe that took first place in this test).

My bottle of Doc Blue is almost empty anyway, after all my tubeless travails. I’ve ordered a bottle of the Stan’s Race Sealant, and a couple of spare valves for good measure. I also found a 140ml pouch of sealant, perfect for carrying in the saddle bag in case a big leak causes a huge sealant loss on a ride. It’s Muc-Off, not Stan’s, but I ordered a couple anyway.

The goodies will arrive tomorrow, but it may be next weekend before I have a chance to give it all another go.

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