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How Does Tubeless Sealant Work?

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Posted By: Mason Copeland

Dec 27, 2021
NSMB: 2-Minute Expert 
Words: Pete Roggeman Photos: Deniz Merdano
2-Minute Expert is an NSMB series that distills technology and other concepts into short, easily digestible articles.

On the face of it, the premise behind tubeless sealant is as simple as blood clotting to seal a wound. Like cut skin, if a tire sustains damage, sealant is propelled towards the hole by the tire's escaping air pressure, and as long as the 'wound' isn't larger than the sealant's ability to clot and stop the loss of air, a new seal is established. Simple enough. But the inner workings of sealant are more interesting as well as more complex than that simple analogy.

The Latex Issue

The words latex and tubeless sealant are almost interchangeable, because latex has traditionally been both the best and pretty much only basis for sealant. Despite its ubiquity in most sealants, latex is not great stuff - it's not good for the environment, first of all, and it's a terrible allergen for some. Those two alone could be enough to condemn latex, but leaving them aside, latex also carries some performance deficiencies that really call its de facto dominance into doubt. Let's have a look at those.

Latex Issue #1 - it dries out
The latex used in most tubeless sealant is defined as a 'dispersion of polymers in water' and the main drawback of them is that they dry out in use - both in your tires and in your valves. This is annoying, but also means your sealant (and eventually your valve) becomes ineffective over time. It dries because as you ride, your sidewall flexes, exposing pores to the air outside, allowing the aqueous part of the sealant to escape.

Latex Issue #2 - it relies on a process similar to coagulation to work properly
Going back to our original analogy, latex works like blood to seal a tire's wound. That's fine, but larger wounds require help to seal - hence the use of additives in many sealants, like glitter, pepper or gluten. Some of these are harmful to the environment, but they all play havoc with your valves, reducing your valve's efficacy until it has to be replaced.

Latex Issue #3 - it won't work if it freezes
Once frozen, latex becomes unusable, so for use in cold temperatures, you need to use nasty chemicals like methanol to help it retain its liquidity. This is the same as with latex paint, which is unusable at freezing temps (below 0ºC or 32ºF).

Sidewall Seepage

It's common to see sealant seep through the sidewall of a new tire, and not surprising that our instinct is to think that's a bad thing. Sealant is supposed to seal that sidewall, so if it's coming through, it means the sidewall is not robust, right? Not exactly. Sidewall seepage happens because as you ride, your sidewall flexes, opening pores and letting the aqueous part of your sealant escape. This is your sealant doing its job - rushing to the rescue to plug a hole, or many small ones in this case - not a bad thing. However if too much sealant escapes, it accelerates the drying process on the inside of the tire, meaning you have to replace it or top it up more often (or in the worst case, being dried up and ineffective when you need it). Another thing: if the seeping sealant evaporates quickly and disappears from the sidewall, that means it's a volatile substance, (many sealants contain volatile, harmful substances like ammonia) whereas if it stays in place on your sidewall, it's not volatile (nor harmful). Sealant on the sidewall is not bad, and a quick wipe and it'll be gone - all the better if it's a safe substance you're wiping off of that surface. The volatile substance evaporates, making you think there's no problem, when in reality your sealant is literally evaporating into the air, losing its effectiveness and requiring shorter service intervals.


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