Words and Photos: Mike Blewitt

But how much thought do you put into your tubeless tyre sealant, or the system as a whole? An airtight seal is at the heart of a good tubeless system, so quality tubeless tape and valves are a must have, along with tyres that have a tubeless ready bead and a casing suited to your riding style and trails. Beyond that, running the right tyre pressures will help avoid pinch flats and some cuts. Tyres have improved drastically in two decades, so the sealant tends to be there to assist with porous sidewalls, and to help for puncture repair.

Sealant works as the air rushed to a hole, with the polymers in the liquid slamming into each other at the hole and making a seal. This is why a larger hole is hard to seal, and a small repair can occur without you knowing. The liquid is typically reactive to an environment, so tubeless sealant doesn't last forever, either in your tyres or in a bottle on your shelf.

Testing sealants and not systems

I set out to test 7 sealants by using the same tyre on 7 wheels for a set period of time. Sealants were added to the 29x2.4” Pirelli Scorpion LITE Hard conditions tyre as per the manufacturer's recommendations. And then 36 days later after riding, hanging in a hot shed and general mountain bike use, the sealants were tested for the puncture repair performance. There were no punctures in the test period, kudos to Pirelli on their ProWall casing for that.

Test Procedure

Each tyre was inflated to 22psi, and then stabbed with a 3mm sharp tool near a transition edge block. They were ridden on a mixed surface of road, grass and dirt with a timer on. A time was recorded for when the puncture was sealed, and the pressure recorded.

The tyre was then inflated to 22psi again, without any more sealant, and a 6mm cut was put in near a transition block, but 180 degrees opposite the last puncture. They were ridden again, and timed to repair with the pressure noted. A Dynaplug kit was carried and used when the tyre was no longer conceivably rideable. 

There are a lot of variables to control and this method controlled some of them. Time and temperature will have an impact on tyre sealant, and higher pressures will lose more air before sealing can occur. Take these findings as a single experience, as others experiences may vary. We will test any other sealants in the same manner in future product reviews.

Local input on a global product

Owen Matthews is the mountain biker behind Australian brand Ride Mechanic, and he spent a couple of years testing countless tubeless sealants before developing his own product, Ride Mechanic Hoop Goop. Based on seeing the strengths and failings of just about every sealant on the market, his advice is pretty informed.

“Always setup tubeless dry with no sealant and check for major leaks in the system. Fix them. Then if there are no major leaks add a small amount of Hoop Goop to line the inside surfaces, which builds an in situ thin inner tube. Remove excess liquid after a week of riding, using a sealant exchange kit.”

The idea here is that the sealant, Hoop Goop in this case, makes sure the system is sealed. But by removing it you don't have sealant in your tyre drying out.

“If the tyre deflates with a puncture, add some fresh Hoop Goop through the valve stem and keep riding. It should repair most holes. If it's not effective and the hole is too big (over 5mm) or the cut is on rim-bead area use a plug like the Stan's DART.”

Owen's advice is based on his main finding, which is that most sealants aren't that effective anymore after 4-6 weeks, compared to when they are new. Hence, his recommendation of using sealant to seal the system, then adding it when a puncture occurs, so it's the most effective. It's actually a very fast process!

“If you're racing, on the day before an event add fresh sealant. And then remove it after the race.”

“Apart from setup, a puncture and racing there is no need for any liquid in a tyre. As soon as you put it in the liquid will start degrading becomes less effective. Tubeless tyres are very good, with much better construction than non-tubeless. Often the reason people swear by tubeless is they do not get flats. And this has nothing to do with the liquid in tyre, it's because the current tyres are very, very good.”

AMB's 9 tips for tubeless tyre success