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Specialized 2bliss on Fulcrum UST - slowly leaking


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I put some Specialized 2bliss tyres on my Fulcrum Red Metal hoops. I initially fitted them with inner tubes to push them into shape/ease out of their folded state. A day or two later I pulled the tubes out and pumped them up and heard the bead clicking into place. I initially inflated them up to 4 bar and left them overnight. Next morning the tyres are soft, and following day fully flat.


I reinflated them and checked for any air leaks around the rim with some soapy water, but couldn't see any obvious air leaks, they are soft again now. I cleaned the rims before I initially mounted the tyres.


So: Are tubeless tyres only fully airtight with sealant in (I haven't put any in yet)? Should they hold air pressure just on the basis of the tyre & valve seal?



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There's a reason why our MTB pro team rides 2Bliss tires-they want a tire that can handle the low pressure they run (sometimes 25 psi) for durability and better traction, but they also want light weight. Specialized 2Bliss blends the best of both worlds. It's not your standard tubetype (TT), which is lightweight, but can fall short on puncture resistance and "burps" when used with sealant. And it's not your standard tubeless (UST) that reducespinch flats and the need for sealant, but often adds 200+ grams. 2Bliss is a whole new design that uses TT casing with a special UST bead, replacing the standard UST heavy backing with strategically placed rubber only around the bead. The result is a perfect tire for the discerning MTB rider: low pressure allowance, no burping and fewer grams than its forefathers.


Most of our MTB tires come in the revolutionary 2Bliss configuration, except for Sport models (DH, Armadillo, Armadillo Elite and 29" tires excluded); TT and UST are no more. If you want to run our 2Bliss with a tube, be our guest. Without a tube, just grab a batch of our AirLock® Pro sealant, and you're well on your way to a longer, better mountain ride, again and again




I guess 2Bliss does need sealant then :unsure:

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