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I recently got myself a new Giant Roam 0 with tubeless ready rims and Crosscut AT2 tubeless tires. Everything was assembled at the local bike shop. After having it a few days, I noticed that the tire pressure in the rear tire was going down much faster than the front tire (down from 60 to 30 psi after 3 days), so I tested the tire with soapy water.

On the front tire I found no leaks, and the back tire was leak-free around the valve and bead. However, I noticed some slow bubbling around the molding sprues on the sidewall of the tire (the small rubber hairs from the tire molding process). The same leaks are not present on the molding sprues of the front tire.

Does this sound like a manufacturing defect, or could it be fixed with some fancier sealing compound?

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  • Do you mean that the leakage is through the wall of the tire, or at the joint between tire and rim?
    – Daniel R Hicks
    Aug 17, 2018 at 1:00
  • (You probably need to get the wheel into a tub of clear water, vs just using soapy water, in order to clearly make out the source of the leak.)
    – Daniel R Hicks
    Aug 17, 2018 at 1:02
  • The leakage is definitely coming through the side wall of the tire. After spaying the soapy water, a mound of white bubbles begins to form around the sprue. This happens on the back tire only; it does not happen to the front tire. No such mound of white bubbles appears in the groove between the tire and the rim.
    – Paul Belanger
    Aug 17, 2018 at 1:04
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    I would normally consider the tire to be defective in that case, but you might try laying it with that side down overnight, to see if the glop will flow in that direction. (The other odd possibility is that the tip of the sprue has gotten caught between tire and rim and is making a path for the air. But that case should be obvious on close inspection.)
    – Daniel R Hicks
    Aug 17, 2018 at 1:10
  • The sprue is definitely not stuck in the rim. It's only about 1/8 inch long and poking straight out from the sidewall.
    – Paul Belanger
    Aug 17, 2018 at 1:12

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Sounds like a defective tire. The rubber has not fully filled the mould at the injection point.

Don't mess around trying to fix it. Take it back to the bike store and have them swap the tire for you. That way you'll know you have a good tire that will not fail on you later.

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