My rear tire on my Kawasaki keeps losing pressure - I have to top it up every week or so. I checked for punctures and didn't see anything obvious. Is there something else that could cause a slow leak? Should I just bite the bullet and get a new tire or could it be the valve stem?
The bead seal is worth inspecting too - when a tire doesn't seat properly on the rim, air can escape there without leaving an obvious puncture. Before dropping money on a new tire, try rotating it to a different position or remounting it with fresh bead sealer to see if that fixes it. If the pressure still drops after that, then yeah, valve stem replacement is cheap and worth doing anyway as preventative maintenance.
Check the valve stem first - that's the most common culprit for slow leaks and costs way less to replace than a tire. If it's not the stem, the leak could be coming from the bead (where tire meets rim) or a tiny puncture you missed, so a tire shop can do a proper soap-water test to pinpoint it before you drop money on a new tire.
Before you assume it's the valve stem, make sure you're not dealing with a slow puncture that's hard to spot - sometimes they're tiny and don't show up until you soak the tire in soapy water. That said, the valve stem is definitely worth investigating since it's cheap and quick to replace, and a worn one can absolutely cause what you're describing. If that doesn't fix it, then yeah, the bead seal between tire and rim could be the issue, especially if the rim has corrosion or damage. At that point you'd probably be looking at a new tire anyway since you can't reliably patch a bead leak.
Guys, good points on the valve stem and the soapy water test - definitely start there since both are cheap to rule out. One thing I'd add: if you do the water test and find nothing, try remounting the tire on the rim yourself or have someone do it, because sometimes just breaking the bead and reseating it fixes a slow leak that nobody can actually see. I had this happen on my bike and spent weeks chasing a phantom puncture before realizing the tire just wasn't seated right. New tire should be your last resort here.
Slow leaks on a single wheel usually come down to three things, and the valve stem is genuinely the cheapest fix - so that's worth testing first with soapy water around the stem itself to see if bubbles form there. If that's not it, the other answers cover the main suspects pretty well.
What I'd add is a practical step: once you've ruled out the stem and done the soapy water test on the tire, try deflating completely and inspecting the rim where it meets the tire. Sometimes you get corrosion or debris sitting on the bead seat that prevents a proper seal, and you might not see it just by looking. If the rim looks grimy or oxidized, a quick clean with a wire brush can actually fix the leak without any new parts. Have you had a chance to do the soapy water test yet, or are you still at the visual inspection stage?
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