Symptoms
- Tire feels slightly soft each morning despite inflating the day before
- No visible flat, just gradual pressure loss
- Happens consistently over several days
- Valve area feels slightly warm or has residue when checked
Likely causes
- CommonVery small puncture (slow leak)A tiny hole can leak slowly enough to not be an obvious flat but still lose noticeable pressure overnight.
- CommonWorn or loose valve coreA valve that doesn't seal perfectly will slowly leak air.
- PossibleNatural air permeability through the tube materialLatex tubes especially, and to a lesser extent butyl tubes, lose some air naturally over time, which is normal.
- PossibleLoose valve extender (for deep rims)A poorly sealed valve extender on deep-section rims can leak slowly.
What to do
- Note how much pressure is lost overnight; a few PSI is often just normal permeability, especially with latex tubes, while a rapid drop suggests a leak.
- Check and tighten the valve core with a valve core tool if you suspect it's the source.
- Submerge the inflated tube in water briefly to look for a stream of bubbles indicating a puncture.
- Inspect the tire tread and inside surface for a small embedded thorn, wire, or glass shard.
- If using a valve extender on deep rims, check that its threaded connection is sealed properly, sometimes needing thread sealant.
- If no leak is found and pressure loss is minor and consistent, this is likely normal permeability and just needs regular top-offs.
- If pressure loss is significant and no cause is found, a bike shop can help pinpoint a hard-to-find leak.
Tools and parts
- Valve core tool
- Bucket of water
Bike inner tubeSearch: “bicycle inner tube”
When to call a pro
A bike shop can help find a very small, hard-to-locate leak if home methods don't turn up the cause.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.