Very slow leak

[Night Train]

The tyres on my MTB will go from 60psi to 40psi over about 6-8 weeks. I can't find any holes or leaks when I check the tube in water looking for bubbles. Am I missing something or should I consider this to be normal?

My car tyres will hold 38psi for months on end.

 

[domtyler]

It is a function of the thickness of the tube. Bicycle tubes, especially lightweight ones will be extremely thin and therefore the air molecules will gradually escape.
I pump my tyres at least once a week.

Car tyres will use far more material.

 

[fossyant]

Perfectly normal !

 

[Night Train]

Oh, that's alright then. Thank you.

 

[Scoosh]

You could always pump the tube, put it in water and watch it for 6-8 weeks for a bubble

 

[Arch]

You could always pump the tube, put it in water and watch it for 6-8 weeks for a bubble

Sounds like a decent replacement for Big Brother on C4!

<Geordie Accent>

"Today, in the bowl: Is that bubble a leak, or just dissolved CO2 forming round a speck of dirt?"

</Geordie Accent>

 

[beanzontoast]

I'd call 20 psi drop over 2 months pretty good myself. My 115psi tyres lose 15-20psi in a week, sometimes more.

 

[Arch]

I'd call 20 psi drop over 2 months pretty good myself. My 115psi tyres lose 15-20psi in a week, sometimes more.

yes but...

<lays self open to correction>

if your tubes are at a higer pressure to start with won't they be forcing that pressure out faster...

 

[Gerry Attrick]

How man Arch, I didn't knaa ye cud taak geordie like.

 

[mickle]

If you're using Shrader valves a portion of Stan's No Tubes swilled around inside the tube will reduce the tube's porousity to almost zero (as well as frequency of punc*ures). I use it mostly on those bikes in our fleet which are a pain in the ass to inflate, usually the stupid tiny cheap and nasty 6" tubes installed on micro-bikes, Sinclair A-Bikes and the like which can lose 10psi a day.

 

[TheDoctor]

If you're using Shrader valves a portion of Stan's No Tubes swilled around inside the tube will reduce the tube's porousity to almost zero (as well as frequency of punc*ures). I use it mostly on those bikes in our fleet which are a pain in the ass to inflate, usually the stupid tiny cheap and nasty 6" tubes installed on micro-bikes, Sinclair A-Bikes and the like which can lose 10psi a day.

Please don't say I'm welcome to borrow an A-Bike as well! Dear oh lord, they're awful. Apologies to anyone who's got one - they're fantastically lightweight and compact and all, but I'd sooner walk. To my own execution...

 

[mickle]

Ok. I won't say it.





But you are.

 

[Maz]

I normally check the tyre pressure and top-up the air (if needed) every week or so.