Quoted message said:I get given a lot of bikes from family members as their kids grow out
of them and I try to check them and pass them on for re use.
I've noticed the cheaper mountain bike types with inner tubes having
car tyre type valves seem to lose pressure quickly. A check with a
bubble over the valve doesn't indicate any air leaving via the valve.
Is it just an issue of cheaper tubes being more porous? They seem to
need re inflating once a week yet I seldom need to re inflate the
tyres on my road bike with conventional bike valves.
Doesn't necessarily relate to price. Some expensive tubes are made of
very thin material to save weight, so are naturally more porous than
thicker tubes*. Some manufacturers claim their brand of butyl holds air
better than others, but I bet size and thickness are bigger factors. Not
all cheap tubes are thick, though.
Narrower tyres tend to need topping up more often, so it's unusal for fat
MTB tyres to go down quicker. Maybe your road bike has particularly heavy
tubes, or maybe all the MTBs happened to have very slow punctures that you
missed.
Presta and car type valves rarely leak at all, though older Woods valves
often did.
* 20 & 23mm high pressure tyres with these can need topping up every 3
days or less if fussy about maintaining pressure to within 10 or 20 psi.
~PB
