Why do my tubes lose pressure?

gcwebbyuk

I noticed that my tubes (either conti race28 or maxxis flyweight) always seem to drop in pressure overnight.

They never seem to go below 60 when left for a longer period of time.

I was aware that Latex tubes can lose air, but wasn't aware of "normal" tubes leaking - other than if there is a puncture.

Is this normal, or does my garage have some magical powers of air extraction?

photonic69

Mine do too. Not a problem as I always check pressures before a ride and adjust as necessary. Usually more worried if I'm going to be late for the club ride.

Alex99

gcwebbyuk wrote:

I noticed that my tubes (either conti race28 or maxxis flyweight) always seem to drop in pressure overnight.

They never seem to go below 60 when left for a longer period of time.

I was aware that Latex tubes can lose air, but wasn't aware of "normal" tubes leaking - other than if there is a puncture.

Is this normal, or does my garage have some magical powers of air extraction?

Check that the valve is screwed in tight.

cookeeemonster

This is normal from what I understand...normal tubes lose pressure like latex but at a far slower rate. Never known a tube not to

cgfw201

Doesn't temperature differential make an impact on this? If storing them somewhere like a garage with a fluctuating temperature during the day I think they can go down more than if stored inside at a constant temperature.

dhungerf

If you use the CO2 cylinder to fill the tyres they will lose pressure quicker than air. CO2 molicules are smaller than Air and can sneak out quicker.

this was just another "Fun Facts with Doug"

Alex99

dhungerf wrote:

If you use the CO2 cylinder to fill the tyres they will lose pressure quicker than air. CO2 molicules are smaller than Air and can sneak out quicker.

this was just another "Fun Facts with Doug"

Air is a mixture, mainly of N2 and O2 molEcules, both smaller than CO2 in mass, and similar in size.

Man Of Lard

Alex99 wrote:

dhungerf wrote:

If you use the CO2 cylinder to fill the tyres they will lose pressure quicker than air. CO2 molicules are smaller than Air and can sneak out quicker.

this was just another "Fun Facts with Doug"

Air is a mixture, mainly of N2 and O2 molEcules, both smaller than CO2 in mass, and similar in size.

Both N2 & O2 are considerably less good at permeating through rubber inner tubes than CO2 (which is the main thing that makes CO2-inflated tubes lose pressure so quickly)

gcwebbyuk

Glad to hear it's normal.

I always test the pressures before and top up - it's almost a little warm up!

I don't remember needing to do this with MTB tyres though - is that because they are a lower pressure anyway?

darkhairedlord

it might be the pressure inside the garage increasing rather than the tubes reducing.
Is it in a submarine?

gcwebbyuk

Yeah a yellow one! Damn why didn't I spot that

davebradswmb

I have always taken it for granted that tubes lose pressure. I guess the thinner the tube the faster it loses pressure. I'm pretty sure I have Continental Race 28s on my commuting bike and I pump the tyres up once a week from somewhere between 4.5 and 5 bar to 5.5 bar.

Tiesetrotter

Yep tubs lose air. My Vittoria CX's go nearly flat over night and always have done.

DeVlaeminck

Vittoria tubs have latex tubes inside though - a normal butyl inner tube should not lose enough pressure overnight to need pumping up unless it's got a leak at the valve or a slow puncture - at least mine never have.