Specialized Sirrus tube / tyre query

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PpPete

Legendary Member
Location
Chandler's Ford
May sound a silly question .... but how are you inflating your tyres?

If you are using CO2 cylinders they will go soft sooner than with air. Never used CO2 myself, but I believe the molecule is smaller and diffuses through the rubber more quickly ?

My favorite inner tubes are Schwalbe, although I generally use Continental because they are often available with a big discount for volume purchases.
 
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jonnyguitar

New Member
porkypete said:
May sound a silly question .... but how are you inflating your tyres?

If you are using CO2 cylinders they will go soft sooner than with air. Never used CO2 myself, but I believe the molecule is smaller and diffuses through the rubber more quickly ?

My favorite inner tubes are Schwalbe, although I generally use Continental because they are often available with a big discount for volume purchases.

Thanks Pete. I use a Joe Blow pump, not CO2.

I'll look for Shwalbe. For 25c tyres is it best to go for 18-25 or 25-35??
 

battered

Guru
CO2 molecules are bigger than air. They are a carbon atom with 2 oxgens, molecular wt 12+16+16=42. Oxygen (makes up about 20% of air) as O2 has a mwt of 32. Nitrogen (N2) (makes up mearly all the remaining 80%) has a mwt of 28.

Racing car tyres are filled with helium, mwt 4 to keep the weight down. That really *does* escape fast.

I'd hypothesise that CO2 escapes faster because rubber is more permeable to CO2 than air, independently of the (small) difference in molecule size.
 

Crankarm

Guru
Location
Nr Cambridge
jonnyguitar said:
Thanks Pete. I use a Joe Blow pump, not CO2.

I'll look for Shwalbe. For 25c tyres is it best to go for 18-25 or 25-35??

Schwalbe are the best tubes IMHO. SV15 - 700 x 18-28C for up to 15/16mm thick rims.

I used to use Specialised tubes but valves kept failing at the base where they join the inner tube which I suspect is what is happening to your tubes. Tightening the collar around the valve too tightly on the rim can cause the valve to pull away from the tube thus causing air loss.

So I switched to Schwalbe tubes. Never had one fail. Tried Continental tubes as well which wasn't a happy experience either so Schwalbe it is.

HTH.
 
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