Inner Tube size - what determines it?

[summerdays]

At what point does the inner tube become too big for the tyre? And which determines the pressure on the pump - the wall of the tyre or the inner tube?

These questions have come about as a result of having to fix a p******* two days in a row... I created the second one... I think may have over inflated the tyre as I was having pump interface problems (ie new pump - still getting to know it), and I can't see any obvious debris in the inside of the tyre. For example the pump reads that I have inflated it to just over 20 psi but it feels almost hard. Using my old broken pump I would I felt that that was closer to 40 psi. These are Marathon tyres 26" x 1.75 to be inflated to 45 to 70 psi.

I'm waiting for Mr Summerdays to arrive home to see what he thinks but I thought I would pick your brains whilst I wait. (After all you are so much more knowledgeable than him - creep creep )

 

[tyred]

I should think it is the wall of the tyre that determines what pressure can be used. The tube just provides an airtight seal which expands to fill the tyre and the tyre supports it. In theory, you should use a 26 x 1.75 tube with your 26 x 1.75 tyre but I have often used tubes which were different in size without problem. Just make sure it's the right diameter for the rim - 26 x 1.75 is smaller in diameter than 26 x 1 3/8. If it is marked 26 x 1.XX rather than 26 x 1 x/y then it should be fine.