Tube Size

[Twilkes]

This isn’t quite a Friday Physics Question, but for my 700c-28 tyres I can buy a 700c 18-28 inner tube, or I can buy a 700c 28-47 inner tube. Is there a difference using a smaller tube at the top end of its range, in comparison to using a larger tube at the lower end of its range?

 

[ianrauk]

Both will be fine. You wont notice any difference.

 

[400bhp]

I guess the larger one is (duh) larger, and hence heavier?

(ever so slightly) more faff to carry a spare etc?

 

[Rickshaw Phil]

As Ianrauk says you won't notice any difference, however having said that I would personally pick the smaller of the two because:

• The smaller tube will be very slightly lighter.
• I have had a large tube in a tyre that was at the bottom end of its range fold over itself and eventually fail at the fold. (It was a cheap one though - probably wouldn't happen with a good make).

 

[Twilkes]

So it's not like it will affect the pressure, or the larger tube won't be able to get up to as a high a pressure as the small one in the same sized tyre - it's just the amount of rubber that is kicking around inside the tyre?

What would happen with an 18 innertube in a 47 tyre?

 

[Rickshaw Phil]

So it's not like it will affect the pressure, or the larger tube won't be able to get up to as a high a pressure as the small one in the same sized tyre - it's just the amount of rubber that is kicking around inside the tyre?

That is correct.

What would happen with an 18 innertube in a 47 tyre?

The honest answer is, I don't know. What I suspect would happen is that because the rubber would be stretched more than it is intended to, you'd run the risk of it tearing if punctured rather than just having the small hole you'd normally expect.

This is of course pure speculation as I haven't tried it.

 

[shouldbeinbed]

18 in a 47 would be like a balloon with the skin stretched wafer thin, much more prone to punctures by jarring and tiny nasties inside the tyre that would be absorbed by the correct grade tube