18-25 or 25-32

chefyong

Hi,

I noticed that there are 2 kinds of tubes in the market for a 700 x 25c rim, an 18-25 and a 25-32 tube. I searched and found only 1 answer to this question and to quote "18-25 there is risk of a tear at the valve. With the 25-35 there is risk of fold over flats"

is this correct??

Thanks for your feedback.

Anonymous

Do not think either size option is more prone to either of those problems.

I guess 'fold over flats' means pinch pictures, and as long as tyre is correct pressure you should be fine. If anything the thinner one would be more likely to pinch puncture as it will be thinner.

If it means that the tube is folded within the tyre then, regardless of flatting, I would go with the 18-25 out of those two options as the idea of having an overly/unnecessarily big tube in a tyre seems wrong.

As to tears at the valve, just make sure you do not push the valve back into the rim when you attach a pump when topping up pressure, as it will put a lot of strain on the joint around valve.
If your valve is threaded then use the backnut (its only real use) to stop this happening.

ForumNewbie

chefyong wrote:

Hi,

I noticed that there are 2 kinds of tubes in the market for a 700 x 25c rim, an 18-25 and a 25-32 tube.

These are not the only options as the tubes I use are 20-28. I use them on 23,25 and 28 tyres without any problems.

Initialised

A fold over flat is when you have to fold the tube to fit it inside the tyre, hit a lump hard near the fold and there's a risk of a flat at the fold. I've had this happen using a 1.5 tube in a 1.2 and using a 28 in a 23.

Tearing off the valve immediately after swapping the tube after a flat is really annoying. You can avoid this by putting the nut/washer (backnut?) on the valve on the inside of the wheel. The nuts with a raised edge for using presta tubes on schrader holes work best for this.

On that choice of tube I'd go with the larger size as the tube will be thicker and therefore that much more resistant to penetrative punctures.

Anonymous

Why would you put a tube in a tyre if it does not fit without 'folding'? :shock:

You do not really need to use the nut after swapping a tube, you just hold it from the outside of the flat tyre to push the pump onto the valve.
You more need the nut to top up a partially inflated tube/tyre as you cannot push down from the outside then.

Not sure a slightly thicker bit of butyl with 100 psi behind it is going to withstand a thorn etc that has just pierced your tyre................unless it was on the bit that was folded over lol.

Mark Alexander

I can only say I recently made the mistake of getting the larger and it was more difficult to fit. I'd recommend the smaller.