wrong size inner tube

Cycleops

Guru
Location
Accra, Ghana
Amazing what will suffice in an emergency. Better than having to walk it.
 

Dogtrousers

Kilometre nibbler
Not recommended but I got away with a 700c x 20mm tube on my MTB today ( with 35mm tyres). I forgot to swap spare tubes in my bag this morning as I changed bikes today as ut was raining !!
Some time ago I stopped to help an MTBer in distress at the roadside. He had punctured and didn't have a spare tube. I offered him one of my spares but he thought I was mad. I'm pretty sure it would have been an effective get-you-home. In the end I gave him a packet of Skabs and left him to it. (I suspect he had already phoned or decided to phone for rescue).
 

SkipdiverJohn

Über Member
Location
London
Neither too small or too large is advisable, as a small tube will stretch a lot so the wall of the tube runs thin, and too large a tube may not even inflate to the correct shape so could have folds and twists inside it that could stress the rubber too much. But as mentioned, any tube that holds air is better than one that doesn't - to get home on at least. I try to size my tubes to the biggest ones that will inflate correctly, so the tube expands the minimum amount and maintains the thickest wall. I run mostly Schwalbe 35's and 38's on my 700c wheels and have had no trouble with Conti Cross 28 and Conti Tour 28 tubes.
 
OP
heliphil

heliphil

Über Member
Location
Essex
yes its was still 12 miles from work and raining - pumped it up ( as little as I dare) and rode slowly to work - a lot better than walking - apologies it was supposed to be in commuting, not sure what went wrong there !!
 

DCBassman

Veteran
Location
Ten Forward
When I changed the original (to me) 23mm tyres off the Scott, one had a 27x1.25 tube in it. All manner of folds and creases. I'd unknowingly ridden it for many, many miles!
 

andrew_s

Guru
Location
Gloucester
My worst mismatched tube was a 650c x 18-23 tube that had got into the wrong box at the shop, used in a 700x28 tyre.

With the diameter being too small, it fitted the rim like rim tape, so getting it inflated inside the tyre without being trapped under the bead was pretty difficult.
With the tube not having any proper use, it stayed in until the next puncture, which was only a couple of weeks, iirc.

Normally, I use the largest size available that will fit without folds, like SkipdiverJohn.
My experience is that stretched tubes go completely flat immediately on encountering anything sharp, but that unstretched tubes can leak fairly slowly, allowing you to delay changing tubes until you get home.
In one case, I had a half inch thorn through the tube for about 6 weeks, which only needed pumping every couple of days
 
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I used to buy 24 x 1 3/8" "junior racer" tubes for my MTB. They were cheaper than superlight 26" tubes, but pretty similar otherwise.
 

SkipdiverJohn

Über Member
Location
London
My experience is that stretched tubes go completely flat immediately on encountering anything sharp, but that unstretched tubes can leak fairly slowly, allowing you to delay changing tubes until you get home.
In one case, I had a half inch thorn through the tube for about 6 weeks, which only needed pumping every couple of days
Similar experience to me. I've got away with pumping a punctured tyre at the roadside then riding home on it to repair later on several occasions. Another reason to carry a real pump not CO2! Also had a small thorn in the back tyre of my hack MTB that took two or three days to get really soft.
As well as tube stretching, another factor at work here is pressure. Because I value comfort over having my teeth rattled at speed, I don't run the skinniest tyres I can find at the highest pressure I can pump them up to, preferring more sensible sizes inflated to lower pressures. That means the pressure differential between what is in the tyre and atmospheric air is significantly lower, so a puncture will tend to leak more slowly and also the background rate of pressure loss through the rubber and valve core is lower, so the tyres need pumping up less between rides.
 

Tom B

Über Member
Location
Lancashire
I alway have tubes with a max 25c in my 28c. I find the 28c a bit too big.

The problem always comes when I end up punctured an find I have my MTB kit with me on the road bike.
 
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