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Smaller inner tube than recommended?

Old 06-21-20, 09:43 PM
  #1  
shed
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Smaller inner tube than recommended?

My bike shop sold me 700*20/28c Specialized inner Tubes for my 700*32 Trek SL5 Domane, and I got another flat first time out.

I checked tires, and wheels, nothing broken or sticking out.

Question:just coincidence? Should I be going for a larger inner tube? In general do I want my inner tube to be rated on the lower side (like this) or the upper side compare to my tire (like a 700*32-50)

Also any recs on tubes recommended?
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Old 06-21-20, 11:58 PM
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Miele Man
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Carefully check the tire for anything that might be embedded in it. I had a tire once that had picked up a very fine piece of wire (much like a piece of brake or derailleur cable wire if it was one strand) and it was stuck in the tire. I had to remove the tire from the rim and then flex the tire so that the metal piece intruded into the inside of the tired and then using a needle nose pliers, pull the piece of metal out. A cotton ball run along the inside of a tire, to check for sharp objects, can prevent a cut finger or thumb.

An undersize tube will have to stretch more to fill up the larger volume of the tire and that can make the undersize tube more prone to punctures s it's now thinner than it would be if it was a proper size tube.

Cheers
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Old 06-22-20, 03:24 AM
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Not ideal, but super small difference, and probably not the cause of your puncture.
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Old 06-22-20, 05:00 AM
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Originally Posted by Miele Man View Post
Carefully check the tire for anything that might be embedded in it. I had a tire once that had picked up a very fine piece of wire (much like a piece of brake or derailleur cable wire if it was one strand) and it was stuck in the tire. I had to remove the tire from the rim and then flex the tire so that the metal piece intruded into the inside of the tired and then using a needle nose pliers, pull the piece of metal out. A cotton ball run along the inside of a tire, to check for sharp objects, can prevent a cut finger or thumb.

An undersize tube will have to stretch more to fill up the larger volume of the tire and that can make the undersize tube more prone to punctures s it's now thinner than it would be if it was a proper size tube.

Cheers
A microfiber cloth works better than a cotton ball and will cover more area faster.
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Old 06-22-20, 02:43 PM
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A slightly undersized tube is usually easier to mount correctly in the tire. I can see why they recommended it. For a home mechanic, it reduces the chance that you'll have part of the tube pinched between the rim and the bead, which could lead to a flat or blowout.

I doubt that the small amount of extra stretch in the tube contributed in any way to the flat. A regular 23 mm butyl tube can get about as thick as a coke can before it blows.
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Old 06-22-20, 02:52 PM
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As others have said, it shouldn’t be an issue. But if you get a larger tube one day, it does have to be stuffed into the tire. I run 25’s and use a 25-32 tube for the same reason as already stated; less stretch so slightly thicker. It does take some effort to spread out the larger tube size when mounting the tire. No problem once mounted, but a little more effort getting there.

John
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Old 06-22-20, 03:02 PM
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I carry 700x32-40 tubes as a spare on my mountain bike. It's way smaller and lighter. I'm certain that it would mount just fine on a 29x2.25 tire.

Tubeless works so I haven't had to find out but I am sure I could get back on that.

Your tire went flat because something let the air out of the tube. Probably a thorn. Possibly a pinch flat. Remote chance the valve is messed up. The size of the tube isn't the problem.
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Old 06-22-20, 03:04 PM
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I always use a size smaller. Easier to install and pack, a bit lighter.
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Old 06-22-20, 04:26 PM
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Originally Posted by andrewclaus View Post
I always use a size smaller. Easier to install and pack, a bit lighter.
I always use a tube one size smaller than the tire for the above resaons.

I have a bike with two sets of wheels, one with 23mm tires, the other with 37mm tires. I carry the same ~21mm tube in my saddle bag and can use it with either tire for roadside tube replacements. That's a bit further than I usually take it (I usueally use a ~32mm tube with the 37 mm tire). But it works fine.

I never get a flat unless there's something causing it, either a leaky valve or a puncture from something I ran over on the road (90% of my flats are from tiny wires from steel belted car tires). Never just happens because the tube is too small.

For example, pump up a tube by itself. Then you won't wonder if it's OK to use a tube that's rated smaller than the tire.
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Old 06-22-20, 08:02 PM
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On a similar note, how do you all feel about using a 650 size tube on a 700 wheel?
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Old 06-22-20, 08:10 PM
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ddeand
650c tire is 571mm
650b tire is 584mm
700c tire is 622mm
I'd suggest buying a 700c tube
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