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[Apologies if this seems like a dup: I see there are lotsa tire+tube questions, but this one does seem to be slightly different, in that it strives for generality and concerns choice between alternatives.]

question

Suppose one is buying tubes for a given {rim, tire} tuple. Assume the following data/constraints:

  1. The tire fits the rim's bead seat diameter (BSD) appropriately and has tire width w1.
  2. Tubes ta and tb match the rim/tire BSD and are identical in all meaningful1 respects except width: identical cost, material, thickness, valve, etc.
  3. ta specifies a width range w0-w1 (with w0 < w1)
  4. tb specifies a width range w1-w2 (with w1 < w2)
  5. One is a competent tube changer with lots practice.
  6. One's primary concern is tube reliability over time: i.e., one very much wants to have fewer flats.

Given the above,

  1. Are there empirically-valid reasons to choose ta (i.e., the tube for which the tire width is at the high end of the tube's width range) over tb (i.e., the tube for which the tire width is at the low end of the tube's width range), or tb over ta? Or is there no reason to prefer one over the other?
  2. Are there other data/constraints which are significant for the decision? E.g., whether one typically runs at high or low tire pressure?

motivation

I drive recumbents with 20-in/406-mm front wheels, currently running unbelted 20x1.35 Primo Comets. (FWIW

  • tire make/model is irrelevant for the rest of this question, so feel free to ignore.
  • I don't drive a trike: I have 2 nearly-identical SWBs with swappably-identical wheels. I like to have spares :-)

) I bike for transportation, so reliability is very important to me. Unfortunately

  • I recently moved to an area with much more puncturing road debris.
  • The area is also less dense, causing longer mean trip distance which exposes me to more debris.
  • Recent flats have now consumed my stock of 20x1.35 tubes. FWIW, I replace tubes rather than patching them (assume that preference as given :-), and I like to keep a few spare tubes (as well as ... everything else).

Fortunately there are some 20x1.5 Kevlar-belted Comets locally available at a decent price, which I intend to try. However the 406-mm tubes I'm seeing (and on which I now need to stock up) are either 20x1.25-1.5 or 20x1.5-1.75. Which raises the more general question.

possible answer

I bought the 20x1.5-1.75 for the Primo belted Comets. After 3 months: no problems installing, no flats, hold air well (i.e., takes a long time to go from 90 psi to 80 psi). Granted, this is not much of a test: n=1, not enough time for testing, change of tires is a confounding variable. But WTH.


1 Assuming both tubes have the same material and thickness, the wider tube will be heavier, but consider the mass difference negligible. (In this specific case, the mass difference=26 g, which is negligible for me.)

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    Do consider patching your tubes rather than simply chucking them out. Its an easy skill to learn and apply, and you can patch tubes until the patches would overlap, the valve goes bad or tears out, or a cut is just too long. – Criggie Dec 5 '15 at 6:14
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    All that and then consider the mass difference negligible. Ignore the most significant difference between the two tubes? – paparazzo Dec 5 '15 at 13:20
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    If (as specified) either tube is within spec, the difference will be negligible. Certainly any benefit from the tube will vanish in comparison to the benefit of kevlar tyres. Once you have debris pushing through the tyre and encountering the tube, the best you could hope for from a tougher tube is that it lasts a tiny bit longer (slime etc. ignored). – Chris H Dec 5 '15 at 14:55
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    Match the tire width as best you can, and, if you must fudge between two equally "not quite right" matches, choose the one on the smaller end. But this will have negligible effect on punctures -- for that you want Kevlar belted tires. (And learn how to patch your tubes.) – Daniel R Hicks Dec 6 '15 at 1:08
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    @Frisbee: in this particular case, the mass difference=26 g. I ride for transportation: 26 g is totally irrelevant to me. – TomRoche Dec 6 '15 at 1:10
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You say to ignore mass. Why ignore the major difference between the two tubes?

Mass = rubber. The two tubes may start with the same wall thickness but inflated to 1.5 the larger tube will have stretched less and will have a larger wall thickness at the inflated size.

The best measure would be weight but if you take 1.5 / 1.25 the inflated wall thickness of bigger is 20% greater. What is the chance an object would penetrate the smaller wall but not the larger? Very small; nevertheless, the larger tube gives a thicker wall at the inflated size.

You can buy puncture resistant tube with thicker rubber. With the larger tube you are getting thicker rubber for free. It's as if you were buying socks, and your foot was between sizes, and the different sizes were the same price. The bigger socks will have more cushion and last longer.

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    I'll add that good tubes will fit even bigger wheels than recommended one. I saw a 26" tube on a 27.5" wheel with wide tyre that works just perfect. But as @Frisbee wrote, the thicker (not too much, but by a small amount) tube in most cases will be better. – Alexander Dec 6 '15 at 13:57
  • @Frisbee: "When you boil down all those words the basic question is: For 20 x 1.5 tire which tube would be more reliable?" No, there is a more general question (which is why I phrased it the way I did) independent of any particular tire BSD or width. – TomRoche Dec 6 '15 at 23:13
  • WFM: see last section of question regarding why I'm taking this as answer. – TomRoche Mar 26 '16 at 3:16
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If you're getting flats regularly, my guess is that its not the tube's fault, but you to need to make sure that you have sufficient tire pressure and switch to puncture-belted tires (e.g. Schwalbe Marathon). A tube is just a balloon, and you can often put a tube marketed for a not too different size tire into one which slightly different without problems (so long as you don't have the extra width bunch up; e.g. don't put a 29x2.5 tube in a 700x18 tire; I normally do this with 700x23 marketed tubes in a 700x28 tire without problems). Just like most balloons, even the smallest prick will deflate it, so you really need to protect the debris from getting to the tube in the first place. The thickness difference between the rubber in the bigger and smaller tubes will likely be too small to make a difference. And in this case, since the tube is designed to work for tires of your size in both cases, you should expect to have perfectly acceptable behavior with both sides (that is, dumb luck should determine which works better).

Empirically, if anything, the brand of tube might have a slight effect. I've had bad luck with tube reliability from one manufacturer in particular, so I don't buy their tubes anymore.

If you're really paranoid, they make tubes which have extra thick rubber called puncture resistant tubes (useful if you have goatheads) and you can fill your tube with tire sealant (Slime). These will be more resilient to punctures compared to other tubes, but they are more expensive and Slime is messy. But I'd start with some puncture resistant tires. In short, if you don't have these speciality tubes, its likely the case that it doesn't matter which tube you have.

I'd suggest avoiding using tire liners, since they can actually increase flats unless you're really not in good shape. A puncture belted tire is a better idea for most people.

  • The link you gave asserts that liners can cause flats without giving any evidence. Other knowledgeable people say otherwise, and if you have tyres that otherwise suit you they're a good option and cheap. If you're buying new tyres I'd always go for anti-puncture. – Chris H Dec 5 '15 at 18:53
  • @chrish The flats come from friction/abrasion. If your tyre liner is stretched it shouldn't move much. If its an old tyre with the bead cut off, or a tube cut in half, then the edges can rub their way through the innertube. Talcum powder helps reduce this, but it takes a lot of riding to rub through a tube. Other possibility is there's something wrong with the tyre leaving an open space/less pressure in one spot, permitting movement. – Criggie Dec 6 '15 at 2:46
  • If your tyres are in good shape, liners will be a very decent choice. Even if you will put it in wrong few times, you will learn by it how to put it right, and then you will not have any more problems. What you need to do for this is to cut the liners right way (or ask LBS to cut it right way for you), and when you get flat, inspect the tube to see why the puncture occured. The only place that liners are really a problem is rear wheel of folding electrical bikes. The pressure there causing the liner to pinch the tube very commonly. – Alexander Dec 6 '15 at 14:04
  • @Batman, may I add I recommend tire liners when the application asks for it. The key information from the link I read is "... if incorrectly installed causes flats." Agreed tire liners are challenging to install and get straight. I've never seen a flat caused by a liner. I did a 600+ coastal ride and ran over palm fronds and nails riding low light conditions, no flats for the whole ride. I testify tire liners saved my bacon in harder commuting/touring conditions. – Cerulean Fish Dec 9 '15 at 2:03
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The things that will make your `bent more puncture resistant are

  • Not riding on or through things that give punctures (not always possible)

  • Higher tyre pressures

  • Thicker tyres - just more rubber on them.

  • Belted tyres (reinforced with something)

  • Tyre liners (either real kevlar bands, or old tyres with the bead cut off)

My preference is for higher pressures and not crashing through potholes and over kerbs. I've tried puncture resistant tubes and there's not enough data yet. They are heavier and thicker than a fast tube.

ANSWER 1: Punctures are a part of cycling and cannot be completely eliminated. Carry the tools and two spare tubes. (one for each size, perhaps two for each size being a good one and a patched one for cost reasons.)

ANSWER 2: To answer the question of your question: the tube's rated tyre size is a range, and a smaller 1.2-1.5" tube will stretch more to get to 1.5 vs a 1.5-2.0 tube that will have to stretch less. A more-tightly stretched tube will be more vulnerable to puncturing over time.

However that means the foreign object has already penetrated the tyre. Expecting the tube to resist the FO means that its already on the inner line of defense against flats.

Logic says a the bigger-rated tube will do better, but the cost is the extra mass. Consider weighing both sizes of tube and compare the difference - I have this data point:

  • 26" MTB tubes 190g and 212g (both with a patch) vs 560g for a new puncture resistant tube. Sadly I can't read at what width the tubes are rated.

FINAL ANSWER You'd be best off using puncture-resistant tyres and tubes if reliability is your top priority, and suffer the weight penalty. Still carry spares+tools.

  • So basically you're asking if a slightly wider tyre is better or worse at getting punctures? Read the question. Inner tube - not tire. – paparazzo Dec 5 '15 at 15:16
  • @frisbee You are correct. From the motivation section of the question "currently running unbelted 20x1.35 Primo Comets" and "some 20x1.5 Kevlar-belted Comets locally available" Last time I looked 1.5>1.35 therefore larger which also means wider. A wider tube in the same-size tyre will simply stretch less to fill the same space. The Question part of the question does refer to different tube sizes only. – Criggie Dec 6 '15 at 0:49
  • @Criggle: I'm interested in the 20x1.5 because they are Kevlar-belted and the available 20x1.35 are not. Net: in section=Motivation I am not asking if a slightly wider tire is more puncture-resistant. – TomRoche Dec 6 '15 at 1:16
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    @Criggle: I don't drive a trike, but I can see how you might have inferred that, so I edited the question. – TomRoche Dec 6 '15 at 1:32
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    @Criggle: FWIW, {small front, large rear} has been the dominant design for recumbent bikes for awhile. {both large wheels} forces either odd chain routing (e.g., FWD) or odd seating position (overly reclined for anything but racing); {both small wheels} requires serious gear ratios to achieve speeds normal for recumbents. – TomRoche Dec 6 '15 at 23:09
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Major edit for this, told a story before so I'll completely re-word. If the question is assuming new 26 x 1.5 Kevlar tire which tube would be used of two choices and why? A top of fit tube width of 1.25 - 1.5. Or slightly over sized at 1.5 - 1.75. Note *** All sizes in inches.

Answer: I would always go with the "top of fit" 1.25-1.5 tube for choice. My experience has been a smaller width tube that is not over sized will fit easier in the tire on installation. Why? The over sized tube means you have a greater chance to pinch the tube in between the tire bead and rim wall. Interesting over sized does work it's just not preferred. With a repair shop banging out flat repairs or personal use it's more challenging install to use the "over size" 1.5 - 1.75 tube. An over size tube also causes balance issues. The tube is slightly bent and twisted on install to achieve fit. I've ran Specialized FAT BOY slick 26 x 1.25 tires, with Kevlar and always used 26 x 1 tubes.

One caveat here, in my original answer I was just suggesting and cautioning don't let the range of size difference (tire to tube width) get too great. So as my previous example, a 26 x 2.5 tire with a 26 x 1.125 tube that combination with a 0.375 variance went BOOM and destroyed the tube and tire.

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    Did you use a compressor to fill the tire? Sometimes those put air out a little too quickly, so you overfill by a lot more than you think you do. That being said, it may have just been a bit of bad luck. – Batman Dec 5 '15 at 14:53
  • You not actually answer the question that was "which is better: bigger or smaller". You simply say "take the one that fits", but they both fit... Some customers are pretty newbies in bike terms, and easily mistake between 2.125, 2.25 and 2.5.. – Alexander Dec 6 '15 at 13:54
  • Re-worded answer, concentrated on tube bigger or smaller and why. Thx, point taken @Alexander. – Cerulean Fish Dec 9 '15 at 1:45

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