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If I know that when I need a spare inner tube, I'll need a 700c x 25mm inner tube, what would be the point of buying 700c x 23-32mm inner tubes?

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There can be a reason: you have several bikes with tires in that range and one set of roadside repairs tools. Having a tube that can take a wide range of widths allows you to have one spare tube in your kit that will work with several bikes. Note that this reasoning is also true if you want to simplify the spare parts management at home, have several bikes, and be able to use the same spares with as many bikes as possible.

Otherwise, the answer to the question might not be in the intrinsic characteristic of the tube, but to commercial considerations (=why is such product on the market).

In the comments, there's a reference over an entry-level Decathlon tube. This product is a low cost proposition (I don't mean it the bad way), meant to an audience that is not primarily interested in performance, but in a price point. Decathlon might want to sell such tube instead 2 references with a 5mm range from commercial reasons: it allows them to order/manufacture larger quantities of the same item (economies of scale), and having less references also simplifies inventory management, which contributes to meeting the price point.

On the other side of the spectrum, there are also TPU tubes that offer that range. First, high-end manufacturers are also interested in simplifying inventory management and in economies of scale, and second the benefit should be noticeable. I see for example that a 23-32 TPU tube weights 35g, which is ridiculously light. They may make a version that would be rated for 23-28 tires, but if it weights 34g instead of 35g, it may just not be worth the hassle of keeping 2 product sizes.

Now if weight or performance is your concern, the question should rather be focused on the material the tube is made from, rather than the range of size it is rated for, as the two are also linked.

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  • Re: "I don't mean it the bad way" Thanks for stressing this. All too often in cycling (as elsewhere) uncritical folks will use "cheap" to signal "of poor quality", which only leads to gratuitously dear products. That said, 23-32mm is not exclusive to budget-priced or generic products of unknown provenance. Pirelli, for one, also produces such an inner tube.
    – Sam7919
    Sep 11, 2023 at 20:41
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Actually, I am not sure there is such a thing as a 23-32mm inner tube. That is an immense size range. 23mm tires have much less internal volume than 32s. If you told someone from the era when 23mm was the accepted standard that people were contemplating 32mm tires on road bikes, and on aerodynamic wheels to boot, they would either laugh, or cry, or laugh and then cry.

On a cursory Google search, I saw one listing for 18-23mm tubes. That’s not a huge difference, and I bet butyl for a narrower tube can stretch. In any case, almost nobody makes tires under 23mm anymore - I have a feeling that 23 is soon to become a casualty of the move to wider rims. I’ve seen tubes rated for 25-28mm or so. I used a latex tube with that size rating in a 23mm tube, and it was an acceptable fit, and I experienced no problems.

I see one Tubolito tube rated for 18-28mm tires. That’s a TPU tube. It may be fitted for a very narrow tire and still be able to stretch to a 28mm tire. I have no inside knowledge. It seems like bad practice if they really meant 25-28mm, only we’ll just list narrower sizes since who even rides those anymore.

Otherwise, I’ve seen listings for tubes for 28-32mm tires, which seems like a plausible range.

25mm tires are not very wide at all. If you had a tube that could expand out to 32mm, it would probably be too wide to fit into a 25mm tire. I wouldn’t feel comfortable using it, anyway.

Conversely, I have said that standard butyl tubes for 23mm tires have been used in cyclocross tires in the past, and it was fairly common practice. Yes, it exceeds the tube rating, but it seems that in practice it was ok for a few races - with the caveat that I wouldn’t do this to light butyl or latex tubes.

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    Re: "I am not sure there is such a thing as a 23-32mm inner tube." Here is one decathlon.com/products/… that's sold worldwide.
    – Sam7919
    Sep 11, 2023 at 2:12
  • Re: "If you had a tube that could expand out to 32mm, it would probably be too wide to fit into a 25mm tire," well, that's exactly my question!
    – Sam7919
    Sep 11, 2023 at 2:12
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    Partly regarding of @Criggie's point there's a non-technical factor:the rareness of 18mm means a specialist product, probably for a weight-conscious rider, but a small amount of inherent stretch means it's OK up to 23. A tube thick enough to stretch to 32 but still thin enough (when new) to fit 23 covers the vast majority of road bikes. That means a non-specialist shop can cover more uses with one product line
    – Chris H
    Sep 11, 2023 at 5:38
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    @Criggie Maxxis makes an "ultralight" 33-50mm tube, that's a 51% increase. I've used them in 42mm tires.
    – oscu0
    Sep 13, 2023 at 12:14
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    @oscu0 fascinating - clearly "percentage increase" isn't a linear metric. Perhaps it's exponential ?
    – Criggie
    Sep 13, 2023 at 19:28
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Most tubes are sold in compatible ranges rather than specific "one-size" configurations, I guess that would make product portfolios a mess since many brands even offer multiple valve configurations and you have 3 different lengths for Presta valves, a "light" model, latex tubes, extra puncture protection, etc... tires got wider over the years and the cycling community was never running just "one size" for a long time, so you always needed some flexibility in tube size, that's not just the recent trend of running 28-30 mm on many full-road configurations.

So, you should be fine with a 23-32 mm offering for your 25 mm tires. I run 20-25mm-specified tubes on 25 mm tires for years and had no problems except unavoidable punctures.

These "ranges" are a calculated and tested tolerance in which the tube is stretched out flush on the lower end but also not stretched beyond the material's capabilities, so safe to ride. Just try inflating an old tube without tire casing and see how large it gets before it finally explodes.

Just don't exceed these ranges and fit something that doesn't even include your tire size, maybe except from a 23-mm spare tube as a lifesaver on big ride (but I would back off from something too large because it might not sit well well and won't last too long without puncturing, anyway)

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