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BF got a fancy new bike, and promptly punctured the inner tube, I’ve been looking in shops for the right size and getting in a right faff trying to find the right size.

His wheel says on it -(700 x 25c)

I know it’s a Presta Valve, and has to be 700, but I’m confused on the 25.

Does the inner tube have to be 700x25c, or would a 700 x 18-23c fit?

There’s a 700 x 35-38c which I’m sure is way too big, but I’m also concerned that the 18-23c is too small?

Does the inner tube specs have to end in 25? Or include 25 in the numbers? Like say 18-28 would? (Just random numbers)

Many thanks for any help

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  • Look at the box the inner tube comes in. Usually there will be a range of widths listed.
    – Daniel R Hicks
    Mar 29, 2019 at 17:43
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    If you went to several shops (you pluralized it in your question), why not ask the staff there? When I worked retail, this was one of the most common questions I got and I had to explain or sort it out with clients every day. Most bike shop staff should be quite knowledgeable on this subject.
    – Gabriel
    Mar 29, 2019 at 19:44
  • Just go into any bike shop, tell them the tire size (700x25C) and Presta (or Schrader) and they will hand you the correct tube. If you have the bike or the tire with you, they will even change it for you for a few dollars.
    – Michael Hampton
    Mar 30, 2019 at 4:26

4 Answers 4

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The marking on the tire '700 x 25c' means a 622mm diameter rim, with a nominally 25mm wide tire. ('700c' comes from an older French standard for wheel and tire sizes, it's very commonly used to refer to the standard road bike rims and tire size).

Inner tubes fit a range of tire sizes as they are quite flexible. The two numbers denote the min and max tire sizes. A 700 19-25c tube will fit, as will a 700 25-28c. As long as you tire size fit in the range specified you are good.

Note that tires and tubes may also be marked with 'ISO 622' or 'ETRTO 622' These are both equivalent to 700c.

You also need to get a tube with the correct valve stem length. Tubes come with a range of valve lengths to fit different depth rims. The length is not usually marked on the tube but is easy to measure.

The simplest thing to do of course is take the punctured tube to a bike store and simply ask for new tube that is compatible, for a 25mm tire. Or get your BF to buy his own tubes (or learn how to patch them).

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    Thank you for answering my question, it’s helped a bit, although I must say, your tone referring to my BF saying he should buy his own tubes and learn to patch them is a little inconsiderate, I’m buying them because I work in town and he doesn’t, and he’s not as confident at patching as other cyclists maybe simply because he hasn’t been Cycling for as long as other people, I think it’s worth remembering that other people might not be as confident or skilled at these things because they haven’t been doing it as long, hence the question about tubes.
    – Abbie Davy-Cripwell
    Mar 29, 2019 at 16:11
  • @AbbieDavy-Cripwell Fair enough. Patching is a skill worth learning, it needs practice and a good method is all.
    – Criggie ♦
    Mar 29, 2019 at 18:44
  • @AbbieDavy-Cripwell no offense meant
    – Argenti Apparatus
    Mar 29, 2019 at 18:45
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    Consider buying two tubes. Punctures are inevitable, changing the tube may be easier than patching it on the road or trailside. While picking up the tubes inquire about basic maintenance classes. Many shops offer them free.
    – mikes
    Mar 29, 2019 at 21:56
  • If you're going to get a patch kit, you should also get it from your local bike shop. Don't cheap out and buy the garbage they sell at Walmart. It's hardly capable of getting your punctured tube to the next bike shop. Patches from bike shop patch kits can get you halfway across the country. At least that was my experience.
    – Michael Hampton
    Mar 30, 2019 at 4:19
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Any 700c tube with "25" in the range would fit - assuming the valve stem is long enough.

Deep-rim aerodynamic wheels require longer stems than older-style box-rim wheels do.

A 700 x 18-23c would probably work fine, especially if the tire is a "small" 25. Bicycle tire and tube sizing is a bit of a crapshoot - one manufacturer's "25" can be a a mm or two larger or smaller than another manufacturer's "25". That can be significant for clearance and tube fit. And tubes are more than a bit flexible - obviously.

Flats are also an expected problem, especially with racing-type bicycles. Almost everyone riding such a bicycle rides with a tool kit that can fix at least one flat tire. Such a kit usually includes a spare tube - or two. Because flats happen, and no one wants to have to patch a tube in the rain.

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    Thank you for your response, it’s helped a bit, Thank you for being a little bit more kind in regards to BF not knowing how to repair it himself, I’ve suggested we get him a patch kit, I’m going to put it together myself for him, I’ve found some good stuff, his birthdays coming up so I’m think early birthday present 🤫
    – Abbie Davy-Cripwell
    Mar 29, 2019 at 16:22
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I think you have the hang of the 25 needing to fit into the range of numbers on the inner tube. These numbers refer to millimetres, the width of the tyre, and tubes can be stretched within reason to suit a few different sizes of tyre.

You're right that the 700 x 35-38 tube is way too big. If you chose that one, it would be unnecessarily heavy and the bagginess of the tube would make it more susceptible to getting pinched when the tyre gets mounted. Putting a hole in the replacement tube is never fun.

Now the 700 x 18-23 tube is a marginal case. This time, the tube will be stretching up to and just beyond the size it is designed for, by 2 mm. There is a difference of opinion on whether this is a problem or not. There was even a semi-recent question on this site about whether a tube should be used at the low or the top end of its range and lets just say there are arguments for either case (cyclists can rarely agree on anything). I would certainly use one of these if I didn't have an alternative but I would prefer to have an 18-25 tube so that it wouldn't even need thinking about.

By using an 18-23 or 18-25, when you put a little air in to install the tube, it takes its size and shape without any bagginess and stays out of the way a little better when you mount the tyre.

So yes, it would be best if there was a 25 in the size range of the tube and 700 x 18-25 tubes do exist quite readily if you can track down a shop with them in stock. 18-28 would also be just fine of course.

TL;DR I think you're on the right path, just facing a bit of doubt because you haven't found them in stock yet. That said, 25 mm tyres are very common on road bikes so I’d expect most bike shops to stock a compatible tube, keep looking and don’t be afraid to ask shop staff to direct you or dig one out from the stock room.

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  • I found the other question, but could be a pandora's box >< bicycles.stackexchange.com/questions/56156/…
    – Swifty
    Mar 29, 2019 at 17:56
  • I once used a tube that was "too small" for my tire. It lasted about 50 miles. I don't think I'll do that again except in extraordinary circumstances, like being in the middle of nowhere and getting two flats in an hour.
    – Michael Hampton
    Mar 30, 2019 at 4:23
  • I changed a 18-23 tube with a 20-25 (I think) one - and lo and behold, they were the same size to my untrained eye.
    – Calin Ceteras
    Apr 1, 2019 at 9:58
  • I'm replacing a tube for 24" 1.5 tire (40-507 really 1.5748"). There's not much choice available at that size but there are plenty available pre-slimed at 24 X 1.75-2.125. Is it possible to use a larger tube?
    – Olsonist
    Jul 29, 2020 at 0:47
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A 700 x 18-23c will fit on a 700 x 25c. I got a 700 x 25c tire, and just had my first puncture on my new road bike last week. Stock inner tube is 700 x 18-23c.

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