I have a road bike that has a flat tire, the rim is marked with the text

700Cx28/38c ETRTO 622x20

I am specifically looking at this Continental tube on Amazon. Under the sizing options there is an option

700 x 25-32cc

Which I think is the one that I want. The picture of the box (not necessarily correlated to my choice in sizing) has the text

20-622 > 25-630

Which again seems to confirm that this inner tube will be correct.

Will the tube size mentioned above fit the rim I describe? Or, should I select the size 32-42cc because the range on the rim (28/38c) has more #'s in the range 32-42 (6) than it does in the range 25-32 (5)?

I have been reading for a bit now and from what I understand the text on the rim (28/38cc) means that the tire (not tube) size that the rim will fit is between 28mm and 38mm. But what is confusing me here is the sizing of the tubes listed as that are listed as, for instance, 25-32cc. Does this mean the tube itself will fit on rims that can fit tires (not tubes) in the range of 25mm to 32mm?

In the end what exactly should I be looking for; what sizes of tubes will fit this rim properly?

I hate to "beg" for the answer seeing how much it is looked down upon on the stackexchange sites but I seem to actually be at a loss in understanding this correctly...

EDIT: Ok so I think I understand this much better now. My tire itself has the text 700x40c. Which means that the tire itself "prefers" a tube with a cross section of 40mm; moreover the tires cross sectional area is 40 mm!? So I can then buy any tube that says it will fit/(inflate to) a tire with a cross sectional area of 40c.

  • 2
    Tubes fit tyres and then tyres fit rims. There is no direct relationship between tube and rim. What is the sizing written on your tyre/tire ?
    – Criggie
    Jun 2, 2016 at 4:01
  • 1
    What is the size marked on the side of the TIRE?? Jun 2, 2016 at 11:41
  • @DanielRHicks ahh yes that makes more sense to list. It says 700x40c. Soooo I just want a tube that is listed as 700 x [# less than 40] / [# greater than 40]?
    – KDecker
    Jun 3, 2016 at 20:54
  • Correct. And even one that tops out at, say, 38 will probably do (though find one that "straddles" 40 if you can). Jun 3, 2016 at 21:45

1 Answer 1


It looks as though you're confused about the range of allowed tyres on the rim vs the tube. What connects the two is the size of the tyre you actually have.

There are two independent ranges. The rim is rated to take tyres in the range 28 to 38mm wide. Your tyre will be an exact size, and ideally should be within that range. You can measure the width or guess, because it's not critical.

That's because the tube will be rated to fit a range of tyre sizes. The one you're looking at will fit any time from 25mm to 32mm wide.

As long as the tyre you actually have is more or less the size of the tube, you'll be fine.

In practice a thinner tyre will be fine, it might just be hard to stuff all the tube into the tyre when fitting it (it's more obvious if you're trying to fit a 55mm wide tube into a 22mm wide tyre... and that example might not actually work because there will be so much rubber filling the tyre that you might not be able to get any air in).

The same applies to tyres, BTW. You could probably run 25mm or even 23mm tyres on that rim without problems, and likely 40mm or 45mm wide as well, if the tyre cleared your frame. I dont suggest you actually do run wildly out of spec tyres, but people do (I have run 55mm tyres on narrow rimes before).

Also, tyres fit a range of rim widths :) One guy I met ran narrow tyres on wide rims because he was convinced it lowered the rolling resistance. He may have been right, but it made hard cornering quite exciting when the rims hit the ground.

I suspect you're over-thinking this. It's straightforward once you understand it. (rim takes a range of tyres) + (tyre is one exact size size) + (tube fits a range of tyres).

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