My bike uses a tire size of 700x23/25C. I understand that the 700 indicates the diameter of the rim. 23 is supposed to be the width of the tread which I believe means 23 mm, am I right? So what does the 25c mean?

  • 2
    Possible duplicate of What does the "c" in bicycle tire size mean?
    – ojs
    Aug 29, 2017 at 17:22
  • 3
    @ojs nope - that's not a dupe because this is about two numbers for the tyre size, and not specifically about the c.
    – Criggie
    Aug 30, 2017 at 8:15
  • 1
    Can you tell us what manufacturer and model your current tire is, and perhaps include a picture of the size info printed or embossed on the sidewall? Aug 31, 2017 at 18:19
  • Keep in mind that 2mm is hardly measurable. You can't get a repeatable measurement more accurate than that, especially on different rims. Sep 1, 2017 at 12:13

1 Answer 1


Some manufacturers (e.g., Specialize) offer two width measurements (e.g., 700x23/25c) to indicate that the carcass is 25 mm wide, but that the tread patch is equivalent to a 23 mm tire. I believe this is done to create a more supple tire (larger volume tires can be run at a lower pressure) while reducing rolling resistance.

Another possibility could be to indicate width/height profile differences. A tire profile that is perfectly found tire will be the same in both. I don't know if any manufacturers are doing this.

  • 1
    Another possibility is that the actual width of a tyre in use depends on the width of the rim it is mounted on. I haven't come across a manufacturer labelling then with a range though.
    – armb
    Aug 31, 2017 at 16:41
  • @armb I think a hyphen would make more sense to indicate a range. Slashes usually indicates a duality.
    – Rider_X
    Aug 31, 2017 at 22:56

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