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19" vs. 20" tires

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  • 19" vs. 20" tires

    My son has a Koxx-One Uni.... stock tire says "20 x 2.5" On the Trials tires which are labeled 19" says the tires size is 20x2.5

    But they also have a section for 20/24 inch tires......... a bit confusing.

    So, my question is will the Creepy Crawler fit his rim?

  • #2
    The short answer is yes.

    The long answer: Trials rims are slightly smaller to accommodate larger tire volumes while still having the same outer diameter. On trials bicycles they put a larger volume tire on the back but a smaller volume tire on the front. What this means is that there are two different sizes of trials tires, usually labeled as front or back. Unicycles use the back size as it has more volume which gives more bounce. The ones that sell are the back size which is actually for a 19" rim even though the outside diameter matches a 20" tire. The easiest way to tell them apart is by the width, at least in the case of the creepy crawler the rear one is 20x2.5 while the front one is only 20x2.0. UDC puts trials tires in a category all their own because they are actually 19" rim and will not fit a standard 20" even though they are labeled as 20". It's confusing when you don't know what's going on but once you understand it's pretty simple.
    Last edited by Shmolagin; 2015-07-27, 04:39 PM.


    • #3
      Another way to make a clear difference of the two sizes is to use the ETRTO markings (european standard measurements).

      On the sidewall (or manufacturer website) you will find values line (XX-YYY) where XX is the width and YYY is the diameter.

      In short:

      19" (also labelled "Trial / 20") are 387mm in diameter

      20" (also labelled "Freestyle") are 406mm in diameter

      In case of doubt, you can have a look at the Tires section of the German site where all the tires are sorted by ETRTO diameter.
      => CrMo 29: KH XC rim, Nimbus CrMo hub, Spirit 110/137 & Schwalbe Big One
      => Flansberrium 26: Nextie rim, JumboJim 4.0, Spirit 127/150mm, M4O ISIS


      • #4
        Originally posted by Siddhartha Valmont View Post
        19" (also labelled "Trial / 20") are 387mm in diameter

        20" (also labelled "Freestyle") are 406mm in diameter
        Virtually EVERY model tire has a slightly different diameter, this can even vary a bit between two tires of the same brand and model.

        Yes it's confusing. Many trials tires are labeled 20"x 2.5"

        All (effective 19") trials tires are 2.5", 2.6", or 2.7" wide (most are 2.5"). I don't think I've ever seen a true 20" that had those widths. Look for something like 'Won't fit on regular 20" rims'.
        Ride everywhere and never just ride anywhere. If you can ride where you are going within a hour, do it, and if you can do a trick 50-75% of the time do it along the way.- Bob Burnquist

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