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Actual wheel size

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01 / Original postActual wheel sizeCarey · 18 Jul 2005 02 / This pagePosts 1–10Page 1 of 1 · chronological order 03 / Latest replyPost #10Tim · 19 Jul 2005

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rec.sport.unicycling
Published
18 July 2005
Last activity
19 July 2005
Original author
Carey
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10
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Topics
Frame sizingWide tyres

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  1. Original post
    Carey
    Archived post
    #1

    I need one of you experts to help me get the wheel sizes straight.

    I'll put down what I think and you can correct me.

    What we refer to as 20", 24", and 26" wheels and tires are generally
    measured at the outside diameter of the tire. The rims are
    significantly smaller in diameter. The 700c rim, however is a
    measurement of the rim without a tire.

    The 700c rim can be fitted with a tire that will make the outside
    diameter either 28" or 29" depending on the depth of the tire mounted.

    I have also heard that there is a British tire and wheel size that is a
    28" measured in the customary way of 20", 24", and 26"...but it is not
    on a 700c rim.

    I am looking at a 28"/29" unicycle for my next ride and want to be sure
    that I end up with a 700c rim which is a more universal size, but the
    rumor of the off-size 28" has me spooked when I look at the sales pages.
    Who uses those, if they in fact exist, because I don't want to get
    one.

    Thanks--this would all be nicer if we spoke of rim size versus tire
    size, like we do on cars, and most other rolling things.

    Carey

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  2. Tim
    Archived post
    #2
    Carey said:

    *What we refer to as 20", 24", and 26" wheels and tires are generally
    measured at the outside diameter of the tire. The rims are
    significantly smaller in diameter. The 700c rim, however is a
    measurement of the rim without a tire.*


    Those I know are the diameter from one side of the rim only to the
    other. The tire is not involved in the with the sizing. Like a 24 inch
    muni is really with a down hill 3 inch wide tire is more like 26 inch+.
    Tires are very different in sizes how tall they are it wouldnt make
    sence to size rims with the tires on them.

    I dont really know 700c rims. 28 inch would be 28 inch in diameter not
    as comon as 700c but more then 29 inch I believe but I'm not to sure.

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  3. James_Potter
    Archived post
    #3

    threadjackage....
    so a 19" trials uni has a 19" rim, right? and the tire is an extra like
    1-2 inches on both sides....
    so a 19" trials uni actually has like a 22-23 inch wheel, right?

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  4. loosejello
    Archived post
    #4

    Wrong. The trials is said to have a 19" rim because with the 2.5" tire,
    it is 20". With a 3" DH tire, bikers usually run a 26" rim and tire on
    the front, and a 24" rim and 3" tire on the back so they are the same. I
    think most rims are made so that with the standard size tire, 1.95",
    2.125" or whatever, makes it the listed size. My torker LX actually has
    a 16" or so rim. A trials rim is I think around 15".

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  5. Mikefule
    Archived post
    #5

    All tyre sizes are nominal, because the tyre section and pressure vary
    so much. Rim sizes are standard. So, you can buy a standard rim then
    fit any one of a number of different tyres to it.

    700c with a standard 32mm tyre on it gives a rolling diameter of almost
    exactly 28. With a fatter tyre, the rolling diameter is nearer to 29
    inches.

    700c = a nominal size of 70.0 centimetres.

    Old UK sizes included the 27 inch wheel (standard before 700c became
    popular) and the 28 inch wheel (already a bit of a curiosity even 20
    years ago).

    Tyres are not intercahngeable between different rim sizes.

    Therefore, in this size bracket, 700c is to be regarded as the standard.
    That's the size you'll get from a reputable supplier.

    Worry less.

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  6. leo
    Archived post
    #6
    Mikefule said:

    *Old UK sizes included the 27 inch wheel (standard before 700c became
    popular) and the 28 inch wheel (already a bit of a curiosity even 20
    years ago).*


    I had one Dawes bicycle with two 27" wheels.
    Try explaining everyone that 27" wheels are larger than 28" wheels.
    ....or try to find tires outside the UK for it!
    ...and so I had to lace new wheels when my tires needed to be replaced.

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  7. Jim
    Archived post
    #7

    Tire sizes are based on the outside measurement of the tire for lots of
    information see 'sheldon browns article'
    (http://www.sheldonbrown.com/tire-sizing.html)

    But all the 28" and 29" unicycles I have heard of (Kris Holm, Nimbus,
    Sun) have 700c rims which actually measure 622mm outside diameter

    my advice is to use the metric tire sizes e.g the 60-622 on the big
    apple 28x2.35" tire, the 622 is the diameter of the bead/rim in mm 60 is
    the width of the tires in mm

    I have a tire labelled 21x1 3/4" tire that has a 24"outside diameter.

    Old Schwinn were notorious for obscure tire sizes

    jim

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  8. Mikefule
    Archived post
    #8

    Back in my youth, I had bicycle with 26 x 1 3/8 tyres, which were
    noticeable large wheels than a 26 inch mountain bike/MUni wheel. Then I
    went onto 5 speed "racers" and 10 speed "racers" which as standard had
    27 x 1 1/4 tyres. Real hardnuts had
    27 x 1 1/8 tyres.

    I occasionaly saw bicycles with "28 inch" wheels. These were massive
    wheeled granny bikes - super dreadnoughts in the Dutch style.

    Around 1986 - 1990, I was heavily into bicycle touring and tandem
    touring, and I remember having to choose between 27 inch wheels or 700c
    wheels. As a bit of a conservative (small "c"😉 I went for the imperial
    size.

    We unicyclists only refer to 700c wheels as 28s or 29s because wheel
    diameter is critical to our sport, and easy to compare. Bicyclists
    would I suspect refer to 700c or "700c x 32mm" etc.

    The fact that a 700c wheel with a standard road tyre is almost exactly
    28 inches diameter is purely coincidental. There is no connection
    between what we refer to as 28s (700c x 32) and the old imperial 27s or
    28s.

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  9. johnfoss
    Archived post
    #9

    I've only seen a unicycle with an "old-school" 28" wheel once. That was
    in 1983. I'm pretty sure nobody makes them now, unless you order it from
    DM (in which case just ask to make sure).

    --
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  10. Tim
    Archived post
    #10
    loosejello said:

    *Wrong. The trials is said to have a 19" rim because with the 2.5"
    tire, it is 20". With a 3" DH tire, bikers usually run a 26" rim and
    tire on the front, and a 24" rim and 3" tire on the back so they are
    the same. I think most rims are made so that with the standard size
    tire, 1.95", 2.125" or whatever, makes it the listed size. My torker
    LX actually has a 16" or so rim. A trials rim is I think around 15". *


    Foot feel the warmth of the mouth. I think I understand now. So road
    tires are set up so that they end up having a 24" diameter but then Big
    DH tires are set up for that rim size also but they are likely more then
    24".

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