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Tyre Sizes

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  • 15-05-2012 8:21pm
    #1
    Slappy101
    Closed Accounts Posts: 10 ✭


    Hey,

    I just got a new bike (felt qx65), and was checking out the wheels.

    I don't know much about the numbers so I was hoping somebody could explain them to me.

    On the tyre itself it says 37-622 (700 x 37c - 28 x 1 5/8 x 1 3/8) and on the rim it says ETRTO 622 x 19 A-MI. Is it normal that the tyres and rims are different sizes? Thanks !
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    #2
    dubmess
    Registered Users Posts: 282 ✭✭dubmess


    They are the same size, the 622 is the important bit, it refers to the 'bead seat diameter': From the hallowed mouth of Sheldon Brown:

    "The Bead Seat Diameter (B.S.D.) is the crucial dimension that determines whether a particular tire can fit onto a particular rim. It specifically refers to the "shelf"-like area inside the rim where the tire's bead sits.
    The Bead Seat Diameter is the fundamental dimension used in the ISO/E.T.R.T.O. system of tire and rim sizing. This is the great virtue of that system, compared to all of the older systems that referred to the tire's outside diameter, with no specific reference to rim diameter or to the rim/tire interface."

    If you fancy finding out more check out his full article here:
    http://sheldonbrown.com/tire-sizing.html


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    #3
    Slappy101
    Closed Accounts Posts: 10 ✭Slappy101


    dubmess wrote: »
    They are the same size, the 622 is the important bit, it refers to the 'bead seat diameter': From the hallowed mouth of Sheldon Brown:

    "The Bead Seat Diameter (B.S.D.) is the crucial dimension that determines whether a particular tire can fit onto a particular rim. It specifically refers to the "shelf"-like area inside the rim where the tire's bead sits.
    The Bead Seat Diameter is the fundamental dimension used in the ISO/E.T.R.T.O. system of tire and rim sizing. This is the great virtue of that system, compared to all of the older systems that referred to the tire's outside diameter, with no specific reference to rim diameter or to the rim/tire interface."

    If you fancy finding out more check out his full article here:
    http://sheldonbrown.com/tire-sizing.html

    Ah thanks for explaining man, I was reading that earlier but got a touch confused because the rim and wheel had different measurements.

    So does that mean I can buy any 700/622 size tyre and it will fit comfortably on the rim???


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    #4
    dubmess
    Registered Users Posts: 282 ✭✭dubmess


    Slappy101 wrote: »
    Ah thanks for explaining man, I was reading that earlier but got a touch confused because the rim and wheel had different measurements.

    So does that mean I can buy any 700/622 size tyre and it will fit comfortably on the rim???

    To a certain extent it does, the 37 indicates the width of your tyre, so if the bike came with that it would probably have a fairly wide rim as it's meant for commuting/touring. You could go up a bit in size and down a bit in size without altering how the tyre performs.

    I'm by no means an expert, but if you go too large I believe the tyre can end up being sloppy and possibly rolling off the rim under pressure, too narrow and you'll be losing the profile of the tyre, also possibly affecting handling.

    There's a chart way down the end of that article entitled 'width considerations' which deals with that. You may have to get out your calipers and measure the width of your rim if you want to get really nerdy about it :)

    I'd imagine you could go up to a 45 and down to a 28 no problem, after that I couldn't tell you what might happen!


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    #5
    Slappy101
    Closed Accounts Posts: 10 ✭Slappy101


    dubmess wrote: »
    To a certain extent it does, the 37 indicates the width of your tyre, so if the bike came with that it would probably have a fairly wide rim as it's meant for commuting/touring. You could go up a bit in size and down a bit in size without altering how the tyre performs.

    I'm by no means an expert, but if you go too large I believe the tyre can end up being sloppy and possibly rolling off the rim under pressure, too narrow and you'll be losing the profile of the tyre, also possibly affecting handling.

    There's a chart way down the end of that article entitled 'width considerations' which deals with that. You may have to get out your calipers and measure the width of your rim if you want to get really nerdy about it :)

    I'd imagine you could go up to a 45 and down to a 28 no problem, after that I couldn't tell you what might happen!

    Thanks for clearing that up, might invest in some puncture resistant tyres now that I know the score !


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