Tyre Height?

jimcameron
jimcameron Posts: 199
edited July 2011 in Workshop
I'm probably being a bit special here but is there a way to work out tyre height from tyre width. Say a 700c x 23 tyre - tyre width is 23mm. I know 700c corresponds to the circumference, but is that the circumference of the outside rolling edge of the tyre or is that the rim circumference?

Cheers Jim

Comments

  • jimcameron
    jimcameron Posts: 199
    jesus i mean diameter not circumference..
  • jimcameron
    jimcameron Posts: 199
    i think what i'm trying to say is - is a 700 x 35 c tyre taller than a 700 x 25c tyre or is it just wider?
  • mz__jo
    mz__jo Posts: 398
    The 700C is a nominal size which should give a diameter of 700mm with a C section tyre which should be 39mm high if my maths is correct. The rim diameter is 622mm. Wheels that are not fitted with a C section tyre but are on a 622mm rim will not have a diameter of 700.
    Once upon a time 700C had some significance as a dimension, nowadays people tend to refer to anything mounted on a 622mm rim as a 700 wheel.
    The business is even more complicated by the 29er size on mtbs which also uses a 622mm rim but with a tyre much bigger than a C section therefore a diameter much bigger than 700mm.
    There have been posts on this subject in the special interests section of this forum. Also Sheldon Brown's site explains it pretty well.
    The ISO system for bicycle tyres uses the rim diameter and the tyre section. I can't remember which goes first but I think it's the tyre section so 700Cx23 would become 23x622 (someone correct me if that is not the right order)
    http://rctl.ffct.org/
  • crankycrank
    crankycrank Posts: 1,830
    Yes, a wider tyre will have a greater dia/circumference. Each brand and model will probably have slightly varying dia between their labeled size as well so it can get a bit tricky if clearance is an issue.
  • mz__jo
    mz__jo Posts: 398
    crankycrank wrote:
    Yes, a wider tyre will have a greater dia/circumference. Each brand and model will probably have slightly varying dia between their labeled size as well so it can get a bit tricky if clearance is an issue.

    Quoted dimensions vary (sometimes a lot) from real dimensions. Michelin dimensions tend to be very generous, asiatic dimensions tend to be quite tight. A Kenda 28 must be about equivalent to a Michelin 25. The rim width also makes a big difference to tyre height/profile. There is only one safe way to know -mount your chosen combination, inflate to proposed riding pressure (that makes a difference as well) and measure (in my case for cycle computers I measure the development over three revolutions to try to be a bit more accurate). Makers quote dimensions but not always the rim that they use for the calculation.

    There is probably an approved ISO testing procedure but I haven't a clue what it is.
    http://rctl.ffct.org/

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