Wheel sizes

Discussion in 'Bicycle Mechanics and Repairs' started by nigelb, 9 Apr 2010.

  1. nigelb

    nigelb New Member


    What is it with wheel sizes?

    How do I measure what size a wheel is?

    Just measured what I thought was a 700, and its 25" diameter, or about 630mm?

  2. ianrauk

    ianrauk Tattooed Beat Messiah

    Atop a Ti
    Here is an excellent article by Sheldon Brown explaining in detail the different wheel/tyre sizes.
  3. OP

    nigelb New Member

    Thanks, having had a look, I start to understand why I was confused!

    My problem ...

    I've bought a 2nd hand cheap hibred (bad mistake), been fixing stuff, but had an event today.

    Before I set off, I checked the tyres, say 65PSI max, so I pumped them up to 60 psi (previously not had them much above 50 psi).

    Noticed a sudden bang at one stage, but couldn't see what it was, so ignored it.

    Cycling home this evening, life started to get rather hard.

    Eventually ground to a halt, wheeled the bike to somewhere to stop, and had a look.
    The tyre seemed to have floated off the rim for a significant portion of the wheel (like more than half).
    Brakes blocks were jamming on the tyres.
    I figured maybe excess pressure was causing a problem, and let a bit out (didn't want to let too much out, didn't have a pump).

    Was then contemplating what to do next, suddenly a huge BANG, inner tube had split (not out through the tyre, mind).

    Taking the back wheel off whilst waiting for my lift home, I found :-

    5 broken spokes!
    A rather non-straight wheel (what a surprise)
    A tyre which seems too large for the rim - slides on and off easily.
    Rim measures up as a 700c, and the tyre is 700x35cl, Schwalbe Marathon Plus.

    I'm very confused.

    Have a possible donor bike ("racer" with a broken frame) half tempted to move wheels and gears, etc over, but I suspect it isn't that simple?

    Well, at least I didn't fall off :-)

  4. PpPete

    PpPete Guru

    Chandler's Ford
    Me too. Those tyres have a reputation for being hard to get on and off.
    Is the rim "hooked" or one of those old school ones with flat sides (on the inner surface) Or is the tyre bead broken?
  5. OP

    nigelb New Member

    Right, tyre is fine, just I hadn't seated it evenly on the rim.
    (talking to the lbs, its a common problem)

    Having got the whole tyre back on, it makes sense (and the fit does seem reasonable when you have both beads over the rim - oops).

    Still, rear wheel needs rebuilding at the very least, may well need a new one.
    Its 6 speed, shifter is 7 speed, front wheel is also slightly buckled, pedals cracked and failing (awaiting a delivery from Wiggle) and occasional clicking from the bottom bracket.

    Time to move on, I'll try a rebuild with the "bits" from my garage but visited the lbs with a view to "Cycle to work" ;-)

    Dawes Tanami looks like the beast, only problem is lbs price is £449.99, online is £335 (inc delivery)! Will see if the online will do the scheme, then prob go and spend £100 at the lbs on accessories - I appreciated their help, but that's a large price difference!

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