Conference noted::bicycle

I'm not *too* sure why 700 wheels are called that. The diameter of wheel
plus tyre is pretty close to 700mm.

As for tyres and your 640-40 question: this pair of numbers is the most
important one to know for sizing a tyre. The first number is the bead 
diameter, that is, the diameter of the wire stiffener of the tyre. This
*must* be identical to the rim diameter of the intended wheel. This 640 
you quote is quite big, it must be a tyre for a 28 inch wheel. Tyres to fit 
700 wheels have a bead diameter of 622, and tyres for 27 inch have a bead 
of 630.

The second number is the tyre width. 40 (mm) is wide, about 1.6 inches, so
your example tyre is obviously built more for comfort than sport. Tyre
widths are much more nominal than bead diameters, tyres with the same
stated width from different manufacturers can vary widely in actual width.
Then again, it's not a critical dimension in getting a tyre to fit a rim,
unlike the bead diameter.


Rod

    Quite so, Rod.  I believe the "700" is the nominal finished size - it
    seems pretty evident that a 700 x 20 will be thinner all round than a
    700 x 35, and therefore a smaller overall diameter.  700 also
    corresponds roughly to the old 27" of the British system.  As for the
    "C", I'm pretty sure that this is the "crotchet" style of the rim
    section made for the current narrow section covers.  Real cyclos in
    France (may eat Quiche) but must use 650B which I believe is the old 26"
    style where the cover was held on entirely by the wires.

    	700 - is this the size of tubular (sew-up) rims, perhaps?
    
    	Tubular rims are only available in one size, in general. There
    	are most likely other sizes in manufacture though.  There does
    	not seem to be a large market in the U.S. for other sizes/uses
    	than the traditional "700".
    
    	Hmmm, I wonder, does the "c" in 700c stand for "clincher"?
    	Ahhhhhhh, I doubt it...
    
    	Remember when clinchers were 27" wheels, and sew-ups were just
    	slightly smaller in diameter? Making it very difficult to swap
    	racing sew-ups with touring clinchers?
    
    	Then this thing called the 700c clincher was made available to
    	the public.  The big sell was that they were the same diameter
    	as tubular rims, allowing one to exchange wheelsets without re-
    	adjusting your brake pads to fit. They also started using that
    	strange french dohicky, the presta valve. What? A presta valve
    	on a clincher rim? Nahhhhhh...
    
    	Hmmmmm...
    	Remember Campy nuovo record long reach brakesets?
    
    	Were you a bike-buff back in the seventies?
    	Shhhhhh, don't tell anyone...

    To he** with the 70's....
    
    Titan bars and stems
    Mansfield Bath Road saddles
    Dunlop 0's
    Simplex rod-operated front changers
    Holdsworth's Aids - better value than the other kind!
    Cycling - price 4d
    Mrs Smithers' racing digs at Burden
    
    This IS the nostalgia note, isn't it???
    

Dear .0, I must apologise for the behaviour of my fellow-noters in .3 and
.4. When they reach a certain age, it takes very little to set them off, you
know. Just be understanding and bear with them.


Rod

	Not too long ago, Bicycling magazine had an explanation of what 
	700c means.  Of course, I can't remember it off the top of my 
	head....

    It went something like this, "700" is the nominal outside measure
    of the tire when mounted on the rim and inflated.  700c is the
    only one commonly available in the US and is compatible with
    the commonly available (alomst 27")  tubulars.  700b and 700a
    are for slightly smaller diameters rims one which are mounted
    somewhat heavier tires (tyres!) which then have the same nominal
    outside diameter.
    
    Through miracles of standardization which can only be achieved
    in the bicycle industry in the USA, ATB 26" rims are 600a
    while the "small front wheel 26" rim" is 650c, or is it 650a
    and 600c, respectively, oh never mind, pretend you never read this.
    
    ed