Tyre sizes - Triathlon Week

08-23-2004, 07:09 PM

Can someone explain what the two measurements in a tyre size represent and
what would be the difference between the following?

(Diameter x Width? measured where?)
700x20c
700x25c
700x23c

I'm a newbie when it comes to road bikes.

Thanks,
Brad

08-23-2004, 07:09 PM

Brad Hubbard <not.real@of.course> wrote:

>Can someone explain what the two measurements in a tyre size represent and
>what would be the difference between the following?
>
>(Diameter x Width? measured where?)
>700x20c
>700x25c
>700x23c

The "700" refers to the outside diameter of the rim (which is actually
622mm) and the tire. Obviously this isn't really exactly 700mm unless
you're running 39mm tires. It's an archaic standard that doesn't
really mean anything any more. In fact, there were several different
700 standards (the one that "stuck" being the 700c standard).

The diameter is normally measured across the widest part of the
mounted and inflated tire. However, the width of the rim affects this
measurement, and tire companies are all over the place in
manufacturing tires of a given "size". For example, some 25mm tires
are actually 23mm or less (a common ploy since it makes your "25mm
tire" look lighter than your competitors "real" 25mm tire).

Mark Hickey
Habanero Cycles
[Only registered and activated users can see links. ]
Home of the $695 ti frame

08-23-2004, 07:09 PM

Mark Hickey wrote:
> The "700" refers to the outside diameter of the rim (which is actually
> 622mm) and the tire. Obviously this isn't really exactly 700mm unless
> you're running 39mm tires. It's an archaic standard that doesn't
> really mean anything any more. In fact, there were several different
> 700 standards (the one that "stuck" being the 700c standard).

Thanks Mark,

That helps.

Cheers,
Brad