Isn't it funny how this comes up every couple of years :-) When manufacturers initiate a confusing situation, that confusion is bound to endure. In any event, here's the answer (from the archives) I supplied the last time this came up:
http://search.bikelist.org/
In the email found at the above link, there is a link to the Continental Web site. If you go to that Web page and examine the specifications they provide for tubulars, you will find that (for reasons only Continental's marketing people can explain) the same sized tubulars use the designation 700, 28" and 27" at different places in their catalogue.
In a way, it's pretty funny...
Fred Rednor - Arlington, Virginia (USA)
> I am sorry to correct you that
> tubulars are not sized 700C (note the cap C rather than
> lower case c, they are not 700cm in diameter!) - 700C is the
> equivalent size in clincher rims/tyres. Tubulars can be
> called 700 or 28in.
>
> The 700C tyre size comes from the French; in the rest of
> Europe the size is referred to as 28 x 1 5/8in or 28 x 1
> 3/4in with a 622mm bead diameter though normally these days
> they are simply referred to as 28s. The only other 28in size
> likely to be encountered unless you are into truely old
> bikes is 28 x 1 1/2in (called by the French 700B) and with a
> bead seat diameter of 635mm.
>
> At one time (100 or more years ago) there were other 700
> sized tubulars but this 700 size has prevailed. It is not
> quite as straightforward with 26in tubulars - they do seem
> to be made to two different standards one equivalent to the
> 650C clincher size (bsd of 571mm) (in the UK some carrier
> trades bikes use 650C tyres but with 1 3/4in cross section
> and this is the original cross section for this bsd) and
> some equivalent to the 650B clincher size (bsd of 584mm) -
> in practice most 26in tubulars will fit on most rims but
> they are often horribly tight... And almost no tyre seller
> will know which size of 26in tubular they manufacture...
>
> The French used the A, B, C suffixes to denote the nominal
> cross section of tyre. A equalled 1 3/8in, B 1 1/2in, C 1
> 3/4in, no suffix was the equivalent on 1 1/4in and all sizes
> of French rims 350, 400, 450, 500, 550, 600, 650, 700 were
> at one time available in no suffix, A suffix, B suffix, C
> suffix cross sections.
>
> The number 450, 700 etc was the nominal size of the wheel
> when fitted with a tyre of the correct cross-section. Hence
> 700C rims have a smaller diameter than 700B which has a
> smaller diameter than 700A. Most of the sizes are long
> obsolete... The same applies with the inch sizes 28in refers
> to the nominal overall diameter of the wheel when fitted
> with correct cross section tyre. Hence 28 x 1 3/4in rims are
> smaller than 28 x 1 1/2in rims...
>
> Most of the rest of Europe used inch tyre sizes equivalent
> to the French sizes - the notable exceptions are Scandinavia
> and some parts of Eastern Europe... The Scandinavians in
> particular used a whole lot of peculiar tyre sizes which
> were not even common across the region...
>
> Fortunately these days most countries use 700C or 28in
> tyres and most also use the 26in MTB size (559mm bsd) which
> is a US based tyre size.
>
> The old 27 x 1 1/4in size does not fit into any of the
> systems; it was invented by Dunlop in 1935 and was I am sure
> designed to be unique so that in the early years Dunlop was
> the sole supplier of tyres for that size rim which has a bsd
> of 630mm.
>
> Hilary Stone, Bristol, British Isles
>
> FujiFish1@aol.com wrote:
> > Hey Tom,
> > Hope all is well in health and family.
> > Tubulars for a standard sized road bike are
> simply 700c. I think I read in the past, here on
> the CR list, that the 28" denotation was something
> that came around in Europe in answer to our US 27"
> sizing parameters. Don't really know if they are
> bigger, smaller, or what ... because all I've ever
> needed to know is that "standard" tubular tires fit
> standard 700c tubular rims. All my tubular rims are
> 700c, as normal, and I've never failed in applying any
> tire to any of them, in terms of size and fit.
> You can acquire smaller tubular tires for smaller rims, but
> the difference will be strikingly obvious next to a
> 700c.
> > Ciao,
> > Mark Agree
> > - riding his 28" or 700c tubular tires on the same
> bike - Southfield MI USA
> > ~ ~ ~
> > Date: Sun, 24 May 2009 12:27:36
> -0400
> > From: Tom Sanders <tesanders@comcast.net>
> > Subject: [CR] Sizing question for tubular rims
> > To: _Classicrendezvous@bikelist.org_
> (mailto:Classicrendezvous@bikelist.org)
>
> > I recently got a set of gorgeous wheels with
> Tipo HF hubs and NISI tubular
> > rims. There is no indicator at all of
> sizing. I measured them and they
> > actually seen a hair larger than the 27" wheels
> on my Paramounts. They came
> > off a Raleigh, so the person who sold them tells
> me. I believe I have heard
> > that all tubular are 28", but I have also heard
> that they are all 27". I
> > never gave it much though before, they are
> spaced at 120 so this gives an
> > indication of the era. Could these be 28"
> rims? Measuring seems a bit iffy
> > because of the different height of rim walls,
> does one measure to the inside
> > edge of the rim? If so to the outboard
> edge? Some are concave, of course
> > which seems to muddy the water even more.
> >
> > Sounds pretty basic, but I don't think I've ever
> encountered such a thing
> > before. I'm also thinking that
> Raleighs of that period used inches, but the
> > rest of Europe was using 700c by then, right?
> >
> > Tom Sanders