Re: [CR]Requested Clarification: 700C & 27" / wheel & tire sizes / framefit -- sorta for the less-experienced

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Date: Tue, 25 May 2004 18:17:15 -0400
To: "" <>,
From: Sheldon Brown <>
Subject: Re: [CR]Requested Clarification: 700C & 27" / wheel & tire sizes / framefit -- sorta for the less-experienced wrote:
>Mr Collins wrote:
><Could someone clarify for me the basic distinctions between 27" and 700c
>wheels? It seemed that in the discussions about 27" sew ups, there was
>overlap. Might 700c wheels fit bikes made for 27" and vice-versa? I always
>thought that to be impossible.

That's generally so with older frames, there's only a 4 mm difference in radius (700c is smaller.) Newer, tight-clearance road frames won't handle 27 inch wheels, but any frame that will work with 27s will also take 700c, but you may have trouble getting the brakes to reach down low enough.
>Okay now, onward to the heart of the matter: I recommend checking
>into Sheldon Brown's website for a thorough discussion of wheel and
>tire sizing. He's been there and done that.

Thanckx! is the place.
>A very precise way to consider tire and wheel size is to measure the
>diameter of the "bead seat area"--where you'd stick the glue if
>you're considering a rim for tubulars, or literally where the bead
>goes for a "wired-on" (clincher) tire. The imprecise, shorthand way,
>popular over the years (check into 1950s UK cycling magazine ads)
>was to speak of the nominal outside diameter. In reference to
>lightweights, one would speak of 27" sprints (i.e. 700C tubulars,
>because the outside diameter of a 700C tire and wheel is about 27"),
>and 28" which meant 27 x 1 1/4 clinchers--28" being the nominal
>outside diameter.

I think this is not correct. There are two sizes that I know of being called "28 inch":

1. The 635 mm size, used on rod-brake roadsters, typically marked "28 x 1 1/2"

B. The 622 mm size, most commonly known in English speaking countries by it's French designation "700C" is commonly called "28 inch" in northern Europe. This is commonly designated with two fractions, as in: "28 x 1 5/8 x 1 1/4."

I have never known of anybody calling the 630 size "28 inch" and I've never heard of a tire in this bead seat that was anywhere near that large an outside diameter. (The 622 size, though the rim is smaller, exists in a much wider range of widths, up to 47 mm, which is close to 28 inches at the tread.)

Sheldon "Ti/yres" Brown Newtonville, Massachusetts +-------------------------------------------+ | If Stupidity got us into this mess, | | then why can't it get us out? | | -- Will Rogers | +-------------------------------------------+ --
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