Re: [CR]27x1.25 NOT tyres for Dunlop Rims

In-Reply-To: <785545.45086.qm@web44904.mail.sp1.yahoo.com>
References: <785545.45086.qm@web44904.mail.sp1.yahoo.com>
Date: Thu, 20 Dec 2007 20:40:59 -0500
To: Norris Lockley <norris.lockley@yahoo.com>, classicrendezvous@bikelist.org
From: "Sheldon Brown" <CaptBike@sheldonbrown.com>
Subject: Re: [CR]27x1.25 NOT tyres for Dunlop Rims

I have to respond to this incorrect Subject: heading.

It is always wrong to translate tire/tyre sizes between fractions and decimals.

http://sheldonbrown.com/tire-sizing.html#fractiondecimal

"Brown's Law of Tire Sizing:

If two tires are marked with sizes that are mathematically equal, but one is expressed as a decimal and the other as a fraction, these two tires will not be interchangeable."

As it happens, there are no decimally-designated 27" sizes, but it's still a very dangerous habit.

For instance, 26 x 1.75 is ISO 559 mm, while 26 x 1 3/4 is ISO 571 mm.

26 x 1 1/2 is ISO 584, but 26 x 1.5 is ISO 559

16 x 1.5 is ISO 305 but 16 x 1 1/2 is ISO 349

...and so on...

Sheldon "It's Not Arithmetic" Brown --
    Harris Cyclery, West Newton, Massachusetts
       Phone 617-244-9772 FAX 617-244-1041
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