Jeff Liebermann wrote:

A 26x1.5 tire and a 26x1-1/2 tire are
different tire sizing systems:
http://www.sheldonbrown.com/tire-sizing.html
See charts of fractional and decimal sizes.

It says this [1], but doesn't explain how the
systems work what I can see. If you compare one
2x1.5 and a 26x1-1/2, why are they not
interchangeable, and what tire is wider?

In my experience the width is less important
than the diameter. One can make it work with
different widths. But perhaps that is different
in the road bike and MTB worlds?

BTW is this also a "different tire sizing
system"

37-622 28 x 15/8 x 13/8 700x35C
32-622 28 x 14/8 x 10/8

?

[1] Does Point Seven Five Equal Three Quarters?

Inch-based designations sometimes express the
width in a decimal (26 x 1.75) and sometimes as
a common fraction (26 x 1 3/4). This is the
most common cause of mismatches. Although these
size designations are mathematically equal,
they refer to different size tires, which are
NOT interchangeable. It is dangerous to
generalize when talking about tire sizing, but
I would confidently state the following:

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.

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