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As we see from the picture
above, there are different sized rims found on bikes today. Some of
the rims have the same English Standard of Measurement yet differ in
the Metric Standard.
The English Standard such as 20" or 26" is meant to show
that if a tire was on the rim and fully inflated, then the diameter of
the tire would be 20 or 26 inches tall. This is not always the case
and has often led to confusion over which tire to order. Please follow
the instructions at our sizing section to get a good fit.
The Metric Standard measurements like the 406 or 559 is known as ETRTO
or ISO. These were attempts at the standardization of rims and is
really the only sure way of properly matching the diameter of the rim
to the diameter of the tire. Again this is not necessary if you use
our calculator at our sizing section.
Bead Seat:
The approximate diameter of the rim (not tire) in millimeters. This is
the area in which a rubber tire would rest inside of the rim. Rims are
always a little bit bigger than the bead seat as the bead seat is more
accurately measured by one half of the height of the rim wall to the
other side of the rim one half of the rim wall. For example the
20" (406) rim is actually 422 mm (+or - 2mm) in diameter. So the rim walls
are 16mm in height. Subtract 8mm from either end and measure the
difference and you have 406mm.
Hook Beads:
The little metal hook like devices found inside of the rim at the top
of the rim where a rubber tire would hook itself to. We use these also
to fit airless tires to rims and the width of the rim is very
important to determine if our tire can squeeze into it.
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Bicycle Tire Sizes:
The chart below shows all the sizes made in the last 15 years with
the ISO equivalents. Yes there are tire sizes that aren't on the list
because this list only includes those sizes of tires that were on a
bicycle when it left the factory. Our list doesn't include any
aftermarket tires Please let us know if any information is inaccurate.
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