On Sat, 12 Jul 1997 12:01:28 EDT britcars@juno.com writes:
>
SNIPPY-SNIP
>Be aware, however, some tire brands are sized differently even though
>nominally the same! We now have two cars in the shop on 175R14s. The
>tread width of my Michelins is 5-1/2". Another B is on Winston 160
>tires; their tread is 6" wide and the tires look much bigger. The same
>holds true for different brands in 185 sizes.
>
>Lawrie
>British Sportscar Cente
It is very possible that two tires from different mfg. will have a
different tread width on the same nominally sized tire. For a very
simple reason. The tire size has nothing to do with tread width.
The 175 (or 185 or 165 or whatever) refers to the tire's maximum cross
section when mounted on the rim width for which it is designed. When
that tire is installed on a wheel with a larger or smaller rim width, the
cross section will vary, too. A good number to go by is for every 1/2"
change in rim width (smaller or larger), the cross section will change by
about .2" (5mm). Thus if you take a say, 185 tire that was sized based on
a 5" rim width and mount it on a 51/2" rim, it will actually be closer to
190mm wide. (but the tread width doesn't change). Usually your friendly
local tire dealer can provide you with charts showing which size tires
were "sized" on which rim width, and the range of rim widths allowable
for that given size.
For a fuller discussion on tire sizes and rim width, see "How to make
your car Handle", by Fred Puhn.
Rick Morrison
72 MGBGT
74 Midget
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