Michael Maskalans <dml@tepidcola.com> wrote:
: On Sat, 30 Sep 2006 jon@dakota-truck.net wrote:
:>
:> Hmm, it just occured to me that maybe you were asking what
:> would the metric equivalent of a 32x11.50 on a 17" rim, in
:> which case the answer is 292/65 R17. Of course, no such tire
:> exists, but a 290/65 R17 or 295/65 R17 would be very close
:> (assuming of course that those tires exist.) :-)
:>
: Just also keep in mind that the measurements on the side of the tire
: (whether metric or inch measures) do not exactly match the tire size.
: There are good odds that a 295/65r17 would NOT measure 32x11.5, it may be
: more like 32.5x11.5 or 32x12....
: Check the tire manufacturer's site for an info sheet on the tire model(s)
: you are looking at, they will list actual dimensions (tread width, overall
: width on a particular rim, and either static radius or overall diameter).
: Go by those dimensions, they are accurate. You can see just how wrong the
: sidewall numbers are if you start plugging things into the calculator and
: comparing reality to sidewall numbers.
That's a good point. Even when you buy a tire classified
under the "inch" system, a 33x12.5 might not actually be 33" tall
and 12.5" wide. It should be darn close, but it may not be right
on; there will always be varyations, and "fudging" by the manufacturers
(and their marketing departments). As Mike noted, even when you
know the actual dimensions of a tire, you can take that same tire and
mount it on a different rim and the section width will change. (The
wider the rim, the wider the tire, because the sidewalls will expand
out to the bead area of the rim, within reason.) A helpful rule of
thumb is that if the manufacturer lists the section width on a
particular width rim, and your rims are a different width, for
every 1/2" of rim width difference, add or subtract (as applicable)
about .2" of section width.
The tire calculators and such are very helpful to get you
close, but I definitely agree with Mike - double check the theoretical
dimensions against those given by the manufacturer for the exact
tire you are considering. (And even then, take them with a grain
of salt and leave yourself some margin of error.) The only way to
know for absolute certain the exact dimensions of a tire are to
mount it on the rim and put it on the vehicle. Of course, by that
point, usually you have purchased them already which is a little late
in the game to start taking measurements. :-)
--
-Jon-
.- Jon Steiger -- jon@dakota-truck.net or jon@jonsteiger.com -.
| '96 Kolb Firefly, '96 Suzuki Intruder, Miscellaneous Mopars |
`-------------------------------- http://www.jonsteiger.com --'
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