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On 28 Jun 2005 at 7:53, Neil wrote: > >From: Jim Adney [mailto:jadney@vwtype3.org] > > > >If my old rule of thumb works in this range, then a 185/70 should be just > >about the same diameter as a 165. 205/60s should be also. > > Hey Jim, with computers and the internet, you don't have to use you thumbs > anymore. Some Miata enthusiasts have taken all the work out of things by > making a "Tire Calculator". Check it out here: > http://www.miata.net/garage/tirecalc.html > > Looks like your old thumb is still pretty accurate though :~) Nice site, thanks! My rule of thumb is that a width increase of 20 (like 165 to 185) can be compensated by a profile decrease of 10%. It's not perfect, however, so the web site helps a lot here. It's also worth mentioning that different model tires of one stated size will still vary in actual size, so a calculator like this can't be completely accurate. I've got an old Michelin booklet that goes thru all their tire models and sizes. For each model and size, they give radius, effective rolling radius, rev per mile, rev per kilometer, and a few other things. I found it interesting that not all Michelin 197/70-15 (for example) tires would have the same rev per mile. -- Jim Adney jadney@vwtype3.org Madison, WI 53711-3054 USA ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ List info at http://www.vwtype3.org/list | mailto:gregm@vwtype3.org ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~