tire size(do the math)

[Alfanovice@domain.elided]

When changing rim size you want to keep the overall diameter of the tire/rim 
combination as close to the original as possible.  Tires are sized using 
width in millimeters and aspect ratio expressed as a percentage of this width 
for heighth.  So, you must convert wheel size to millimeters to find the 
overall diameter.
One inch equals 25.4 millimeters.  Therefore a 14 inch rim is a 355.6mm rim.  
A 185/70 tire is figured as (185x.70)x2 since you have to account for both 
sides of the tire on the diameter, or 259mm.  Adding this to 355.6mm gives 
you 614.6mm, which is the overall diameter for a 185/70 tire on a 14 inch 
rim.  This is the closest to the original size of the old 165 metric that 
came on the 1971 Spider.  The old size had an aspect ratio of 80 percent, for 
information's sake.
To spell it out, the formula is:
(Rim size in inches x 25.4) + (tire width x percentage of this width x 2).
Simply use this formula to determine which tire and rim size you feel most 
comfortable with when deviating from stock.
Brian Ancelin
--
to be removed from alfa, see /bin/digest-subs.cgi
or email "unsubscribe alfa" to majordomo@domain.elided