My calculator is just an excel formula. I got the tire sizes and revs-per-mile from several different tires sizes and manufacturers and found the actual 'average' rpm was about 96% of the calculated. 235/75x14 calculates to 27.878 inches diameter, so circumference is 87.581 inches. 63360 inches in a mile gives 723.44 rpm calc. divided by 96% gives 753.6 rpm actual. :) Ken Quoting Sandwich Maker <adh@xxxxxxxxxxxxxxxxx>: > " From: Ken Ames <ameskg@xxxxxxxxx> > " > " The 70 manual says the H78-14s have 749 revs per mile. > " Nearest 14s are 235/75 (754) or 255/70 (749) and > " for 15s are 235/70 (752 ) and 225/75 (743). > > my 'tire' program - provenance unknown - says > > Specification Sidewall Radius Diameter Circumference Revs/Mile > Difference > 235/75-14 6.9in 13.9in 27.9in 87.6in 723 > 0.0% > 255/70-14 7.0in 14.0in 28.1in 88.1in 719 > 0.6% > 225/75-15 6.6in 14.1in 28.3in 88.9in 713 > 1.5% > 235/70-15 6.5in 14.0in 28.0in 87.8in 722 > 0.3% > > the revs/mile doesn't agree with ken's data but i don't know how it > calculates it. > > many '80s rwd mopars - lebaron, mirada, etc; all volare derivatives > afaik - have 15x7 steel rims that fit amcs perfectly, and would be > just right for 235/70s but of course don't take amc hubcaps but would > take 15" amc wheelcovers. i imagine 15x7 mopar aluminum rims would > fit just as well but haven't tried them. > ________________________________________________________________________ > Andrew Hay the genius nature > internet rambler is to see what all have seen > adh@xxxxxxxxxxxxxxxxx and think what none thought > _______________________________________________ > Amc-list mailing list > Amc-list@xxxxxxxxxxxx > http://www.amc-list.com/mailman/listinfo/amc-list > _______________________________________________ Amc-list mailing list Amc-list@xxxxxxxxxxxx http://www.amc-list.com/mailman/listinfo/amc-list