You really need the gear ratio too. But you can figure the difference between the tire sizes just by stating any rpm and gear ratio, then change only the tire diameter. I use the tire size and gear calculators at www.4lo.com only because it's an easy site to remember. Forget about the "LT" in front of the tire size, and put a "1" in for the transfer case ratio (1:1 = no t-case reduction). Use "1" for the trans ratio (high gear in a three speed, manual or auto). You will also need to find the equivalent P-metric tire size for an E78-14 or the approximate diameter of an E78-14. Should be able to find that in a search. The tire size calc at 4.lo will give you the diameter of the 185/78R15. ------------------ Date: Fri, 22 Jul 2011 10:53:38 -0500 From: Jack Jefferson<pajack1939@xxxxxxxxxxxxx> I have a 1966 Classic with a 232 6 3 speed overdrive. The car came with little E 78 14 tires. I now have 185 78 15 tires installed. My question is what is my actual horizontal rate of velocity at 60 MPH indicated with the 195s installed? -- Frank Swygert Publisher, "American Motors Cars" Magazine (AMC) For all AMC enthusiasts http://www.amc-mag.com (free download available!) _______________________________________________ AMC-list mailing list AMC-list@xxxxxxxxxxxxxxxxx http://list.amc-list.com/listinfo.cgi/amc-list-amc-list.com