I found a site for calculating differences in tire size. I thought it might be helpful to anyone who's interested in changing to bigger rims/tires:

 

http://www.1010tires.com/TireSizeCalculator.asp

 

BTW, is there any way to change the speedo gearing on the 5sp d/r tranny?

There is no way, but with the diameter difference you can then calculate the % off that your spedo is, and then use a sharpie or whiteout and mark where the 25, 55 and 70 is, or would be if the speedo was accurate, saved me a couple of times.

www.tirerack.com will actually give you the revolutions per mile on each brand of tire.

 

 

 

nipper