>I think you skipped a step in your calculations about tires, and that the
>difference between 205/70 and 205/75 is not as large as 7%.  Am I hasty,
>or were you?  205 * .7 = 143.5 and then double that and add the rim size
>(after converting it from inches), right?

Yes, thanks for pointing this out, Bill. Let me try again:
205/70/14: 205 x .7 x 2 + (14 x 25.4) = 287 + 356 =  643 mm diameter;
205/75/14: 205 x .75 x 2 + (14 x 25.4) = 307.5 + 356 = 663.5 mm diameter.
Hence % difference is only about 3.2%. Did I get it right this time?

Sami