I'm assuming 27" stock tire diameter. I'm not using any formula, I am just using ratio's.

27/3.07 = 33/X solve it and you get 3.752222......

If you assume 28's

28/3.07 = 33/x you get about 3.62

This also works for tire size and gear ratio.

28/3.07 = X/3.73 x = 34.01ö 27Æs stock would be 32.8ö

I'm sure that's what rock jock is doing.

Sorry BJ, I just read your post to fast... and wrong. I though you meant bigger tires are harder to turn from size and weight difference not load and RPM differences....

The whole post is regarding the latter.

Carburetors loved going lean during the initial transition to the power system, then richened out once they were fully on it (hence the worse gas mileage). EFI is a lot more linear (not relying on a mechanical system for AFR) so that the transition stays fairly close to center adding a bit of gas mileage.