For every one revolutiuon of the tire, the driveshaft has to spin 3.42 times..Its that simple

The higher the ratio the better for towing and accelaration but bad for MPG

"numerically" higher ratios give you a lower gear. for example...

-3.42 = best gas mileage, decent towing, okay off the line power

-3.73 = good gas mileage, better towing capability, good off the line

-4.10 = lower gas mileage, best towing capability, best off the line

depending on what you are looking for in your ride should determine what axle ratio you get. another example...

i have a '68 Tempest. i have a high gear, or "numerically" lower ratio. this number sucks for off the line power. but with the gas it burns, and the cost of gas these days i am not mad. the higher stall converter helps out some. but, i am not into 1/4 mile racing so this is not an issue to me. that's why i said ealier it depends on what you are going to use your rig for. you build it for the way you are going to use it. i am a cruiser. not a street bruiser.

although i would like to go at least 3.73 on the Tempest.

we'll see. i forgot to mention that the "numerically" higher gear ratios give out to the "numerically" lower ones down the road; the engine winds out quicker with the "numerically" higher one; the other guy is still moving out with the "numerically" lower ratio.