"Low ratio" is like granny "LOW". High ratio is like high gear.
7:1 is a low ratio, and 0.7:1 is a high ratio. Meaning the out put from the transmitting device is either high speed or low speed as compaired to the speed put into it. The torque is inverse to the speed. With no frictional losses and other mechanical losses the Horse power remains the same through the system.
So 3.9:1 is lower gears than 3.55:1. In direct gear in the transmission which is 1:1, with a 3.9:1 the engine turns 3.9 times to make the rear tires turn 1 time.
