Type a gear ratio in the left string gadget and leave the right string gadget set at 1. Or you can enter the number of teeth on the ring in the left input and the number of teeth on the pinion in the right input. Engine Speeds will calculate the overall ratio and display it below the inputs.
This gear ratio will be copied to every gear. If you have more than one final drive you can change the final drive in each gear column. See Gear Ratios.