A gear ratio is the quotient of the teeth in the two gearwheels of the gearbox. The 7th gear ratio is generally near to 1 (this could be 62/64, 71/72 or 46/48 for example). The ratio of 1st is the smallest, or the shortest, the ratio of 7th, the longest.
The gearbox ratios must be adjusted and adapted to the style of each circuit.
Use the short gearbox to have a better acceleration, on the tracks that contain many curves and less straight lines, and use the long gearbox for a greater top speed.
Each car has a default set of gearbox ratios. Anyway, the player can adjust and edit his own set of gearbox ratios according with his driving style, or play with the gearbox proposed by default.
To play with the gearbox ratios configured in the edit page, the CUSTOM box must be checked.