I was building a truck online and it asks your prefered axle ratio size.
The drive axle is said to have a certain axle ratio, this number(usually a whole number and a decimal fraction) is actually a comparison of the number of gear teeth on the ring gear and the pinion gear, example, a 4.11 means there are 4.11 teeth on the ring gear and one tooth on the pinion gear, or the driveshaft must turn 4.11 times to turn the wheel once, actually on a 4.11 rear there might be 37 teeth on the ring gear and 9 teeth on the pinion gear, by dividing the number of teeth on the pinion gear into the number of teeth on the ring gear the numerical axle ratio 4.11 is obtained, axle ratio also helps increase torque and also determine engine rpm at cruising speed.
Axle ratio is the input/output of the rear end. This is depends on the expected use of the vehicle, engine torque output, transmission gearing, tire sizes to be used, etc. All elements need to be compatible with others to offer best pulling and fuel economy.
