Without a doubt, the least understood mechanical jargon in the realm of 4WD sports is the vehicle’s gear ratio. In a nutshell, the gear ratio is the combination of gears inside the transmission that turns synchronously, making the vehicle move forward or back. Having a combination of gear ratios gives a vehicle the ability to start rolling, climb inclines and cruise along highways. Without gears, a vehicle would only run on a single speed, and that would be the speed the engine is turning.
On real 4WD vehicles, a low-speed transfer case with “low-range” gears gives the engine a mechanical pulling leverage. For every complete revolution of the engine, the low-range gears turns the driveshaft but at a very small fraction. To site an example, an engine may revolve 10 times just to make the drive-shaft make one complete revolution. With this low gear engaged, the speed of the vehicle maybe slow, but the pulling ability will be extremely powerful.
Low-gear ratios are needed to allow 4WDs to crawl over obstacles and loose terrain by utilizing the engine’s pure engine torque, as more power is transferred to the wheels. So basically, a lower transfer case gear ratio is best for off road use.
The next time you go out to shop for a real 4WD, it is best to find out the ratio of the transfer case. A typical transfer case ratio would appear as 1:2.6: the first number (1), stands for the number of times the engine revolves, while the second number (2.6) stands for how many times the low-gear revolves. The best low-range gear ratio I know from a vehicle straight out of the factory is a 1:4.1.
But the gearing game does not end there. After the engine speed is converted by the transmission and translated by the transfer-case to speed and torque, there is another set of gears that will finally dictate how slow or how fast the vehicle will go. This is called the final-drive ratio gear that can be found on both the front and rear axles. A higher numerical gear ratio on the final drive will translate to a “lower speed” on the final drive, which means you will be having better acceleration and improved fuel economy around the city but higher engine speeds from highway driving conditions. A numerically lower ratio will mean smoother acceleration but not really fast. It will also give better highway top-end speeds with lower engine revolutions. For off-road use, a higher number is best.
Complicated? There is more. Usually with new off-road enthusiasts, as soon as they can fit the largest set of tires possible on their vehicle, they are surprised to find out that their vehicle no longer accelerates as well as it used to, as compared to the standard-sized tires. This is because they have altered the final gear ratio of the vehicle because of the larger diameter of the new tires In a nutshell, it means the vehicle is now “walking on longer legs and will require more mechanical effort to get it to start roiling.” Larger tires are also heavier. When that happens, off-roaders then begin to hear the word “re-gearing.” This jargon means that a new combination of gears must be installed to compensate for the heavier load and provide the engine more pulling power.
It takes a lot of trial and error to find the right gear combination for both the transfer case and the final gear as it all depends on the driving style and the intended purpose of each vehicle and its owner. Whether it will be utilized as a multi-use, day-to-day vehicle on the weekdays, and then an extreme off-roader during weekends, the right gear combination really depends on the user. Finally, when you think that you’ve finally found the correct gear combination, it does not end there. Do keep in mind that with all the additional torque multiplication from the transfer case and final drive, plus the additional weight of an upgraded tire, it may now be too much for your stock axle shaft. To compensate for all the additional power and weight, a much stronger shaft must be installed to prevent the axle shafts from snapping in the most inconvenient of time, usually while in the trails.