Calculating the final drive ratio is easy. Understanding the difference between “higher” and “lower” gears is a little more difficult.
The final-drive ratio is so named because it’s the last time gears are used to multiply power as torque is transferred from the engine through the drivetrain to the drive wheels. This ratio is the numerical relationship of the ring and pinion gear found in the rear differential on 2-wheel-drive trucks and both the front and rear differentials on 4-wheel-drive vehicles. The final-drive ratio is calculated by dividing the number of teeth on the ring gear with the number of teeth on the pinion gear. So a ring gear with 43 teeth and a pinion gear with 10 teeth equates to a 4.30:1 ratio.
Tundra offers three final-drive ratios, depending on the engine choice and other equipment: 3.91:1, 4.10:1 and 4.30:1. With the 3.91:1 ratio, that means the driveshaft turns 3.91 times for every complete rotation of the drive wheels. With the 4.30:1 ratio, the driveshaft turns 4.3 times for every rotation of the drive wheel.
To move the truck the same distance—one rotation of the drive wheels—the engine turns over fewer times with the 3.91:1 ratio than the 4.30:1 ratio. A lower numerical ratio tends to offer better fuel economy, especially at highway cruising speeds because the engine doesn’t work as hard. The higher numerical ratio provides greater torque multiplication for more pulling power and quicker acceleration. The engine works harder when trading speed for torque, therefore fuel economy can suffer.
Confusion often surfaces when talking about final-drive ratios with customers, especially enthusiasts. The terms “higher” and “lower” may have different meanings at different times. A customer looking over a Tundra with a 3.91:1 final-drive ratio may ask for a “lower gear” to go off-roading. Toyota doesn’t offer a numerical ratio lower than 3.91:1, but in reality, the customer is asking for the 4.10:1 or 4.30:1. To this customer, lower means a higher numerical ratio because that provides more torque for off-roading.
Another customer might be considering a Tundra with the 4.30:1 final-drive ratio and ask for a “higher” or “taller” gear to help improve fuel economy. Again, Toyota doesn’t offer a numerical ratio higher than 4.30:1, but the customer is really seeking the 4.10:1 or 3.91:1 to reduce the engine speed.
Why do some customers use reverse logic when discussing axle ratios? It most likely relates their interaction with a transmission. The “lower” or “shorter” gears provide more pulling power and torque, even though 1st and 2nd gear have high numerical ratios. The “higher” gears in a transmission reduce engine workload and are used for cruising and fuel economy, even though 4th, 5th and 6th gears have very low numerical ratios. So it’s important to understand the customer’s context when discussing final-drive ratios.
Tundra customers may not always have a choice between final-drive ratios. The 3.91:1 is limited to the 4.0-liter V6 engine and certain packages such as the tow package require specific axle ratios. Tundra, however, gives all customers an outstanding transmission with a wide gear span to provide low-end torque and top-end economy. Toyota has engineered an effective balance between the gear ratios in both the 5- and 6-speed automatic transmissions and the final ratio to surpass most competitors in towing and payload while remaining competitive in fuel economy.