Final Drive Ratio Calculator
Calculate the overall drivetrain ratio by combining the transmission gear ratio with the rear axle (differential) ratio.
How to use this tool
- Look up your selected transmission gear ratio (e.g. 3.50:1 for 1st gear).
- Find the axle ratio from the vehicle specs or differential tag.
- Multiply them together to get the overall drivetrain ratio.
Find the total mechanical advantage between the engine and the driven wheels.
Formula
Overall Drive Ratio = Transmission Gear Ratio × Axle (Differential) Ratio
How it works
This calculator multiplies the selected transmission gear ratio by the rear axle (differential) ratio to give the total mechanical reduction between the engine crankshaft and the drive wheels. A higher overall ratio produces stronger acceleration but lower top speed; a lower ratio favors highway efficiency. The calculation assumes a single-stage final drive with no transfer case ratio in the path.
Worked example
Worked example
- Transmission ratio in first gear: 3.5:1.
- Rear axle ratio: 3.73:1.
- Overall ratio = 3.5 × 3.73 = 13.055.
Overall drive ratio = 13.055 : 1
Key terms
- Transmission gear ratio
- The ratio between the input and output shaft speeds inside the gearbox for a given selected gear.
- Axle ratio
- Also called the differential ratio; the number of driveshaft rotations required per single rotation of the rear axle.
- Overall drive ratio
- The combined mechanical reduction from engine to wheels, found by multiplying the transmission and axle ratios.
- Final drive
- The last set of gears in the drivetrain — typically the ring-and-pinion inside the differential — that transfers power to the axle shafts.
Frequently asked questions
- What is the final drive ratio?
- The final drive ratio is the product of the transmission gear ratio and the axle ratio. It represents how many times the engine turns for each turn of the wheels.
- How does axle ratio affect towing?
- A numerically higher axle ratio (e.g. 4.10 vs 3.08) increases pulling torque, making it better for towing, but reduces highway fuel economy.