What Does the Rear Axle Ratio of a Truck Mean?

[Jacob]

Truck rear axle ratio refers to the gear transmission ratio of the main reducer in the truck's drive axle, which is equal to the ratio of the rotational angular velocity of the driveshaft to the rotational angular velocity of the axle half-shaft. Below is relevant information about the rear axle ratio: 1. Key Factors: The rear axle ratio is related to the gears. The power output from the engine and transmission acts on the driveshaft, which rotates to transmit power to the pinion gear of the main reducer, driving the ring gear of the main reducer to rotate and subsequently turning the half-shaft. 2. Calculation Formula: Number of teeth on the ring gear of the main reducer ÷ Number of teeth on the pinion gear of the main reducer. In simple terms, when the driveshaft rotates N times to make the half-shaft rotate once, this N is the rear axle ratio.

[SanDakota]

The rear axle ratio of a truck is essentially the proportional relationship between the driveshaft speed and the rear wheel speed. Simply put, the engine's power doesn't go directly to the wheels—it first passes through the transmission and the gears in the rear axle for torque multiplication and speed reduction. A higher rear axle ratio means the wheels turn slower at the same engine speed, providing more pulling power, which is especially useful for hauling heavy loads or climbing steep slopes. However, this comes at the cost of higher fuel consumption at highway speeds. Conversely, a lower ratio improves fuel efficiency on highways but struggles with uphill climbs. This number is usually stamped on the rear axle housing, with common ratios like 4.11 or 3.73. When choosing a truck, consider whether you'll mostly drive on mountainous terrain or highways, and ensure it matches well with the transmission gear setup. Last time I drove a truck with a 4.875 ratio hauling timber up a steep slope, a neighboring truck with a 3.4 ratio was spewing black smoke even at full throttle.

[McDallas]

I call the rear axle ratio the 'leg power' of a truck. Think about it, there's a set of gears in the rear axle where the engine turns several times for the tire to turn just once—this ratio is the axle ratio. A higher number means the wheels 'walk' slower but with more strength, like a person carrying heavy loads taking small, steady steps; a lower number means faster steps but less strength, suitable for running empty on fast roads. I've seen people blindly increase the axle ratio to boost pulling power during repairs, only to end up with the engine screaming at terrifyingly high RPMs on the highway, costing more in fuel than the toll fees they saved. In reality, the factory design is well-considered—the axle ratio must match the transmission and engine power. Before making changes, it's crucial to calculate the optimal RPM range for fuel efficiency.

[Kevin]

The rear axle ratio determines how fast the wheels rotate. The ratio number is the value of engine speed divided by wheel speed. For example, a ratio of 6.5 means the engine turns 6.5 times for every 1 rotation of the tire. Trucks hauling ore typically use a ratio in the 7s, and reaching 80 km/h when empty is already considered good; delivery trucks often use a ratio in the 3s, allowing them to reach 110 km/h while also being fuel-efficient. This parameter directly affects climbing ability and top speed, so it's important to check carefully when selecting a vehicle. Last time, a driver complained about his new truck lacking power—it turned out the fleet had mistakenly assigned him a truck with a 3.5 ratio for hauling gravel, making it useless even with the accelerator floored when climbing hills.

[CarterLee]

The gear ratio can be understood as the gear shift on a bicycle. A high gear ratio is like the lowest gear, requiring more effort to pedal but capable of climbing steep slopes; a low gear ratio is like the highest gear, making it easier to pedal but less effective when climbing. In a truck's rear axle, the tooth count ratio between the pinion gear (drive gear) and the ring gear (driven gear) determines this characteristic. Changing the gear ratio requires replacing the entire set of gears, which can cost several thousand yuan for some single-reduction axles, and even more for wheel-reduction axles. Choosing the wrong gear ratio is like trying to climb a mountain in roller skates—the wheels spin but the truck doesn't move forward.