Which Axle Drives in an Eight-Wheeler?
3 Answers
An eight-wheeler is rear-axle driven. Below are relevant details: Drive Axle: Positioned at the end of the drivetrain, it alters the speed and torque from the transmission and transfers them to the driving wheels. The drive axle typically consists of the main reducer, differential, wheel transmission device, and drive axle housing. A steering drive axle also includes constant velocity universal joints. Additionally, the drive axle bears vertical, longitudinal, and lateral forces between the road surface and the frame or body, as well as braking torque and reaction forces. Differential: An eight-wheeler generally has a mid-axle lock. When the mid-axle lock engages the mid-axle differential, both the mid and rear axles drive together; otherwise, only the rear axle drives.
A tri-axle design is typically used for rear eight-wheel trucks, with three axles distributed under the vehicle. In the conventional layout, the front axle is responsible for steering, while the last two axles serve as the main driving force. Particularly, the third axle, which is the rearmost one, is almost always equipped with driving functionality. Some models feature a liftable second axle, which can be raised when the truck is empty to save fuel. Common drive configurations for these trucks are 6×4 or 6×2. A 6×4 configuration means both the last two axles are driven, providing stronger power, making it especially suitable for hauling heavy loads at construction sites. A 6×2 configuration usually has only the third axle driven, offering better fuel efficiency for high-speed logistics operations. By examining the tire marks on the fenders, it's clear that the axle doing more work shows more noticeable tire wear.
Veteran truck drivers know that the power of an 8-wheeler mainly relies on the rear tandem axles. The third axle is the absolute core drive axle, and you can hear its gears roar every time it climbs a slope. Some trucks have the second axle equipped with drive, but it's more common to see only the last axle as the single drive. On construction sites, many dump trucks have the second axle as a lift axle that doesn't participate in driving—it lowers to share the load when heavily loaded and lifts up to reduce fuel consumption when empty. The drive configuration determines the truck's power: a 6×4 all-wheel drive is best for heavy-duty work, while a 6×2 single drive is more economical for long hauls. When choosing a truck, you need to consider what cargo you're hauling and what roads you'll be traveling on.
