What is a lift axle (on semi trucks) and what is its purpose?

Regardless of whether that “lift axle”, ie an axle that can be lifted so its wheels no longer touch the ground, is on the tractor or on the trailer, it is used to increase the vehicle’s legal weight capacity. read more

So a lift axle does what it says. You can lift the axle which will lift the tire off the ground so that you don’t use the tire when you don’t need the extra axle which will save on tire wear. You can use a standard size wheel and tire, like the duals in this picture, and still get the lift axle to lift the tire off the ground. read more

A lift axle, or tag axle, as it is often called, is a heavy truck axle that is designed to be lifted off the road's surface when not needed. A lift axle can be mounted on the truck, the trailer or both and is commonly found on tanker-style trucks as well as trucks used to haul over-sized loads. read more