The number of axles on a truck depends on the type of truck and can range from two to five axles, but If there are additional trailers attached to the truck, the number of axles may exceed five. The average four-wheel truck has two axles, while 18-wheel trucks have five.
Eighteen-wheel trucks have two sets of tandem axles with a single axle up front under the trailer. A tandem axle is a set of two axles where one axle is immediately followed by another. This distributes the load weight over two axles, making it easier for the load to be within legal limits.