When preparing to purchase a ready mix truck, it is important to consider weight restrictions imposed by state or federal authorities. The federal Bridge Law controls the spacing of axles on trucks to help reduce pavement damage. The equations sets limits on the amount of weight distributed over a given number of axles. Therefore, the more axles on a truck, the more weight it can carry. There are two types of additional retractable axles that can be added onto a truck--pusher axles and tag axles. Pusher axles are located in front of the drive axle, and tag axles are located behind the drive axle. Both are non-powered. Pusher axles increase the number of axles but do not increase the wheelbase, whereas tag axles increase both the number of axles and the wheelbase. Another way to increase allowable load is to specify aluminum components where available. These components can include battery boxes, bumpers, cabs, exhaust systems, air and fuel tanks, and wheels. In addition, lightweight engines and transmissions may be available. Be careful specifying lightweight materials on heavy-duty vehicles. By saving weight, you may lose durability.