The rear most axle on a wrecker will be carrying a higher percentage of the load. This is evidenced by the fact that the tires on the rear-most axle wear faster than those ahead of them.
The rear drive axle commonly carries a minimum of 15% more of the weight than the other two in a tandem OR tri-axle configuration. This is because of the way a wrecker carries weight behind the axles as opposed to a semi-tractor coupled to a trailer. In the case of the semi, the trailer’s weight is bearing down directly and most times evenly across the drive axles.
Understanding the mechanics of how a wrecker’s suspension is loaded should reinforce the fact that regular brake inspections, tire rotation and preventative maintenance of the vehicle is required, especially for the rear axles and all of their components. The informed operator should always be aware that regardless of the class and size wrecker you operate, when towing with a wheel lift or under lift, the truck’s rear suspension will almost ALWAYS be overloaded (with respect to its axle weight ratings) before more than 50% of its steering axle weight has been transferred to the rear.