Liftable and self steering auxiliary axles could help add payload capacity, but they do come with increased weight and additional complexity. A huge amount of engineering is required to get the correct number of axles in the right place on the frame for particular applications in particular jurisdictions. There is a lot more to consider beyond the number of axles you could squeeze into the available frame space.


There is not one single lift axle configuration that works everywhere because of the large variety of state and local regulations applicable to axle weights and spreads. Trucks that are spec’d for use in Ohio, for instance, might not be allowed in Indiana. Local dealers and upfitters will be aware of the types of configurations are allowable, but if you plan to cross different state lines, you might need to settle for a lower common denominator.


Fleets most likely want to maximize their payloads and it is up to the manufacturer to know how to fit steerable and liftable axles under the truck or trailer. 


And while it might seem like a no brainer, you should ensure that the axle will physically fit into the allotted space can be challenging. You need to consider factors such as driveline clearance when the suspension is inflated and deflated, and make sure there is adequate clearance for the tires while turning with steerable axles.


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Understand the ratings

You will usually hear two different ratings that are mentioned when spec’ing lift axles. These are the axle and suspension ratings. It is not uncommon to find, for instance, a twenty-six thousand pound axle with a thirty thousand pound suspension. The rating for the package of axle and suspension will be that of the lowest rated component - so the axle in this case. Spec’ing a suspension with a larger rating than the axle could be done for strength and robustness, not only the load bearing capacity.


Most of the discussion that involve lift axles centers on carrying capacity, but you also need to think about the weight bearing capacity of the truck when the lift axles are raised. With these axles raised, the drive axles and the steer axle are now left to support the full weight of the load. The term many people in the industry use is jobsite rating.


The last consideration is where to put the lift-axle control. Regulations are different around the country, with some that insist the controls be outside the cab beyond the truck driver’s reach, while others let the controls in the cab.


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Courtesy of Cuselleration