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Back in the day, it was nice to put dual fuel tanks under with dual stacks... Symmetry could commonly be achieved with batteries inside the cab, between the rails, or moved to the headache rack.
Today symmetry of fuel tanks is difficult to accomplish. Dealing with the DPF/SCR/DEF components of the aftertreatment is a real challenge. Batteries LH under cab with DPF/SCR in the RH position provides a fairly balanced under cab.
Symmetry today is often forfeited to practicality.
Heavy Haul trailers are amazing pieces of equipment.
Some states (3 that I know of) require the ground load on the pusher to be within 10% of the drives when permitted. There is a valve/system that automatically adjusts the lift axle air pressure to satisfy this requirement utilizing an air ride suspension. It is available in the aftermarket, if your OEM does not install in the factory. Reach out if you'd like to know more.
Asking correct questions is paramount. Vocational chassis are tied to local, state, federal bridge and/or permit requirements. The largest payload, is understanding what's allowed.
Vehicle weight ratings are not the same as the local/state or federal highways. Sales folks are absolutely key to designing the correct chassis so finding that person is imperative. Proper specing plus the OEM that can build the correct combination is key. Not all OEM's offer the same options and utilize the same design criteria.
Some requirements can be different than DOT enforcement. Example, tire patch. Axle weight can be tied to tire width, but DOT may use the stamped rating. Example 315/80R22.5, 10K steer tire, however the state has a 600 lb/in requirement, so 315 divided by 25.4" = 12.4" wide X 600 =7,440 lbs. 14,880 vs. 20,000 is significant.
You may have to spec a 425/80R22.5 that is 16.7" wide X 600 = 10,020. Federal Bridge allows 20K/axle, so this tire would be required along with a 12.25" wide wheel with the appropriate offset and axle width for the best turning radius.
If the federal, state, local bridge formulas are not taken into account, the chassis might not offer the best payload. 1" different wheel base can make a 500/1,000 or up to a 8,000 lb. difference. Vocational chassis moving between these areas make proper specing a challenge. Collaboration with the customer for the correct weight is paramount. Reach out if we can help you.
