Is the why the detach trailer was born

Can you over spec a truck? Sure... Can you misrepresent the Application? Sure...

The intended service, body/trailer type is important. Example: A salesman, selected crane, but couldn't get the sales tool to allow the suspension he wanted, so changed to flatbed. The factory built as ordered, and the customer refused the trucks. Any chassis, if miss-represented, can lead to component failure and no warranty.

Does a simple 18 end dump (4 pushers) require a 22,800 steer axle and 22/23K spring? Simple and Supers are designed for federal bridge. If specing state/local bridge, usually fewer axles needed.

Federal bridge allows 20K max. The larger springs are required for the Creep/Site when all 4 are raised. Axles are designed to handle the added weight, but the springs, tires, hubs, wheels, steering gears may not.

20K Creep, Dana designed for 28K, Meritor 30K, but check the steering gears. Calculated creep (lift axles raised) on a simple 18, steer is 24,800 lbs. Thus the larger axle is not required, but steering would need 25K min. Any axle with pusher/s require larger gear/s. 20K springs, will work for a while.

Frames can be over designed with taller, inserts/outserts/reinforcements. Engineering is fine with overdesign. They will make adjustments if under. Don't automatically add an insert/outsert. Going to a larger single frame to achieve the RMB's could be preferred.

Drive axles and suspensions. Simple 18 w/federal bridge, calculates about 43,200 lbs. Creep rating on a 40K rated axles is 58-60K. 46K is 60K-65K. 40K suspensions range from no creep to 60K. 46K - 60K to 70K Simple and Super's should not be use off road where weight is determined by how much material is mounded in the box.

If customers adjusts routes where portable scales aren't, then over design might be in order.

Lift axles. 8K (one state doesn't allow), 10K, 13.5K, 17K, 20K, 23K or 25K. The 8/10K axles are light weight and can handle 4,666 ea. loading on a super and 5,750 on a simple, however neither can handle much if any off road. Both are great for stock piling. The 17.5K tires run around 100 MPH with a 75 MPH chassis (315 steer tires), which leads to hub/tire failures (beyond design limits). The 13K is designed for some abuse with 22.5's, but weigh and cost more, thus less payload.

If the customer is failing components, it's best to determine why, before copying what was designed previously, regardless of OEM.