acdii

Hmm, good point.

Flamingtaco

Do those things change the suspension geometry? If not, then not technically, but I'd bet you'd find resistance to warranty suspension components if Ford finds out any of those were on an axle. Products sold by Ford, on the other hand...

kbroderick

Yes, it does. The whole truck is engineered and tested as a system to reach those ratings. As soon as you change any material component of that system, you're now operating a truck that has not had the same engineering applied, nor passed the same testing.

Applying a bit of common sense, it's highly unlikely that some form of load-assistance system would decrease the actual ability of the truck to handle the forces it was originally engineered to handle (and may mitigate some issues involved in operating near, at, or perhaps even over those factory limits), but the original Ford engineering and testing work is no longer 100% applicable, and they'll wash their hands of the results.

It's also possible that by strengthening one part of the system, you end up applying more (or different) force to another. Without having access to the original engineering work, it can be tough to verify that upgrading one part of a system isn't going to encourage failure somewhere else. The reductio ad absurdum example would be that if you upgrade a fuse but not the wiring it protects, you're potentially introducing more electrical load on that wiring and creating a fire risk.

Yes, there's a counterargument that you will need to change elements of the system due to wear and tear during its useful life (e.g. shocks, tires, brake friction surfaces), and particularly with respect to tires, you should be able to substitute another tire with the same size, load rating, and speed rating without materially impacting the overall system rating. But a major suspension change—even if it improves the overall handling of the truck, or the handling of the truck for your use case—is still a major change that pushes the entire system outside of the design & testing envelope.