WDH and airbag setup Question

2500HDee wrote:
These discussions seem to be endless in forums across the internet. The weight distributing hitch is to restore the weight to the steer axle and put some of the tongue weight on the trailer axles.

The height of the rear of the tow vehicle does not matter and you can air up before or after you hook up your WDH but make sure you end up with the front at or slightly higher than the measured height before you connected the trailer.

Both the WDH and airbags/stiffer leafs/add-a-leafs/Timbrens/etc will affect the weight on the front axle. The difference is the rear suspension will change this regardless of whether a trailer is attached or not. Ever seen that guy with a whole pallet of shingles in his F-150? The front tires almost come off the ground on every bump. Since he can't use a WDH to transfer the weight to the front axle of his truck full of shingles, the other option, assuming it would not exceed the RAWR or GVWR of his truck, is to have stiffer rear springs. By bringing the back of the truck back up it will restore weight to the front axle and make the truck safe to drive. This can be illustrated with a simple free body diagram. This can be done the same way with a trailer on.

The easiest method is to:
1. Measure front ride height.
2. Connect trailer.
3. Adjust air bags.
4. Measure front ride height.
5. Adjust WDH to achieve front ride height at or slightly above step 1.

If you add too much air in step 3 then you won't be able to add any tension to the spring bars without bringing your front ride height below the initial level and therefore cannot transfer any weight to your trailer axles.

If the front is at or slightly (1/2" to an 1") above the initial value and IF the rear axle, tires, hitch, and payload of the truck can handle this amount of tongue weight, you don't even need a WDH. (This was the case with my last truck without even needing air bags.)

If not, you need to let out some air so that you can actually use the WDH.

This is about distributing the weight to the axles of the truck and trailer and is simple statics. This is not rocket science.

Requirements:
Front axle of truck -> should have the same or slightly less weight (height) than unloaded.

Rear axle of truck -> do not exceed RAWR (height does not matter)

Both axles of truck combined -> do not exceed GVWR

Hitch -> do not exceed weight rating (either with or without WDH, there are separate ratings)

Trailer axles -> do not exceed GVWR

Entire rig -> do not exceed GCVWR

How you arrive at the weights on each axle does not actually matter, only that you use what you have (WDH, airbags, self leveling suspension, unicorn farts) to keep the axle weights within these guidelines.