Only reason I can see that filling the front tires would bad is that you would trying to lift the weighted tires by the king pin assembly when you have weight on the 3PH Vs having the weight hanging on the frame. Not sure if the king pin assembly is designed to hold / lift that extra weight.
I've often heard members say (along with the manuals) not to fill front tires. I've always wondered WHY that is actually not a good idea, and with your post I think it finally makes sense to me. Here's what I'm understanding from you:
Even if not actually lifting the front right off the ground, using implements on the back is still creating "lift" on the front, with the rear axle acting as the fulcrum. The weight of all the tractor parts forward of the rear axle fulcrum, plus any extra weights, etc., keep the front of the tractor down on the ground. As you add weight forward of the fulcrum, you increase the capacity of what you can lift at the rear. Any weight you add that is on the frame is ok, as the frame can take it.
Adding a bunch of weight in the front tires would help in holding the tractor down, but there is now a fair amount of added stress to the parts that hold the wheels, axles, etc., to the tractor. Not downward stress, but upward stress.
Like if you jacked the front end up letting the front tires dangle in the air, the attaching parts only hold up the weight of the
air filled tires, hubs, axles, etc. If you filled the front tires with liquid, those same parts have to hold up MUCH more weight. Doing a lot of work with heavy rear implements and filled front tires is putting a lot of constant additional "backwards" stress on the front attaching parts, which are designed more to withstand down pressure (weight of front of tractor, filled loaders, etc.), but not so much for up pressure.
Am I understanding correctly?
