TOM H. - Actually, there's a couple guys pulling in the NTPA now that do use wheel weights on the rear wheels of their pulling tractors. It's part of their "Movable weight". It's not like 20-30 yrs ago where they have a dozen 150# weights added to each rear wheel to weight up to heavier classes, there's maybe one small 80# weight per rear wheel.
But Don's talking about fluid, totally different animal than cast wheel weights. Cast wheel weights TURN with the tire/wheel, Fluid does NOT. A fluid filled tire may pull slightly harder than a same size tire/wheel with cast iron weights added to equal the same weight as the fluid filled tire but the force required to turn the wheel/tire with fluid is so minutely greater than the force required to turn the wheel/tire with cast weights added I have NO IDEA how you could measure it accurately.
Best Idea I have is maybe roll one of the fluid filled tires down a long gradual hill and see how far it goes, then roll a wheel/tire with cast weights added to equal the same weight down the same hill and see which goes farther & faster.
Having done ALL Kinds of road work with tractors in hills pulling heavy loads, I really never noticed any difference in hill climbing ability with or without fluid as far as maintaining speed on hard surfaces. A tractor without weight, compared to a tractor with cast iron weight, verses liquid ballast weight. Now get that tractor off onto soft dirt, add in a little moisture in the dirt, AKA MUD, and the tractor without weight will spin out if the load is heavy enough and hill steep enough, the tractor with cast weights added will climb much better, and I'd say the tractor with fluid weight would climb even better still.
You'd have to keep the weights similar between the cast weights and fluid weights. Take my Super H for example, it had 500# of fluid per rear tire, 1000# total. Years ago I also ran one 150# wheel weight per rear wheel and then added a second weight per wheel when I started pushing snow with it. So 600# of iron vs 1000# of fluid. To get back the 1000# of fluid I removed two yrs ago would require SIX more wheel weights, plus a 100# suitcase weight hung on the drawbar. I've seen a lot of H's with one and two weights per rear wheel, but NEVER one with FIVE per rear wheel.