PAUL - Tom's correct. Back in the "Good Old Day's" of pulling there were weight classes of 5000#, 7000#, 9000$ and 12,000#. The exact weights varied a bit over time, and some places also had a 15,000# class. Also there were "Stock", "Modified" and "Open" classes, tractors that looked like tractors, tractors with car, airplane, turbine, or industrial engines, and the Open class was "Run what Ya' Brung!"
An evening of pulling started about NOON, weigh-in and registration, and some tractors would run in three or four classes. So they weighed the tractor in for the 5000# class, then threw all the weights on it for each heavier class. Then for the first class the extra weights had to all come off, and then by the end of the night all go back on. A typical pulling team was composed of the driver & tuner and about SIX big strong brutes that could throw 150# wheel weights around easily. Those bars welded onto the wheel & rim were to be able to slide 3-4 IH wheel weights in quickly without messing with hardware. Lot of pulling wheels I've seen those bars were much longer, 8-10 weights were common. That's also the reason IH suitcase weights are worth $1/pound even today because an easier way to add ballast has NEVER been made.
With today's pulling technology, a serious puller builds a tractor for each class so He/She doesn't have to take 7000# of extra iron to every pull.
Those pullers who ran green tractors also did the same thing with their rear wheels, but jd rear weights have a round hole in the center so just a huge pipe over the end of the axle was all they needed. When the green tractors ran out of power and stopped the weights would still be spnning for a short time. Back in those days You would see many IH's, lots of JD,s and a couple Minny's, and J I Case, maybe an Oliver, and a Ford or two.
First few big tractor pulls I ever went to they had men standing along the track every ten feet on both side of the track jumping on the weight sled. To weight the sled up for bigger tractors they'd park tractors on the weight sled. Took a BIG pull-back tractor in those days even when all the men got off the sled! Can Yo imagine what insurance would cost NOW for a pull conducted like that!?!?!?