He hasn"t weighted it past putting fluid in the tires then. We had one pushing well over 200 hp (think it had a 466 crank in it), when we had it dyno"d the JD mechanic cut the dyno out when it was climbing quickly past 170 at a high idle. When we put weights up front for plowing one year we spun an axle in a wheel center. After that we let her spin a little.
The 15"s had a completely different geartrain, with helical gears and planetary finals. I don"t know what it would take to tear one apart, but ours was turned up to the point you could follow its track around the field by the smoke cloud on a still night pulling the chopper. Its smoke was still moving at a very good pace passing the high tension power lines.