Farm tires don't weigh all that much, relatively speaking. Couple hundred pounds (for the record, strongman events wouldn't consider 200lbs much in the way of weight. Except for the one time they did a run event using that as the backpack weight) and most of the time you're not shouldering the majority of the weight. Hell, even I can flip or drag 300+lb tires fairly easily and I'm considered a weak fuck by the local hardcore gym.