Allen Engineering makes no small claims for its HD550 Riding Trowel. The company says it is the largest, most powerful, most productive riding trowel in the world. Weighing 2,500 pounds, it is powered by an 87-hp Kubota diesel engine that drives its new Hydra-Drive (HD) system. Hydra-Drive is an all-hydraulic drive and steering arrangement that eliminates manual levers, clutches and mechanical gearboxes, making the big machine easy to handle. The HD550 features 60-inch-diameter rotors that are driven by two radial-piston hydraulic motors. Estimated list price: $38,950.