At the conclusion of the pilot's second flight in the accident airplane, he landed the airplane at the destination airport. During the landing rollout, the airplane began to drift to the right. The pilot attempted to correct the drift by applying left rudder but the airplane continued to the right. He then applied what he thought was the maximum left brake and rudder to counteract the drift, but the airplane continued off the right side of the runway, impacted a taxiway sign, and came to rest in a grassy area. The airplane sustained substantial damage to the right wing spar. The pilot later determined that due to his large stature, his foot was likely contacting the firewall instead of the rudder pedal, which inhibited him from applying maximum left brake and rudder. The pilot reported there were no preexisting mechanical anomalies with the airplane.