On September 14, 1995, about 1800 Alaska daylight time, a tundra tire equipped Cessna 180 airplane, N2940K, operated by the owner/pilot, sustained substantial damage during landing at an off airport site located approximately 85 miles west of Port Alsworth, Alaska. The solo airline transport certificated pilot was not injured. The personal flight operated in visual meteorological conditions without a flight plan. The pilot reported he was performing a wheel landing on an unimproved site. Shortly after touchdown, the pilot applied braking action and the tailwheel began to settle. He said the left side brakes were very "soft" and he applied opposite rudder to maintain directional control. The pilot feels that the left wheel assembly was coming apart at this point. The left main landing gear stub subsequently dug into the landing surface, and the airplane went up on its nose and left wingtip. Postaccident inspection by the pilot disclosed that the airplane's left wheel, which was modified for tundra tire use with Gar Aero adapters, had split vertically, and allowed the wheel halves to separate away from the landing gear leg. Damage to the airplane consisted of, among other items, a bent left wing spar, a damaged left aileron and wing ribs.