On September 15, 2000, about 1430 Alaska daylight time, a tundra tire equipped Piper PA-18 airplane, N6760B, sustained substantial damage during landing on a gravel bar, about 20 miles west of Big Lake, Alaska, at latitude 61 degrees, 35.412 minutes north, and longitude 150 degrees, 23.999 minutes west. The airplane was being operated as a visual flight rules (VFR) cross-country personal flight when the accident occurred. The airplane was operated by the pilot. The private certificated pilot, the sole occupant, was not injured. Visual meteorological conditions prevailed. The flight originated at Merrill Field, Anchorage, Alaska, at 1400. During a telephone conversation with the National Transportation Safety Board (NTSB) investigator-in-charge (IIC), on September 17, 2000, the pilot reported that his airplane is equipped with 30-inch tundra tires. He recently installed extended landing gear to add distance between the bottom arc of the propeller and the ground. He also added new brake cylinders equipped with a "booster" cylinder. During the landing roll, the pilot said he applied the brakes too hard, and the airplane nosed over. The airplane received damage to the rudder, and the right wing lift strut.