accidents. Starting in April 1995 the FAA carried out flight test experiments to determine whether the tundra tires were a contributing factor. The tests used a Piper PA-18-150 Super Cub equipped in sequence with five different sets of tires, including standard factory tires and tundra tires up to diameter. The PA-18 was operated at different weights and center-of-gravity positions. The testing on the ground revealed that the larger the tire, the more restricted the forward visibility on the ground, that there was a nose-down pitching moment when the tires contacted the ground on landing, particularly on a wheel landing, and that tundra tire-equipped aircraft have substantially poorer ground handling characteristics on pavement. In the air, the use of tundra tires reduced top speed, rate of climb, angle of climb, range, useful load and stall warning buffet margins. The tests did not indicate that tundra tires raise stall speed, but did find that, due to increased drag in turns, the aircraft's nose tends to drop excessively with an increase in bank angle. If the pilot counteracts this tendency with rudder and stalls the aircraft, the airplane will rapidly enter a spin. Alaska bush pilots disputed the experimental findings, but, as a result of these experiments the FAA required that all installed tires be subject to a Technical Standard Order or Parts Manufacturer Approval, have been flight-tested and subject to a weight and balance report, determining an acceptable flight envelope. The FAA also limited tundra tires to in diameter, eleven inches (28 cm) short of the largest original Goodyear "airwheel" tire size available in 1930. Operators Until the end of the 20th century tundra tires were mostly used by bush operators flying in remote areas. In the early part of the 21st century many sales of tundra tires have been to recreational pilots. Bill Duncan, president of Alaskan Bushwheels a tundra tire manufacturer explains: Charles McDowell, an Aviat Husky pilot stated: References External links Old Rhinebeck Aerodrome's Great Lakes 2T-1MS biplane and Curtiss-Wright CW-1 Junior monoplane, both fitted with original Musselman/Goodyear "air wheel" precursors to tundra tires.(Archived files from October 20, 2014) Tires Aircraft undercarriage