On June 16, 1998, at 0900 Alaska daylight time, a tundra tire equipped Piper PA-18 airplane, N4320Z, sustained substantial damage when it nosed over during landing on tundra, about 17 miles north of Talkeetna, Alaska. The solo commercial pilot was not injured. The flight was conducted under 14 CFR Part 91, as a local flight from Talkeetna to practice landings with the newly installed tires. The flight departed at 0730. Visual meteorological conditions prevailed at the time of the accident, and a VFR flight plan was filed. The pilot told the NTSB Investigator-In-Charge during a telephone interview on June 16, that he was practicing landings on tundra, and the winds were generally calm. He stated that during a landing to the south, he encountered a slight tailwind gust. The pilot hit the brakes, and the airplane nosed over onto its back. He wrote in his Pilot/Operator Report that he made an error in determining wind direction and speed.