Sent in by David at The Unofficial World of Nintendo!!!
Start a Single Race with either M. Schumacher or E. Irvine. Make sure
that you have selected manual transmission. On starting the race,
change gears until you have reached 7th Gear. Then quit the race,
and enter Grand Prix mode. Start a new season or carry on with
another one. Whichever car you choose it should have 7 Gears.