The Tsukuba Wet Race is a Special Condition event in Gran Turismo 4. It is a wet tarmac duel race running through the compact Tsukuba Circuit on rainy conditions.
It is possible to use B-Spec in these races by pitting in, being the only Special Conditions event to allow that as the track has a pit lane. This cannot be done in the Japanese or Chinese version of the game, however, as the feature to switch modes in the pits is absent.