Choose any stage - preferably one in Finland with fast sections and plenty of trees next to the road. Keep hitting the trees at high speeds. The objective is to destroy the engine (it has to turn fully red), because that's when the car will be unable to continue aka it will be totaled. The car will be driving much slower after the engine has been severely damaged so always make sure to gain some speed before hitting the next tree (or any other indestructible obstacle).