Hope you won't mind my pitching in late here.
If the cards for Downforce are the same as those for Top Race, can I also play Downforce simply as a straightforward racing game, first across the line wins, without the betting mechanic mid-play? The bidding for cars mechanic at the start would stay the same.
Sure. There's a decent chance someone just won't get good enough cards to have a chance of winning -- especially at higher player counts -- but as long as everyone goes in with eyes open, it should be fine.
It's much more viable at 2 players using the special two-player rules.