In case anyone's still around here, I've been interested in speedrunning on Sgt. Byrd's speedways. I've searched if there's any other post or archive on the internet about this topic, but all I found were full game speedruns and not speedway ones. So, here are the best two strats I've developed for Island and Cloudy speedways, both on easy mode (for the dragon egg). I'll be looking into perfecting those strats and making some for the other speedways and difficulty settings as well. I got 1:15 with the Cloudy strat, but it can get much better than that.

Here's a video of me TASing the Island one. The strat is perfectly possible without TAS: https://www.youtube.com/watch?v=EfROEalg3zc