~Some tips (if you don't understand the video):

How do I get the sg?

1- Down on a downhill and don't jump while you're falling down.

2 - Jump on the edge of the road. It is not simple as the first one, but you can do it with some practice.

3 - Do a double jump on a turbo pad.

A nice tip: If you get a great SG on the road, and you wanna continue froggying by the track, try to touch the first turbo pad of the track, it will give for you a little more of speed (even if you have the sacred fire).