On Sky Garden there is a ramp next to a boost ramp. You can charge up a mini turbo when you are about to go off road and wen you are off road it will go orange. Release R to activate the mini turbo and do a jump on the ramp to get to the other part of the road. On Yoshi Circuit there is a ramp that is covered in grass around the start of the stage. You have to do the same thing you did on sky garden and don't forget to jump when you release R.