Just a friendly reminder, momentum is extremely important for high level runs!

My level, 'Faster Than Impossible' is all about this. In this level, it contains 18 corners in a downward staircase and 11 in an upward staircase. If you do not optimize momentum, and simply hold the direction you need to go in (and bump your head or wheels on each corner), you will be just over 3 seconds off! Which means every single corner that you bump will cost you about 0.1 seconds! It isn't actually equal for upwards and downwards momentum, though. If you mess up on a downwards corner, it will impact the run significantly more than in an upwards corner, I would estimate closer to 0.15 seconds apiece. This is because when you jump, you get an instant, pretty large, boost upwards, so you will be hitting the corner for much less time, whereas if you are falling, gravity takes time to accelerate you, so you will be hitting the corner much more time!

If you look at, say, Novice Level, there are 8 downward corners that you need to optimize for a perfect run. If you don't optimize them at all, expect to add at least a second to your time. If we look at other, longer levels, especially those where you can't use time saves the entire run or those without rockets for most of the run, you could expect this to be significantly more.