Well, it does help to know about some details of speed. The steps of 4 is one thing. The cap of 252 from the sum of motor, nitro, and zipper is another thing. As for the two hidden nitros, the CPU actually does pick one of them up, so if you're not first there, you miss it. I haven't stumbled over other hidden goodies myself, so I'm wondering if these hidden pick-ups are a mistake.
Alright! Criticism! Now to either explain myself or confirm the problem!
Wide turn in race 5: The first lap, I had a nitro to pick up. This means avoiding a second zipper right before the jump. On the second lap, my excuse is that I hit the second zipper. So, I just hug the outer wall for "free" steering despite being in mid-air at the time. Mind, being at the outer wall is, rest assured, not taking that corner tightly, so it's certainly worth a few tests to see if slowing down the jump is worth it.
Missed zippers for nitros:
Race 10, the zipper I miss for a nitro is very close to another zipper I do hit, and is itself not exactly an ideal position to drive to. It's a small number of frames loss, likely less than 15 based on some quick calculations (I have zipper speed for 18 frames before that second zipper), but one to consider anyway.
Race 14, I spend every nitro I had. Skipping a nitro means not getting its 30-ish frames of savings, and those zippers are pretty close together. There are four nitros, grouped in two pairs, that I pick up, and not picking one up probably means not picking the other. By my count, two ideal nitros beat one ideal zipper, and these zippers are among the least ideal due to being grouped so close together. That said, it may be worth checking if the CPU avoids the first pair of nitros for me to take on the second lap, as I don't need to spend them all that rapidly. This is simply not a race where I can skimp on picking up nitros, as I end with 0, and it's rather difficult to end with -1.
Race 15, that money bag on that corner just before going under the bridge? Considering how tight I can take that corner, I see a pretty significant amount of distance between the corner and the bag. Okay, granted, Blue Car would have more time to push me if I take a wide turn to grab it, but that's a painful turn. ... Wait, you mean the bag that Blue Car takes in the short straight segment before going over the bridge? Ah, that one is not so bad, probably only several frames out and back. Might be worth a look.
Wide turn in race 21: I don't like jumps. I keep wondering if I should slow down before the jump, trashing my speed for the entirety of the jump so I can turn earlier. In this particular case, the answer looks likely that I should trash the jump speed for a better cornering, as I do take it pretty wide. You can view a more extreme version of the speedy jump by looking at the CPU cars crashing into the far wall at that same spot.
Change in corners handling: I'm more careful about how I crash into them. If I don't touch them, I don't lose speed. The instant I'm two units below maximum, tight steering will continue to decrease my speed, and hitting a corner is enough to trigger this chain reaction of a loss. One particular type of corner doesn't eat into my speed, and actually helps to speed up shift in momentum, but it's difficult to track the exact micro-positioning changes of touching the corner, and driving too hard into that corner will slow you down anyway because you have a bad angle, whether or not it affects your speed. In any case, I'm still trying to adjust my timing of when I make my tight turns so that, one frame earlier, I hit the wall. Actually, I also adjust positioning at times, so that one frame difference of this light positioning, I hit the wall. Once in a while, I do still intentionally hit a wall, like in race 14 after the six zippers hall, as I need the cornering much more than the speed.
Also, probably the big thing is that most of my strategizing on these tracks are actually single-pass. Which is to say, I take whatever looks fast at the time, then drop things there and don't test other routes that might turn out faster. Basically, pioneer out something, get it under scrutiny of however many who want to look at it, then I can go back and patch any problems that, while I may catch a bunch of them myself, certainly wouldn't hurt to get someone else to help catch them as well.