Hello, and welcome to my guide on optimizing your nitro use. This guide will be separated into two parts: early game nitro optimization and late game nitro optimization. Some of this guide is theory based on math, and some of it involves some newfound tech. Hey-o!
===================== Early Game Nitro (100% Runs)
At this stage in the game, you'll be going worlds slower than during the late game. When starting a track, I don't usually boost to begin with (the idea here is that the boost will get you to your top speed more efficiently than if you didn't boost). However, because the different in speed between your max normal speed and max nitro speed is not too vast (it's not more than 20-30 MPH during the start of the game), I try not to do so. Moreover, you could get a speed boost in the form of a bump from a CPU. Instead, I try to pool nitro usage to be closer together.
I'll give an example. In Auckland (the first track), your max speed without nitro will be around 130 MPH, and around 160 MPH with nitro. With these numbers, let's instead imagine we're on an flat terrain that stretches infinitely. If we define a boost to last exactly 10 seconds (from 0.0 to 10.0, and we define acceleration and deceleration to be 5 MPH/sec, we find that someone that uses his or her second boost at a point where the speed is between both the max normal speed and max nitro speed gets more efficiency out of a nitro than someone that waited until after they decelerated to their max normal speed. This person is also more efficient than someone who uses a nitro immediately after their first one ended.
Still don't understand? Check out this spreadsheet (link on the word "spreadsheet", including this word) I made exactly for this purpose. It's a bit more clear than just words. I've made the spreadsheet so that the period of time stretches over a minute, and that someone uses three boosts over that very minute. Again, this is a theoretical, but very implementable in practice and runs. :D
Late Game Nitro (Both Any%/100%)
By late game, I'm assuming that you have the best engine, the best gearbox, and some form of a nitro upgrade. At this point, the range between your max normal speed and max nitro speed should be a lot larger. Keep using nitro in the manner above. However, there's something that I've noticed that occurs at certain speeds that I'm going to call...
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- Extended Speed Tech -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
Once you have the best engine, the best gearbox, and some form of a nitro upgrade (second-best or best, especially), you'll also obtain a benefit where your deceleration slows at a certain speed. This point where your deceleration slows down almost dramatically is around 228-235 MPH, or around 276-286 KM/H. Once you decelerate below the lower cap for these numbers, you'll see that your deceleration quickens once again. You can use this to your advantage by having your nitro expire as you're on a high point on the map, allowing you to keep at these speed ranges as you're going downhill and abuse the slow deceleration that exists as you go at these speeds.
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Keep the Extended Speed tech in mind during your late game, as well as the nitro optimization that you've been implementing during your early game, and you'll definitely find an improvement in your runs. :D
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Thanks for giving this guide a read, and happy speedrunning!