How do you guys practice quick turns? is there a good spot to do so and also a video explaining on how to do so?

so i'm a starting runner for this, and one big problem i have is keeping 120fps, i know i should be able to maintain this as i have a GTX 1080 and an I7 but for some reason i hop from 90-120fps even with everything on low, is it just the game or should i see if it's something with my computer?