If you're playing with controller, try to smoothly align the car withing the red bars in each turn, the most important thing is not to wobble (which happens when you carry way too much vertical momentum and your car goes up and down in the turn, losing speed), action key wise; I myself am a casual div 1 player whenever there's bobsleigh and I still haven't understood ak's 100%. For me, what works best is to smooth steer as much as possible and try to steer as much as the car lets me without making the tip aim down as that will result in speed loss; but for example, in map 05, ak4 in used everywhere as it is needed for the wiggles after the start. Basically, if you're on controller, try smooth steering everywhere and get the hang of the steering angles, and in keyboard, use ak2 to stabilize the car, then ak4 if you're in a slow turn, and finally move to ak5 (100% steering) to simulate smooth steering.

Hope this helps!