Q: Ken Roczen used a stiffer suspension at A1 when the race called for a softer suspension. Now I'm confused. Can you tell me the ideal dirt bike suspension setup?
A: The short answer boils down to you. What do you like best and what helps your riding. Ken Roczen went stiff at A1 so the bike wouldn't compress in the ruts because that's how he had his big crash years ago, but by doing that he struggled in the corners. He emerged unscathed and now has a real chance to win the 2020 Supercross Championship.
But not all of us have demons to exorcise. As a general rule of thumb, if the terrain is hard and smooth you will want to go softer. If the terrain is soft and rough you want to go firmer so you stay on top of the bumps.
Unfortunately, riding style, body weight, and even the make, model and year of your dirt bike plays a significant role in finding the perfect suspension setting. Don't take my word for it, test it out. Ride the same bike with a buddy and you probably won't agree on the best suspension settings for the dirt bike.
Therefore, focus on having a balanced set up by using the correct spring rate and setting the sag properly. Once you find a comfortable base setting, make small adjustments for the expected terrain.
When making adjustments, only do one thing at a time. For example, say the suspension kicks the rear during deceleration then your first step would be to adjust the rear rebound and then go ride it. Once you get a feel for that adjustment, you can change the compression to see how that affects the ride quality. Now you know why the pros spend so many hours testing. One tweak here might force a tweak there and so on until the perfect set-up exists. Then you change soil and do the whole thing again.
For more information on finding the best suspension setup on your dirt bike (and save money doing it) read Dirt Bike Suspension Setup - Save Money - Do It Yourself.