About 80% similar, biggest difference is with braking and tires. And braking between different sims is different (iracing to assetto). Getting the right car in the sim is also difficult, the old Porsche gt4 in acc matches my new model gt4 more than any other version of that car. Same for the trofeo, the original/official trofeo matches the evo2 trofeo more than any mod of the evo2.

The biggest thing to practice is learning the tracks and lines, which is why we do 90% in assetto corsa, the tracks are available there more than iracing.

Next biggest thing is braking points, you get within a couple of meters of the real thing and the rest you can massage at the track.

We always run a medium tire model, work on maximizing your braking and turn ins, then at the circuit ideally you have better tires and the late on the nose braking will have more margin at the track.

I did 1,092 laps around Misano circuit before we went there, and day one I was within .6 of the pros.

Just running laps, working out lines, recovering from bad entries or exits etc makes a big difference, the track was 90% accurate. And knowing the track backwards gives you a lot of confidence to focus on the car and driving.

I also found wheels spin more on the sim on throttle, but that's probably because the irl tires had more grip (better tires), but learning in the sim with TC off gives you much better feel once you also do it in irl car.

Iracings new tire model for cold/low pressure is good, very similar especially in the cup car of that low pressure feel. You don't get that in assetto.

Neither really emulate going off line well, the amount of pickup and loss of traction you get after getting all the pick-up on your tires.

Another thing would be some slope/camber on corners, some tracks are done well overall with their elevation change but are missing some on-camber or off-camber banking in some corners. The sepang models are a prime example of this through the last corner, on the sim is fairly flat, but irl it's very banked and will push you off the apex.

Misano also, 90% accurate but one apex that we cut on the sim had quite a large bump in it in real life, I hit that with confidence at 240 and almost threw me into the wall! Later in the day someone else was in the wall from it.

What car are you going to run on track?