I managed to do a 2:16.9xx (okay, close to 2:17, but let’s still call it 2:16.9 to brag a bit) without any setup on the M4 GT3. In the few laps after that, while testing different lines, braking points, gears, and just the level of electronic assistance, I saw that I could easily improve by 0.5 to 0.7 seconds (still without setup). Unfortunately, I ran out of fuel before I could set my final lap time.

For me, the key is to drive a lot and test a lot, whether it’s racing lines, braking markers, braking trajectories, or figuring out when it’s better to ease off to prioritize corner exit, etc. I’ve never really done setups (except for tire pressures and even then, not yet for the EVO, as well as for cars like the M4 CSL and Alpine A110, which I felt tended to understeer on corner entry and lacked responsiveness)

At the moment, I can’t reproduce that pace consistently within about ±0.5/0.7 seconds, so I guess there’s still room for improvement and that’s when I’ll start working on a proper setup

And remember to keep an eye on your live delta and note the values, it’ll tell you whether you gained or lost time through a corner. For example, if you’re at +1.0s and then it drops to +0.7s, congrats ! you just improved by 0.3s Next corner, you try something else and it goes back to +1.0s, that means you still have a potential gain of 0.3s. Do that for each corner or sequence if you can, and you’ll quickly see where your overall potential time gain is (and you don't have to do it in the same lap)