Just copied my other post with additional information:
Laptimes should be determined by magic data and performance file, not by cc-line.
It is important that the cc-line is realistic, allows smooth driving for keyboarders and also cc-cars have realistic speed in the corners.
You should try to create a cc-line giving approximately very similar gaps for each of the three intermediates between your and the cc-car's fast laps. For example, if you are 0.9 seconds quicker than the others and the track layout is regular then you should gain 0.3 seconds per intermediate - or if the laptimes are very close to each other then also the intermediate should be. Of course this may vary because often a circuit has both slow intermediates with many curves and fast intermediates with straights at the same time (for example Indianapolis or old Hockenheimring). It cannot be this exact as I have described.
To underline this I give a example of how it should not be. I experienced this already but I have forgotten at which track. I was at the same level with the fastest cc-car...so lap difference of 0.0 sec. But now look at the intermediates: Int 1: +0.6 , Int 2: -0.8 , Int 3: +0.2
These are the fastest laps and it was impossible to go much quicker...or slower ^^
In this example it means that I was much slower in Int 1, but extremely quicker in Int 2 whereas the third intermediate (Int 3) can be considered as realistic. The same situation in the race - the result: Impossible to follow and overtake the cc-cars in Int 1, but much too easy in Int 2 because they are so slow, whereas Int 3 was realistic. That 's not a good cc-line and it does not make much fun to drive as it does not provide a realistic race.
Ok, I have explained my opinion and experiences a bit detailed now
I just wanted to show that cc-line should not focus on laptimes, but on realism, 'driveability' (does this word exist? ) and similar competitiveness of player and cc-cars.
Latimes are supposed to be determined by performance files (and magic data).