It does depend on what mode your playing. Setting the ai is trial and error. But what you should be looking for is to set the ai difficulty in relation to where the team your driving for is in the rankings.
for instance team is Ferrari look at your teammates laps times on medium tyres during practice. For every second he’s faster than you reduce ai by ten and for every second your faster increase by ten. Then slightly adjust to suit yourself. If you want to be faster decrease ai by a couple off points
