Apex Ace Achievement
Earn 300 perfect Turn scores
A Perfect Turn rating is obtained when you maintain a high average speed through the entire turn, complete the turn without touching any other vehicles, and without leaving the track. You can touch rumble strips and there are a few rare corners where you can have a tire leave the track slightly without penalty, but those are rare. The speed involved varies based on your vehicle and the individual turn. If you come close to the speed required, you will get a Good Turn notice on your screen. Generally speaking, you will want to use geometric apex cornering by following the racing line, braking before the apex and accelerating after the apex.
Geometric apex cornering is where you start on the outside, braking and moving to the inside as you turn until you are on the inside edge of the track at the midpoint of the turn, at which point you start accelerating and moving back to the outside edge as the turn completes. This is the basic concept of apex cornering that many racers use and that the racing line encourages. It is great for when there are a series of turns in a row, and reasonably easy to learn (especially with the racing line on full). There is an excellent tutorial on geometric apex cornering available at drivingfast.net, complete with diagrams for those who prefer pictures.
If you have the full racing line on, these are much easier to obtain as you have more information about which vector you should be on when entering a turn. You also may want to turn the braking assist to Assisted as this will help ensure you brake on time and let go of the brakes before you slow overly much.
Most full circuit tracks have 15-20 opportunities to earn this per lap, although some turns are linked in groups of 2-3 turns rather than being scored individually. Traffic around you can impede your ability to get a Perfect rating, but on the flip side if you have a fast car with a lot of grip you can sometimes take the outside path around traffic and still get a Perfect rating.
You can track your progress on the stats screen under player info. Given that you have the opportunity to earn several thousand of these in the Career, as long as you are focused on following the racing line in corners you are likely to obtain this just as a natural part of your Career progression. If needed, it can be boosted on any track with one Drivatar or in a private match with a friend. If you are struggling with the Perfect turns, you can adjust your upgrades and tuning on the car to have more downforce, which should help.