Forza Motorsport 6

Yay, another solution -- I did a video and wrote up the technique though, hope it helps someone.


This shows how to get A LOT of Perfect Drafts. This is specifically for the following achievement:
Dirty Air 15G - Get 100 Perfect Draft Scores
Following this guide will allow you to get them quickly, in one showcase race: Daytona (30 laps). You will also unlock the In The Draft Platinum NASCAR badge in the process (shown in video @ 0:24), which you can equip to also get the following achievement:

FYI, completing this showcase alone is also enough to net you the following achievement:


Technique:
0. Choose NASCAR Showcases and pick Daytona, you can verify it's the right one because it will be 30 laps
1. Set Drivatar Difficulty to Average or Above Average -- anything below this will make it difficult to keep a car in front of you
2. Work your way toward the top, this can take a few laps. Don't worry, there's plenty of laps even if it takes you 5+ laps.
3. Get behind the 1st car and feather the accelerator. The main thing is to be squarely behind the 1st car, not too close, not too far, as shown in the video. It's not too hard, after a bit of practice in a few laps you will even be able to get perfect drafts while cornering. Distance should be 2-3 carlengths back, reference video for example.
4. You should aim to get at least 10 drafts per lap. Don't worry if this is not happening in the beginning, it will take a few laps of practice once it's just you and the #1 car in front of you, but at 10+ Perfect Drafts per lap, you only need 10 laps to get this.
5. Once the "In The Draft" Platinum badge pops, you're done. The "Dirty Air" achievement doesn't pop until you finish the race, but you can go ahead and take the #1 position and just race to the end in 1st place.

heres a video of how i did this achievement...super easy

I completed the achivement by running the Strictly Stock At Daytona Showcase Event.

30 laps of Daytona Intl Speedway Tri-Oval

Basically draft the cars as much as possible Over the 30 laps
4x Perfect Drafts every lap will easily give you 120 Drafts.

You only need 100 Perfect Drafts to make the Dirty Air Achivement pop

This solution is not to undermine PJTierney solution, but to give a bit more depth and detail on how to gain the achievement from my experience.

I've experimented with a few options to gain a perfect draft in this expansion update. The P Class cars worked for me, X and R Class cars didn't. I haven't tried the lower class cars, therefore I can't comment if those work to gain the achievement.

The set-up is not of significant importance, other than racing with a P Class car. You can do this in free play, career, or multiplayer modes. Best tracks to do this on, are the ones with the long straights i.e. Daytona Tri-Oval, Indianapolis Speedway, Road America East, etc.

It does seem to take longer than 2 seconds for a new perfect draft to register. Once in the slip stream (you'll know - the controller will vibrate) the perfect drafts chain together pretty quickly. The perfect drafts don't count towards your stats until the end of the race, therefore make sure you complete the race. Once I got the 100 Perfect Drafts the badge popped up, but the achievement only popped when I finished the race.

Once you have the badge, you can equip it and this will give you the 'Geared Up' achievement.

There is no question that Turn 10 has seriously hosed the drafting mechanics of Forza Motorsport 6 with the Nascar expansion. Prior to this I was getting Good drafts all the time and Perfect drafts pretty often. Since then however, I finished the entire Nascar module (minus the endurance showcase) and an entire volume from the core without getting any draft whatsoever except for a single Perfect on Homestead. And there have been lots of times when I knew without doubt from the distinctive feel that I was right in the sweet spot for maybe 10 seconds in a row while advancing on the car ahead with not one single draft awarded. To this day I have not achieved a single "Good" draft since Nascar was added, only the VERY occasional Perfect draft unless I am specifically working on drafting.

That said, you can still get this achievement if you work at it. The trick seems to be to focus on the ovals, as many have said. The Daytona Tri-Oval is a good one, but the Indy Brickyard is OK too. Homestead might be a bit short... You can do it but the straights are so short that it's hard to build up a good series of drafts before the turns, which often mess you up.

You just have to ride the bumper of the car in front of you while the two cars are perfectly square in series. And I do mean RIDE the bumper. I was only able to get the Perfect Drafts to start popping at the point where I was actually touching the car in front of me. After that initial draft there starts to be a little leeway so that you can back off a foot or two and they will continue to pop every second or so. Get more than a couple of feet back though, and the drafts will stop popping up. However, as long as you stay within 3 or 4 feet, it seems like if you make up the difference and they will start again.

Like many other solutions I managed this at the Strictly Stock At Daytona NASCAR Showcase. The reason I chose to do it in this showcase is that Daytona is a pure 100% acceleration track, you have no need to brake so you don't need to start catching the car infront after a braking point (Drafts are only awarded once you are behind a car and going faster then them and are relatively close to them).

First I equipped a +Power mod, despite starting far down the grid it only took a few laps at most to get to the front.

From their slot in behind 1st place and push, yes push them, I would push them mostly down the back straight. You can push them in the corners as well but you need to be careful to not spin them so I would back off in the corners and still get the occasional draft. One other problem with pushing them in the corners is that the AI mostly runs a very high line around the corners and it can be difficult to turn if you're pushed right up behind them and you may end up hitting the wall.

in the end it only took me at most 10 laps doing this to get my remaining 75 Drafts but your experience may vary depending on many factors.

The achievement pops after the race just before the credits and experience come up.

For me personally I found using the Nascar stock cars on the Daytona tri-oval track has worked wonders for getting drafts. It does seem a little harder than it used to be to get perfect drafts. What I did was get in position behind another car, about 2-3 car lengths and you will start to feel a rumble when you know you are catching the air draft off of the other car. Once I got that, I stayed behind the car and the rumble went away, seeming to note that I was close enough to be in the slipstream. Once I was in that position, I would get 7-8 perfect drafts on the straightaway then it was a little tougher to keep in the slipstream as I went around the corner so once I got back to the straightaway. I repeated the process, and got 7-8 more the next time, and I would just repeat the same thing throughout the race. It seemed to be the easiest way for me to get these drafts in the Nascar expansion itself.