Project Cars

I won this achievement in a Solo race. On the first lap the AI cars had an accident and one car ended up in the pits. By the second lap this car was still in the pits, and the cheev popped for me.

The track that I won this on was one of the Sonoma tracks.

EDIT: I am adding to this solution to be a bit more constructive, and also explain how to net a couple of other achievements at the same time.

I had setup a Solo race on Sonoma short. The race was set to 15 laps (in hindsight, this all could have been done in 10 laps). I turned qualifying on, and had 5 opponents, set to the easiest difficulty. Also ensure that Full damage, Mechanical failures and the Tire wear options are on.

After qualifying first by about 20 seconds (was driving an RUFGT8), we began the race. I lapped the field after the sixth or seventh lap. Towards the end of the eighth lap I pitted, then resumed the race. When the race finished another achievement popped too.

I believe that you should be able to get the following four achievements (I already had two unlocked):
1) ON YOUR LEFT 20G (lapping an opponent)
2) REQUESTING FLYBY 10G (pitting while in first and resuming still in first)
3) GRAND CHELEM 20G (get pole position, fastest lap and win while leading each lap)
4) GLADIATOR 10G (won a race weekend w/full damage, mechanical failures & tire wear)

If Gladiator & Grand Chelem cannot be won on the same race, let me know and I'll edit.

I won this achievement by the career mode first champion race. just place the ai to 0 and session length to 100%. You can lap a lot of them on a 15 lap but reminder it won't unlock if it is on simulated mode.