NASCAR Heat 3

I used the dirt track ELDORA, was 100 laps at 100% track length.

To get 100% track length races you need to go into settings and change the Race Length to 100%.

There is no option to disable tire wear, so the lowest option is Normal.

I still had trouble from laps 85 - 100 with tire wear. I was whipping around the track most of the race and wearing my tires down. After about 85 laps the tires were really slick and hard to keep control. I spun around a few times.

I put the AI Difficulty on Auto (Easy), so after 85 laps I had lapped the pack about 5+ times and was still able to win it to get both the achievements win a 100% race length and complete a 100% race length race.

100 laps took anywhere between 20 - 30 minutes.

Fastest way is to race a dirt track. Pick one you feel comfortable with and once the race is over the achievement should pop.