Everyone was talking on here about how hard this achievement was, but it only took me less than 5 minutes to complete it. I just downloaded a tune, and I had to rewind a few times when the car snapped around on the landing of the jump before the forest, But it wasn’t too hard to take the correct line and avoid the trees, and managing the throttle so the car didn’t snap around. I just barely got the achievement, but I got it nonetheless and I didn’t find it that hard at all.
Could have just posted in the thread you were referring to
https://forums.forza.net/turn10_postst144834_-Full-of-zest--achievement-is-impossible.aspx
I got it pretty easily too. The trick was finding a tune that made the car fast enough but still drivable.