For this Achievement, you will need to complete the "Full Throttle" Challenges on following Tracks:
Full Throttle 1 - Greenhorns Grove - Waterworks
Full Throttle 2 - Urban Sprawl - Skyscraper Showdown
Full Throttle 3 - Rainforest Rumble - Tropic Storm
For beating the Challenges, you must drive and complete the whole Track without using the Brakes
and the whole Time hold RT down for full Throttle.
Full Throttle 1 & 2 are easy. The hardest Challenge is Full Throttle 3. I use the Baggie Bike here, because for me it so much easier with this Bike as with the Roach or Pit Viper. If you use the Baggie, you will earn the Baggie-Wash Challenge too.
In the last Part of the Track, you "need"flipping, i tried so many times other Techniques and tactics
but the only one he works is flipping (for me)
The Flipping is really frustrating because in 95% all attempts it fails. So try your luck and do not give up.
It works and it's only a matter of time.