The achievement unlocks when your first fault on an Extreme difficulty track run happens between the last checkpoint and the end of the race. "Corky Construction" is the best track to attempt this on. I used the Mantis bike but the Helium is quite good on some other Extremes so it may be useable as well. It is a bit difficult to string together obstacles on this track, but that is actually helpful here since each obstacle can be approached consistently and deliberately. You must reach Checkpoint 11 with 0 faults. From there, fail to complete the last checkpoint (rear-wheel hop on barrel with blue smoke) and the achievement should pop. Below is my attempt at describing the way I was able to consistently clear each obstacle:
The first difficulty is at checkpoint 1. Come to a complete stop at the horizontal section. Do a small bunny hop from the horizontal section to the adjacent tilted section. Then, land on the tilted section in a wheelie while leaning back, and throttle + lean forward to perform a larger bunny hop to the highest section. If you get enough height you should be able to land your back wheel on the bottom of the highest section while leaning forward and throttling to make it to Checkpoint 2. If you don't get quite enough height, leaning back at the right moment can get your rear wheel up there, but then you'd need to bunny hop off of the highest section which I struggled to do consistently. It's quite a long gap, so doing a quick front-flip might save you from a sloppy high section exit. If you have to practice this checkpoint numerous times, you will probably get used to how it feels when starting from a neutral position. So, when you are stopped at the horizontal section, pay attention to whether your rider is leaning back or not when you start the jumps. Its possible either way, just pick one that feels the best and stick with it.
Checkpoint 2 is much simpler. Come to a complete stop with your front wheel near the black 2 sign. Perform a very fast, very small bunny hop to get onto the ramp in front of you. Rotate quickly so that you can land your rear wheel on the bottom of the ramp before your front wheel hits. Make sure that you are leaning back when you land, then quickly lean forward to spring up over the ramp. Getting over this spike can be tricky, but doing an endo at the top and yanking yourself over seems to be easier here than in other places in the game.
Checkpoint 3 can be easily done if you approach the initial ramp properly. Come to a stop with your front wheel near the wooden ramp and the rider leaning back. Head towards the ramp, and just when your front wheel reaches the steepest part of the ramp, lean forward. The idea is to keep the rear wheel on the ramp so that you can accelerate for the entire length of the ramp. When done correctly, you can simply drive off the top barrel while leaning forward to get to Checkpoint 4. If you don't get enough speed, you can often still do some sort of rear wheel bounce off of the barrel to get there. Stopping safely on the Checkpoint 4 platform might be the hardest part of Checkpoint 3!
Checkpoint 4 is simply a large bunny hop combined with a vertical obstacle. Familiarity with the in-game tutorials will help you the most here.
Checkpoint 5 is probably the easiest in the track. Bunny hop off the top of the ramp and lean back at the right time during the jump to make sure your rear wheel doesn't clip the explosive barrel.
Checkpoint 6 requires some faith. My method was to reverse most of the way up the hill, then lean back and floor it to the ramp. Keep leaning back and you should bounce off of the barrel and be able to correct yourself while flying to the start of Checkpoint 7.
Checkpoint 7 is so easy that I failed a few times simply because I tried to do it immediately after Checkpoint 6. Come to a complete stop right up against the wall while leaning back. Do a nice, healthy bunny hop off the ramp and then lean back (much like Checkpoint 5) so that you get enough height to drive off of the excavator bucket to Checkpoint 8.
Checkpoint 8 is similar to Checkpoint 2. Bash your rear wheel against the side of the truck cab, then endo+flap to get up onto the cab.
Checkpoint 9 is easiest if you start from the bottom of the dirt ramp. You can lean forward and roll down to get wedged between the truck and the ramp. When you start accelerating, your rider should be leaning forward, but your joystick should be neutral. After you get moving begin to lean forward just a little so that you don't flip back, but not so much that your front tire hits the ramp slowing you down. The aim is to drive up the side of the R.A.C.E. block with only your back wheel while leaning forward so that you go over instead of straight up.
Checkpoint 10 is the last you'll have to do for this achievement, and is potentially the toughest. There is a line near the start of the checkpoint; I started with my back tire here. While the rider was leaning back, I accelerated off of the first ramp. This jump requires a teeny bit of leaning input; tap to lean back only as much as necessary. You should land at the bottom of the second jump while leaning back, then smoothly perform the same bunny hop technique as in Checkpoints 5 and 7. The result should be your back wheel slamming the bottom of the overhanging barrel, allowing you to do the brake+lean forward trick to flip you to the end.
This is just my attempt at a reasonably consistent walkthrough for the easiest Extreme track. It is by no means the only way to complete these jumps. If I glossed over something important or missed an easier way past any of the obstacles let me know!