DiRT Showdown

For this achievement you've got to complete all 150 joyride missions, made up of:
•75 in battersea (25 in each of 3 areas)
•75 in Yokohama (25 in each of 3 areas)

Simply head to joyride on the main menu, then select which area you want to do first, then go on to complete all the missions. At 20/25 in each sub-area, the next area unlocks, but I like to do all of an area at once, so press x to bring up the mission list and finish the remaining missions. This way you won't have to back track to get missions you missed.

For completing the missions themselves, here are my tips from my othe solution:
To complete the missions, you are tasked with completing various activities, including donuts, drifts and jumps. For the jumps, I advise taking a long run up and using boost before you leave the ground. With the donuts, you need to press B to start a drift around the designated object, but keep leaning your left analogue stick towards the object and hold down the accelerator. For the drifts, just press B whilst turning to the left or right and your car will begin to drift.
There are also times when you have to spin, which is kind of like doing a donut but around yourself. Just push the analogue stick to the left or right then pull fully on the accelerator. Your car should start a spin.

Here are some helpful videos from the youtuber: 'MotoGamesTV' all credit to him, as these videos are great if you're stuck on a particular mission.

ok just to confirm i have as of yet not completed this but i do know how to complete it.
simply go into joyride, select the yokohama track and complete all of the missions that range from gathering air, drifting, donutting, spinning and driving through fences and gates.
the hardest part of this yokohama i found was drifting on top of the containers. took my at least ten tries.
repeat for battersea as it is a bit easier. the cheevos should pop for completing 100% and then the hoonigan cheevo

feedback welcome