To unlock this achievement,you have to create a car tuning file for your car.This is real easy to do, just follow these steps and you will have unlocked this achievement.
1.From the main menu, select "play career"
2.scroll down to upgrades.
3.select tune setup.
4.Then modify anything to the car.
5.Then press A (apply)
6.Select save current setup
7.Then select an empty slot and save it.
Now the achievement should be unlocked.