Here is the full list of all 48 DiRT 4 achievements. It takes around 60-80 hours to unlock all of the achievements on Windows.
Earn the Fearless Bonus in a Stage or race
Call in the Chief Engineer's recommendations during a Service Interval
Complete the Welcome Event
Triumph in the face of adversity
Finish three sectors of a Stage with a flat tyre
Cleanly land a jump longer than 65m
Earn the International Rally R-3 licence
Earn the International Rally R-1 licence
Earn the International Rally H-C licence
Earn the International Rally H-A licence
Earn the National Stadium Pro-3 licence
Earn the National Stadium Pro-1 licence
Earn the International Off-Road C-3 licence
Earn the International Off-Road C-1 licence
Get an overall win in the lowest eligible Vehicle Class in a Rally Event in Career
Qualify in the top spot in a Rallycross Event in Career
Qualify for an A-Final in a Landrush Event in Career
Finish in first place in a Career Event
Win the Global Rally Series
Win the FIA World Rallycross Championship
Win the Landrush World Series
Win the Historic Legends Series
Win the Triple Crown
Complete all of the Advanced Driving Techniques at the DiRT Academy
Own a vehicle equipped with all Grade A parts
Win your class in a multi-class Event in Career
Buy a vehicle from the Classifieds
Hire a fourth Engineer onto your Team
Complete a Stage or race with the Fearless Preset active
Win a Stage in Headcam
Complete a clean Stage or race
Get a bad case of the Mondays
Set a time in every challenge in a single Joyride Chapter
Achieve 10 Gold medals in Joyride
Set a Gold medal time in a Time Attack challenge without hitting a penalty marker
Destroy 100 blocks in 60 seconds in Joyride
Finish in the Second Tier or higher in a Daily in Community Events
Finish in the Top Tier of a Delta Daily in Community Events
Complete back to back Weekly Community Events
Complete all 12 Stages of a Monthly Event in Community Events
Complete an Event in Jam Session
Win a Stage at night
Finish a Stage in sunny conditions in Community Events
Get promoted to a new Tier in Pro Tour
Complete 25 Events in Pro Tour
Take two Joker Laps and win a Rallycross race
Repair your car on Stage and win the Stage
Upgrade three Facilities to Grade A quality