Full list of all 15 Cars achievements worth 1,000 gamerscore. It takes around 6-8 hours to unlock all of the achievements on Xbox 360.
Successfully complete all levels of Tractor Tipping
Win the race by finishing in 1st place
Collect all available postcards in Postcard Hunt
Successfully complete all levels of Sheriffs Hot Pursuit
Complete necessary activities to unlock Tailfin Pass
Complete necessary activities to unlock Ornament Valley