This is best done after getting 100% in Story Mode.
You have to use single races to get these two achievements -
There are more tracks than vehicles, ensure you do a vehicle/track and win at a time until you have both of the above achievements. Then you should only have a few more races to complete. Just run the 4x4 club circuit in a fast car. It's only 2km and takes just over a minute. Obviously change the settings to easy and 1 lap.