Here is the full list of all 12 The Ramp achievements. It takes around 0-1 hour to unlock all of the achievements on Windows.
Spin 1080 degrees while airborne. In any level, except for the Megaramp.
Do a 25m boardslide.
Spin 900 degrees while airborne. In any level, except for the Megaramp.
Do a 18m boardslide.
Spin 1260 degrees while airborne.
Crash a 100 times.
Do a 10m boardslide.
Spin 900 degrees while airborne.
Spin 1080 degrees while airborne.
Spin 720 degrees while airborne.
Spin 540 degrees while airborne.
Spin 360 degrees while airborne.