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.
Spin 1080 degrees while airborne. In any level, except for the Megaramp.
Spin 900 degrees while airborne. In any level, except for the Megaramp.
Spin 1260 degrees while airborne.
Do a 25m boardslide.
Do a 18m boardslide.
Crash a 100 times.
Spin 900 degrees while airborne.
Do a 10m boardslide.
Spin 720 degrees while airborne.
Spin 360 degrees while airborne.
Spin 540 degrees while airborne.