Drive Kick + Down Kick = Ouch

The muay thai drive kick lets you leverage you weight and momentum to deliver power. The muay thai down kick leverages torque and downward force to deliver power. Now put those two forces together and you have a strike causes serious damage. The video shows the basics of the technique, but here are the main points:

Drive kick:

• It's used to quickly deliver a muay thai round kick from a distance, covering the distance with a lateral drive.
• You still have to turn your hips over and pivot - but the pivoting takes place during the drive.
• Lean forward - keeps the momentum driving
  
• Kick through your target

Down kick:

• Drive down kicks hurt a lot more than standard round kicks, I speak from experience.
• It's slower than a standard muay thai round kick
• You have to lift your leg higher - the strike lands downward on the target.
  
• The movement of the kick takes the form of an arc.
• Rotate the hips in a downward diagonal motion
  
• When thrown against the front of the thigh it will buckle your opponent at the hips, setting him/her up for elbow strikes or knees into the high chest/throat area.

Its a subtle difference between the the drive and the down drive kick is subtle, you can only really see it by watching how the bag holder's body reacts to the impact.