One of the principles of physics is that certain loads increase in a geometric fashion, not linear, as a function of speed. For instance (being VERY inexact) if the load on a surface is 10 lbs. when it is hit with a hammer at 10 ft/sec, that same surface will see 100 lbs of force when the hammer speed is doubled- - - - -the load squares! Now apply that to the pressure compression exerts on a piston ring- - - - -it pushes the ring out against the cylinder wall, and down against the top of the ring land below it to help the ring achieve a seal. As the speed of the piston increases, the force applied to the ring also increases, and the ring gets a better seal. Today's "low tension" rings rely almost entirely on cylinder pressure to get a seal- - - - -there's very little spring tension against the cylinder wall involved.
Jerry
