Playing very fast cymbal crashes is possible if you learn how to do the Multi Flap Stroke. The Multi Flap is a technique name coined by Frank Epstein in his book Cymbalisms and is very effective.
To execute this technique you hold the left cymbal still and vertical. Place the bottom of the right cymbal against the bottom of the left and while hold the right cymbal strap about a half inch back from the bell of the cymbal you do a knocking on a door motion with your right wrist.
Practice playing quarter notes at 120 beats per measure and then double your playing to the eighth notes. Once you’ve got the hang of it you can play your crashes faster and faster with very little effort.
If you try to play fast like this but without this knocking technique it will be very difficult.
Remember: When you need to play fast things use your small muscles like your wrists. They can move faster and for longer without getting tired.
Try this technique the next time you are practicing the cymbal part from Tchaikovsky’s 4th Symphony, the 1812 Overture, or the Overture to William Tell by Gioacchini Rossini.