The gyroscopic effect of your dirt bike explained
There are a number of laws of physics that influence dirt bike riding. During the MXGP broadcasts, commentator Paul Malin occasionally talks about a “huge panic rev”. He is talking about the gyroscopic effect of a dirt bike and we will explain this for you.
That famous “panic rev” is not just a twist on the throttle. It's a matter of action and reaction. If you touch the rear brake during a jump, the rear wheel will stop spinning. That's the "action" part. This action causes a reaction in the part of the motorcycle attached to the rear wheel (the frame). If the rear wheel stops turning, the motorcycle frame will react in the opposite direction. That is the reaction to the action. If you apply the rear brake in the air, the front of the motorcycle will dive down. Remember that the motorcycle and rider are virtually weightless, so only a small amount of force is needed to move the frame of the motorcycle when both wheels are off the ground.
What if you notice that the front of the bike dips too sharply during the jump? The same rule of physics causes the front end to spin up when you open the throttle in mid-air. By turning the rear wheel faster (action), the frame reacts so that the front rises. The more abrupt the acceleration, the greater the force of the reaction and the faster the front end rises. So that is the famous “panic rev”.
The more sensitively you deal with this fact, the softer the reaction will be. By gently tapping the brake, the front of the motorcycle descends gently. By applying the brake you immediately lower the front of the motorcycle. Keep in mind that once the wheel has stopped spinning in the air, tapping the rear brake will no longer have any effect. Conversely, as soon as the rev limiter intervenes, the front of the engine will no longer rise. Also remember to pull in the clutch when you apply the rear brake in the air, otherwise you will brake your bike to death. In the video you can see a perfectly executed panic rev at 1:05 minutes.
Photos: archive
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