If you lock up the rear tire, you should keep the rear wheel locked up and ride the skid/slide to a stop. As the rear tire breaks traction (starts skidding) the backend of the bike often times will actually try to “pass” the front. This is because the front of the vehicle is actually stopping more quickly than the rear of the vehicle (if the front brakes are being applied). This causes a slide. A tire in a skid/slide has significantly less traction than a tire not sliding/skidding.
Reducing the braking force being applied to the front brake in a rear end slide situation will help bring the rear tire back into alignment. Unfortunately, this is not always possible especially if in an emergency stop situation.
That means you need to continue to apply the front brakes to slow your forward momentum yet continue to ride out the rear end slide. If you let up on the rear brake and the rear tire is not directly lined up behind the front tire you could get to experience a high-side.
What’s a high-side? A high-side occurs when the rear of the bike regains traction when in a slide. The regaining of traction can create enough torque to actually throw the rider and motorcycle in the air.
For additional information on braking refer to James R. Davis’ excellent articles (http://www.msgroup.org/articles.aspx).
For questions, comments, or suggestions on safety tips please contact Rob 'Throttle' Capozzi.