Trail braking: basically applying the front brakes deeper and later than mere mortals all the way to the apex of the corner. But here's the catch: as you're approaching the apex and lean angle is increasing, you HAVE TO START LETTING OFF THE BRAKES GRADUALLY. Gradually is the key because letting off too fast will upset the chassis and disrupt any available traction. Also, too much braking will decrease your front tire's ability to have traction and brake under those conditions, causing the front end to TUCK: or the handlebars to turn completely flush to the apex and lowsiding. Obviously, a new tire is better for trailbraking vs an older, worn tire with a lot of laps completed.
Street riders should NEVER practice this on the road (unless your name is Lamb
). It's mainly a technique used by trackday and roadracers to keep corner speeds high and getting through the corners as fast as possible. I use this technique 100% of the time at the track. I can shave off tenths of a second to 1 sec the better I apply this technique.
Now...Trail braking is also used with "backing it in" where the rider applies heavy braking combined with engine braking/slipping the clutch for rear wheel modulation. You'll notice the rear end "steps out" towards the outside of the corner. This style helps to square off the corners better, allowing quicker throttle application. I'm currently working on this technique but can only use it in certain turns (i.e. Turns 1 and 3 at Willow Springs Big track) where it's feasible. This technique can actually make or break your lap times.