'Heel-toe' is a technique used in auto racing to allow you to downshift and brake at the same time. If you want to go fast and keep your transmission from exploding, you have to use heel-toe.
Someone once asked:
"I have a question regarding about heel toe. Is heel toe same thing as double clutch but applying the brake in the same time ??? And also whats the advantage of heel toe over double clutching?"
And I sent them this reply:
I've been told (and wonder if it's really true) that the name comes from the way the pedals where set up a long time ago. Apparently early cars had the gas pedal in the middle of the clutch and brake, so if you wanted to apply break pressure and use the clutch at the same time you had to turn your foot sideways and use the heel and toe of your foot at the same time.
Anyway, now days the brake and gas pedals are next to each other. So, if you want to apply brake and use the clutch at the same time you use the ball and heel of your right foot.
Note that there are two things going on here. One is braking and the other is down-shifting the transmission.
The goal is to down-shift the transmission while slowing the car (i.e. braking).
Older race cars (and a few newer ones :-) don't have synchronizer gears in their transmissions. This saves on weight/complexity and increases reliability (one less thing to break). Also, the gears are "square cut" which makes them refuse to shift unless the engine RPM's are correct for the the wheel speed.
So, in order to down-shift a non-synchronized transmission you need to first take it out gear, then match the RPM's and then put it into gear. You need to put the clutch in (i.e. disengage the clutch) to pull the transmission out of gear. Then you need to release the clutch to connect the transmission back to the engine and then increase the engine RPM to the correct speed. All this so you can (quickly) put the clutch back in and the shift into the lower gear. This action is known as "double clutching".
Done quickly it's -
clutch in, pull out of gear to neutral clutch out, "blip" gas to increase engine RPM clutch in, push into lower hear clutch out
So, as you can see, one will "pump" the clutch two times.
You can double clutch alone and you can brake alone, but you can be much quicker around a race track if you can double clutch and brake at the same time. This poses some problems for one of your feet, as it needs to be in two places at one time, namely the brake pedal and the gas pedal.
So, you put the ball of your right foot on the brake pedal and the right edge of your right foot is used to work the gas. If you try this in a normal street car you find it does not work - often you need to adjust the pedals to make this work well... I often bring the gas pedal "up" a 1/2 inch or so. There are also special pedals you can buy which will extend the pedal area and make it easier to hit both the brake and gas.
It's the fastest way to get a car ready for the next turn. If you are driving on a race track you may find yourself at the end of a long straight which ends in a tight right or left hand turn. You need to slow down (i.e. brake) and you also need to get the car in a lower gear once you have slowed down so you can accelerate through the turn. So, you need to brake and down-shift at the same time. Time for heel-toe...
This is just the beginning. Once you can do this you add it to all sorts of other techniques like trail braking and threshold braking. It's all about going as fast as the car will allow.