The RT clock starts when the green light illuminates on the drag race tree. The time is sometimes represented in thousands of a second from the time of the third yellow light illuminating. On a sportman tree this is .500 of a second. A perfect reaction time in this case would be .500. Leaving before the green light is a foul also called a red light. For example, a time of .499 is a foul, a very close foul but still a red light and you are done for the day. Any time greater than .500 is a clean start and the race winner is determined by whomever crosses the finish line first.

Lets say that you are racing and have a reaction time of .700 while your opponent has a reaction time of .500. In this case your opponent has left and you have given them .200 of a second of head start. Why? If your car isn't more than .200 of a second faster than the other car then you will lose. The moral of the story is to avoid giving away time. Ever heard the saying, "Snoozers are losers"?

RT is the total of Human Reaction Time (HRT) and Vehicle Reaction Time (VRT). HRT in drag racing is the time that it takes for a driver's eye to recognize some event and to signal the brain to control the foot to lift off of the brake pedal (we're talking about foot brake racing here).  Notice that we didn't mention what the eye event was yet. Also note that we're talking about reacting, not thinking which would be too slow.

VRT is the time that it takes for the vehicle to start moving from the time that the brake pedal has been lifted. Again the car has been held in place by foot braking. A car weighs a few thousand pounds and it takes a fraction of a second to get everything moving. Or more correctly accellerating to the point that the start clock begins. The distance depends on the size of the front tires and is approximately seven inches. This also depends on how far forward the driver positions the car after lighting up the staged lights.

A typical street car will have a VRT in the range of .3xx seconds. That time will be fairly consistent depending on weight and power but may vary slightly due to factors beyond the drivers control such as track condition. In this case, going back to the RT formula a perfect RT of .500 will require a HRT of .2xx. This is within the capability of most drivers with training and practice.

What this all comes down to is that the driver has to make up the difference in the RT formula. It also means that under these circumstances the triggering eye event will be the illumination of the third yellow light. That's why the general advice given at the track is to "leave on the third yellow".

The practice tree needs two types of information which may be defaulted or entered by the user. The first is the speed of the tree, in our case we have used .500 for a full or sportsman tree. The other information is the VRT or more commonly called the Roll Out. A value of .320 is a reasonable first estimate.

The practice tree will take your HRT based on releasing a button or better yet using a pcliminatorTM Reaction Time Pedal Switch (RTPS) in your car and add the specified Roll Out displaying the total RT. This makes it easy to practice since you don't have to do the addition in your head.

In order for the practice to simulate your real track conditions and make a valid improvement you need to determine as accurately as you can the VRT.

One way of estimating your vehicle (foot brake, automatic transmission) reaction time is to videotape the car at the track. You need someone to videotape the car from behind such that the drag race tree lights can be seen as well as the car's brake lights. This method also requires that the camcorder be able to single frame through the video or download the video to a PC with video editing software.

In the U.S. the video standard NTSC uses a frame rate of about thirty frames per second (ignoring Drop Frame Mode). This means that a single frame of video from the camcorder represents 1/30 of a second. If we can capture the Drag race tree third yellow light just starting to illuminate and the cars brake light just starting to go off we can calculate the drivers HRT.

Since we are at the track and making a pass we will also receive a timeslip showing the total RT. Make sure to match the video with the timeslip correctly or the data will be wrong.

In this series of frames starting from T0 when the third yellow light has started to light up the timing will start to see how long the driver takes to react to the light and release the brake pedal. Note how the light itself takes a few frames to reach maximum brightness. This is due to the time that it takes for the bulb filament to reach maximum temperature. If the track was using LED lights then the illumination would be virtually instantaneous.

Frames T1 through T7 show no change and the brakes are still applied and at full brightness level. Finally in frame T8 the brake lights start to dim indicating that the driver has released the pedal. Note that this estimate assumes that the brake light switch will turn off the lights at or near the time that the brake has been released.

In this example the driver took 8 frames to release the brake pedal. That means that the HRT is

.593 - .267 = .326

Using the results of this example, setting a Roll Out of .320 would be ok but it could be rounded to .330 which would force a practice HRT to be a little quicker. The VRT should be checked occasionally if changes have been made to the vehicle which increase the power, weight and traction. A change of few hundredths of a second in VRT will throw off your RTs between practice and the track.