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Beard's Reaction Time Clinic

Disclaimer: While based on facts about drag racing, this page contains the personal views and opinions of one racer - Michael Beard

In order to get good reaction times, we must understand the drag racer's worst enemy (besides himself), the Christmas Tree. It seems simple enough, but the starting line is often the bane of many a would-be racer. You should be comfortable with the reaction times before you worry about Top-End Tactics. Let's take a look at the anatomy of the tree, and then we'll take a look at the starting line to see how the two interact with each other, and with the driver and his car.

The tree is made up of three major parts. At the top of the tree, you see two sets of double yellow bulbs for each side of the tree (each lane). The top set is called the Pre-Stage bulbs. This is an indicator for the driver that he is approaching (and near) the starting line. The second set is called the Stage bulbs. They indicate that the driver is actually on the starting line, and presumably ready to race.

The next section is the three amber starting signals. In most bracket racing classes and Sportsman classes, these bulbs will light in sequence, a half-second apart. This is called a Full Tree. Some classes, however, use a Pro Tree. A Pro Tree will light all three ambers simultaneously, with a four-tenths of a second delay between them and the green light. We will concentrate just on the workings of the Full Tree.

The last two lights then, of course, are the green and red lights. The green will come on after the amber bulbs if the driver has not left the starting line too soon. Leaving the line before the green light will result in the dreaded red light... a foul start.

As we said earlier, a Full Tree counts down at half-second intervals. The cycle goes: Amber on, delay, amber off and next bulb on. Here's the important part. The reaction timer starts when the third amber comes on. Since there is a half-second (or .500 seconds) delay until the green light comes on, a .500 reaction time is perfect. (In the same way, the four tenths delay of the Pro Tree makes a .400 a perfect light on that one) Now, the reaction timer stops when the car leaves the starting line. To understand this better, we must examine the starting line, and how it relates to the Tree.

The Starting Line

The starting line is composed of two pair of photocells, one for each lane. The photocells detect your car when your tire interupts the light beam that crosses the lane. Tracks used to use bright lights and photocell receivers, but now many tracks are using the Compulink timing system which uses infrared beams. These beams are much better for drag racing. Drivers used to paint their wheels or put shoe polish on them to dull the bright, reflective surface. The old lights and photocell combination would sometimes pick up reflected light from the wheel, and then not "see" the tire. The infrared beams have no such problem. The timing system down the track uses a system of beams and reflectors, too. When the beam is complete (ie, the beam is reflected back to its origin), nothing is blocking it. When the cycle is broken, the beam has been interupted, and thus a tire has been sensed.

The two photocells are linked to the Tree: the Pre-Stage, and the Stage lights. When the car inches forward and blocks the first photocell, the Pre-Stage light comes on, indicating that the driver is close to the starting line. Most tracks have a rollout, or distance between the Pre-Stage and Stage beams of 6-8". The driver can now nudge the car forward until the car blocks the Stage beam, thus lighting the Stage bulbs on the Tree. This means that the driver is on the starting line, and is presumably ready to go. The driver also has the option of deep-staging, however, which means he bumps his car forward even more until the Pre-Stage bulb goes out. This means that his tire has just left the Pre-Stage beam.

Let's go back to the Christmas Tree. We said that each light was a half-second apart, and thus a .500 light was a perfect reaction time. The reaction timer starts when the third amber lights, and stops when the car's tire leaves the starting line (ie, stops blocking the Stage beam). How does deep-staging affect your reaction times then?

This question leads us to rollout. Rollout is the distance that your tire has to travel to exit the starting line. The starting line beams are about an inch or two off the ground. If you measure your tire width that far above the ground, you will find that it is about 11-14", depending on your tire height. Let's say it is twelve inches. This means that your car has to roll forward an entire foot before the reaction timer stops. This has two effects: 1) You must react before you see the green-light, and 2) Your car effectively has a rolling start of one foot before the reaction timer stops, and the ET timer begins.

Apply this knowledge to deep-staging. What effects does it have? First, what is your rollout? Your tire is in front of the Pre-Stage beam now, so a lot of your tire is 'hanging out' in front of the Stage beam as well! This is distance that the tire does not need to pass through the starting line, since it is already past it. Therefore, your rollout has decreased. What is your new rollout? Let's figure it out. How much of your tire is before the Stage beam if you have the same tire as before? If the distance between the Pre-Stage and Stage beams is 8", then your rollout is 8"! What if you have a Monster truck tire, and you are deep-staged? Think: all the extra tire is still in front of the Pre-Stage beam, and therefore is in front of the Stage beam. Your rollout is still 8"! In short, since you have less rollout, it takes your tire less time to leave the starting line, and so your reaction times will be faster. By the same token, however, you have less of a rolling start, so your ET will be slower than if you had staged normally.

You may still be wondering why you have to react before the green light comes on. The answer comes in two parts. First, as we just mentioned, there is the rollout of the vehicle. Let's use Frank Hawley's terms, and call this Vehicle Reaction time, or VRT. That's not all, though. You also have a reaction time as a human. If someone snaps his fingers in front of your eyes, how long does it take you to react? Through experimentation, both in my college physics lab, and with the practice tree, I have determined that human reaction time is roughly .21 seconds, plus or minus several hundredths for individual differences, and human inconsistency. Thus, we must also consider Driver Reaction Time, or DRT.

Armed with these two concepts, we can analyze how we have to look at the Tree. Rollout will vary between race cars, because of tire sizes and the speed of the car, among other variables. If we take my Heavy Eliminator car as an example, we'll see how our minds have to work. Through experimentation with the practice tree, I have determined that the rollout of my Duster is about .32 seconds. In this example, I will use that and the Driver Reaction time figured above.

If the driver reacts the very instant he sees the green light, what will his reaction time be? The green light comes on at .500 seconds on the reaction timer, so we have:

	Green Light:  .500
	        DRT:  .210
        +	VRT:  .320

The best reaction time our driver will get is over a second! This will certainly put him on the trailer early. Let's use a different light as a signal. The next logical choice is to use the third amber.

	  Amber III:   .000
		DRT:   .210
	+       VRT:   .320

Hey, that's a pretty good reaction time... but how do you get a quicker reaction time, or even a red-light? We have been assuming that our minds filter out other signals. If there were only one amber, with no previous signals, a .530 light would indeed be the best our driver could get. That isn't all he sees, though. He also sees the first and second amber, which makes (or allows) us to anticipate the third light, whether we realize it or not. I am lucky in that my mind seems to assimilate the first two lights in such a way that I anticipate the third bulb by .01-.03 seconds faster! This allows me to hit fairly consistent .5-oh and .5-teen lights. A little more talent, perception, and/or tuning of the car may be needed to change the VRT and DRT for drivers that react differently, or for faster or slower cars, etc.

(Boldface words are included in a quick-reference guide)

Copyright 1996-1999 Michael G. Beard

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