View Full Version : Explain the reaction time to me please...

08-29-2005, 05:39 PM
Can someone explain the RT top me? My understanding is that the ET doesn't start until the car moves, so I get that part, if I am not mistaken.

I want to know when does it start, and what is a good RT for an occasional trip to the track?

Is it .500, meaning that you can't leave more than .500 after the green? Or before the green???

Thus .501 redlight, and .500 pefect?


08-29-2005, 07:09 PM
You are correct as it is when you leave and has no bearing on your ET. You could set for a full minute before you left and still run 14 second 1/4 mile ET.

What the .500 or .400 (mostly pro-trees) number means is that there is that number of seconds between when the bulbs are lit. So the first yellow is lit and then .500 seconds later the next one is lit.

What is perfect semi depends on how your track shows your light. If you are running what is called a sportsman tree, where each light is lit one after the other, then it's a .500 tree. Your track may show perfect as either .500 or .000. If .500 then anything .499 or faster is a redlight. If its .000 then any negative number is a redlight. If you get a redlight that means you left before the green bulb was lit.

Clear as the great Alabama clay mud?

09-13-2005, 11:23 AM
How does "dial in" work though?

Ira R.
09-13-2005, 11:39 AM
Unrelated to the RT question. Your dial-in time is what you think the car will run. It is you telling the track that this is the time you think the car will run. If you dial in a 14.1, and run faster then a 14.1 you "break out" of your bracket, or ran faster then you said you would and you lose.


XR7 Dave
09-17-2005, 10:54 PM
There are two types of tree timers. Sportsman and Pro. Sportsman has 3 yellow and one green. All lights countdown on .500 second intervals. On the Pro tree all three yellows light at the same time and there is .400 seconds between the lighting of the yellow and the green. For our purposes we will discuss the Sportsman tree.

When the last yellow light illuminates, a timer begins and .500 sec later the green illuminates. This timer runs until your front tires leave the final staging light beam.

So, if you think carefully about this, you will realize that how you align your car in the lights and how long it takes for the front tire to roll out of the staging lights determines the beginning of your timed run. Your timed run begins when the last staging light re-acquires (yes it ignores your back tires).

So to get a perfect reaction time (not beating the green) you must leave the staging light beam at the exact moment that the green comes on. Since you have a reaction time and the car has a reaction time, and a certain amount of roll-out must occur before the staging beam re-acquires, you must anticipate the green and leave while the yellow is still very much lit.

In bracket racing you guess what time you think your car will run. If you do in fact both run your exact times, then the win or lose will be determined by the best reaction time. So it is totally possible to run slower than your dial in and still win. In fact that is usually what happens as most people have poor reaction times.

IMO heads up racing is much more fun. In heads up racing this is how it goes. One person is faster. The faster person has to think "Well, I don't want to red-light against a slower car, that would be tossing away a win. But on the other hand, if I'm too slow at the light I could get beaten by a slower car." The slower person will think " I have nothing to lose. I can't beat him on horsepower, so I'll have to take a chance at the light, try for that perfect .500, and give every last ounce." Much more thrilling than bracket racing.


09-18-2005, 12:45 AM
Except with the new light system you now show a .000 for a perfect light

XR7 Dave
09-18-2005, 04:48 PM
Except with the new light system you now show a .000 for a perfect lightYes, this is a very good point. Most tracks are using the newer software which prints out the reaction time in reference to the green rather than the last yellow. This is a little confusing at first but the process is the same.