Practice Tree guide
How to Set a Delay Box for Bracket Racing
A delay box lets you leave on the first amber and still have the car leave the beam at green. Work out a starting number, then practice it on the free tree.
What does a delay box do?
A delay box sits between your transbrake or line-lock button and the solenoid. When you let go of the button, the box holds the car on the line for the time you set, then releases it.
On a Sportsman tree the ambers come on 0.500 s apart and the green comes 0.500 s after the last one, so 1.500 s pass between the first amber and green. Leaving off the first amber gives you one fixed cue to watch, and the box covers the rest of the gap.
How do I work out a starting delay?
Three things happen between the first amber and the car leaving the beam: your own reaction, the delay, and rollout. For a .000 light they add up to the 1.500 s from first amber to green.
So the starting delay is 1.500 s, minus your reaction to the first amber, minus your rollout. For example, if you let go of the button 0.200 s after the amber and the car rolls out in 0.300 s, start with a delay of 1.000 s.
delay = 1.500 − your reaction − rollout
How do I adjust the delay?
Every 0.010 s of delay moves your reaction time by 0.010 s. A red light by .012 means add about .012 of delay. A .030 light means take about .030 out.
Change one thing at a time. If you move the delay and your staging depth on the same pass, you cannot tell which one changed the light.
Can I use a delay box in my class?
It depends on the class. Many bracket classes allow electronics like a delay box, and many "no box" classes do not. Check the rules for your class and track before you race with one.
How do I practice with a delay on the Practice Tree?
Open Settings on the tree and set Reaction Time Delay anywhere from 0.000 to 2.000 s, then set your rollout. Hold the button, let go on the first amber, and the tree adds the delay and rollout to your light the way the car would.
Which settings can I try right now?
Each link opens the free Practice Tree already set up. No account needed.
What do racers ask?
What delay box setting should I start with?
Start from 1.500 s minus your own reaction to the first amber minus your rollout. With a 0.200 s reaction and 0.300 s of rollout that is 1.000 s. Then move it by what your lights tell you.
I red-lit. Do I add or take out delay?
Add delay. The car left too early, so it needs to wait longer. Add about as much as you were red: .008 red, add about .008.
Does rollout change my delay?
Yes. Rollout is part of the time between letting go and leaving the beam. More rollout, from staging shallower for example, needs less delay for the same light.
Can I practice a delay box without a car?
Yes. The free Practice Tree has a Reaction Time Delay setting from 0.000 to 2.000 s. It runs in your browser and in the iPhone and Android apps, with no account needed.
What else helps on race day?
Next read: Drag Racing Reaction Time Explained. Check the air with the free density altitude calculator, and let the Race board predict your ET for it.