Practice Tree guide
Drag Racing Reaction Time Explained
What the number on your slip means, why .000 is perfect and anything under it loses, and how to practice a better light for free.
What is reaction time in drag racing?
Reaction time is how long after the green your car leaves the stage beam. A .000 light means the car left the beam exactly as the green came on. Anything under zero means it left before the green: a red light, and the round is lost.
Some timing systems print a Sportsman tree light from the last amber instead of the green, so a perfect light reads .500. The Practice Tree measures from the green, so .000 is perfect on both trees.
Your reaction time on a slip is not just your hand or foot. It also includes rollout, the time the car takes from your release until it clears the stage beam.
How do Pro and Sportsman trees differ?
On a Pro tree all three ambers come on together and the green comes 0.400 s later. On a Sportsman, or full, tree the ambers come on one at a time 0.500 s apart and the green comes 0.500 s after the last. The same racer will leave differently on each, so practice the tree your class runs.
| Tree | Ambers | Amber to green |
|---|---|---|
| Pro | All three at once | 0.400 s |
| Sportsman (full) | 0.500 s apart | 0.500 s after the last amber, 1.500 s after the first |
What is a good reaction time?
A perfect light is .000. In bracket racing a light in the .0s is a good light, and doing it every round matters more than one great light. Watch your average and your red-light rate, not your best.
How do reaction time and the dial work together?
In bracket racing your reaction time and how far over your dial you ran both count. A .010 light and a pass .010 over dial is a better package than a .002 light and a pass .040 over dial. Running under your dial is a breakout, and it loses unless the other car red-lights or breaks out by more.
Dial-in mode on the Practice Tree gives every rep a simulated ET against your dial, so each rep is called Won, red light or breakout.
Why is my practice light different from the track?
Mostly rollout. Set the tree’s rollout to what your car does. Staging deeper or shallower changes rollout at the track, so stage the same way every time.
If you race with a delay box, set the same delay on the tree. The delay box guide shows how to work out a starting number.
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 is a perfect reaction time?
A .000. The car left the stage beam exactly as the green came on. Anything under zero is a red light.
Is a red light always a loss?
If only you red-light, you lose the round. If both cars red-light, the car that left first loses.
Does rollout count in reaction time?
Yes. The timer starts at green and stops when the car clears the stage beam, so rollout is inside every reaction time on a slip.
How can I practice reaction time at home?
Use the free Practice Tree. Pick a Pro or Sportsman tree, set your rollout and delay, and it shows each light to the thousandth with your best, average and red-light rate.
What else helps on race day?
Next read: How to Set a Delay Box for Bracket Racing. Check the air with the free density altitude calculator, and let the Race board predict your ET for it.