I theory no RT wont effect et. But you can see a small change sometimes by the type of tree you run. Like running a standard bracket tree compared to a Pro Tree. RT is the time from when the green light comes on until your car moves and breaks the beams. Now on a full tree you can shallow stage as you have the time to leave a bit before the green light comes on and get some rollout in your car. In other words get the car to be moving a bit before the green comes on as you have the distance of the tire sidewall with rollout to actually have the car moving before you break the beam. So your car can be moving a tiny bit when you break the beam for a small advantage when compared to running a Pro Tree. A Pro tree is when all three yellow lights come on at the same time. And you dont have the time to launch a tad early and get the car moving a bit. And thats because as soon as you see a yellow light the green will be coming on right away so if your car does not react real fast you just dont have the time to move it fast enough to break the beam so many deep stage when running a Pro tree so you break the beam as soon as the car moves. You can get a better RT but you may slow down about 1/2 a tenth in ET since you dont have time to get the rollout of the tire sidewall and get the car moving a bit. So when running a Pro tree if your car is not set up for it and you have to deep stage as much as they allow (some turn the top bulb out if allowed) you dont get the slight rollout movement and may loose a very small amount of et. I have heard some say almost a tenth but I never tried it. If your car is set up for quick reaction then you may not loose much or any ET. But the actual reaction time will not change your et. Ron