The Art of Road Racing
winning insights for club racers

Predictive lap timers

Two tools are especially important in developing your driving skills. Most important is video, which is the subject of a separate article. The next most important tool is predictive lap timing.

Consider you are out there on track, driving like hell, and you are trying to improve your pace. The tires are screeching, you are working the wheel, and your right foot hurts from how hard you are pressing the gas pedal. Your lap times give you some feedback about how you are doing. But how do you know whether to use 2nd or 3rd in a turn? Or whether you are currently on a hot lap? The driver’s subjective impressions are notoriously unreliable. This is where predictive lap timing comes in.

Watch this video in full screen. (Queue up to 4:10 for the start.) Notice the timer with the red numbers. The top number has a decimal point and is sometimes positive, sometimes negative. This is the delta time. Negative is better. The bottom number is the speed in MPH. When passing S/F, the upper time briefly changes to display the lap time.


What is going on here? The delta time is like the ghost car in the driving simulator. If the ghost car is ahead, then you losing compared to your previous best lap, and you should be working to catch up to the ghost.

Similarly if the delta time shown is positive 0.25, that means that you are a quarter of a second behind your best time, and if you don’t lose any more time, your final lap time will be a quarter of a second longer than your previous best. On the other hand, if the delta time is negative, -0.50, that means your lap time will be a half second lower. The time accumulates during the lap as you improve or slack. The idea is to keep seeing negative numbers, as that means improvement.

With this tool, you can see that you gain or lose time exactly when it happens on track. Thus you get immediate feedback, and you can decide to repeat a new technique on the next lap, or revert back to your previous technique. In this way you can work to ratchet down your lap times during a session.

The MPH display on the second line is helpful too. I use it to monitor my min speed in momentum corners and exit speeds. I also use it to choose gears.

While many data acquisition systems support predictive/delta lap timing, I am especially fond of the Rumblestrip Racing DLT1-GPS shown in this video. The large digits in the display allow the timer to be seen in your videos, which is helpful for analyzing your driving, especially when you are working with a coach.

Rumblestrip Racing DLT1-GPS