Some readers may find this surprising, but the clock doesn't start on our acceleration runs right when the vehicles start rolling. This practice, which is commonly called rollout, comes from the drag strip, where it's possible for a car to travel a foot or more before it trips the timing light that actually starts the clock. The industry standard calls for a one-foot rollout before a timed run begins. Our old test equipment couldn't measure that precisely, so we approximated a foot by beginning our runs at 3 mph. That was a fair estimate when cars didn't launch as hard as they do today, but gains in traction, launch control, and horsepower have rendered our 3-mph approximation increasingly obsolete. Our GPS-based Racelogic VBox test equipment is accurate enough to measure the first foot of rollout, so starting with the December 2019 issue, we're changing our acceleration reporting.

Tavis Coburn Car and Driver

What is Rollout?

Lining up a vehicle at a drag strip requires careful placement of the front tires relative to two beams of light. When a car's front tire crosses the first one, a "prestage" warning is lit. When the tire interrupts the second beam—the "stage beam," which is seven inches ahead—the car is staged and ready for a run. The clock starts when the car's tire moves enough to uncover the second light beam. The distance the car travels before the stage beam is uncovered (and therefore the timing begins) is what's known as rollout, and it can vary from nothing to more than a foot. Obviously, this affects the elapsed time, sometimes by as much as 0.3 second. Our testing now adopts the industry-standard one-foot rollout.

Face the Clock

Here's how our change affects the C8 Corvette. The C8 accelerates to 3 mph in 0.1 second, but the one-foot time is 0.2 second, at which point the Corvette is going 6 mph. In general, acceleration times for most cars will improve by about 0.1 second with the new procedure. In the interest of full disclosure, we'll be publishing the one-foot-rollout time of every tested vehicle so you can add it to the acceleration times to arrive at true zero-to-X measurements. We also will be recalculating times for past vehicles, so that any comparisons we make today are apples to apples. Unfortunately, it is impossible to recrunch pre-VBox test results. We will generate estimates in those rare instances.

From the December 2019 issue.

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