Rollout or rollout allowance is an adjustment in timed acceleration runs used by North-American
drag racing
Drag racing is a type of motor racing in which automobiles or motorcycles compete, usually two at a time, to be first to cross a set finish line. The race follows a short, straight course from a standing start over a measured distance, mos ...
and enthusiast magazines to create approximate parity over time between historic
0 to 60 mph
The time it takes a vehicle to accelerate from 0 to 60 miles per hour (97 km/h or 27 m/s), often said as just "zero to sixty" or "nought to sixty", is a commonly used performance measure for automotive acceleration in the United ...
and 1/4 mile acceleration times and those measured today using the
Global Positioning System
The Global Positioning System (GPS) is a satellite-based hyperbolic navigation system owned by the United States Space Force and operated by Mission Delta 31. It is one of the global navigation satellite systems (GNSS) that provide ge ...
(GPS).
Historically, light gates were used at the beginning and end of acceleration runs. These measured the end of runs accurately, but only began timing once a vehicle began to move (enough to trigger the light gate). Since this was the standard method, published acceleration times reflected a consistent "
rolling start
A rolling start is one of two modes of initiating or restarting an auto race; the other mode is the standing start. In a rolling start, the cars are ordered on the track and are led on a certain number of laps (parade or caution laps) at a prede ...
" inaccuracy across races, records, road tests, and enthusiast magazine reviews. Since the error was impossible to eliminate and applied to all vehicles in all timed runs it was simply ignored as a "net wash".
It only became an issue with the advent to modern GPS, which records a speed run from a standing start. To create parity with the historic method (and historic record), a convention evolved in North America to approximate the rolling start by subtracting the time it takes for a vehicle to cover its first from total recorded elapsed time.
Further reading
*
*
*
*
*
References
{{reflist
Drag racing
Measurement
Car performance