Rollout (drag racing)

Rollout or rollout allowance is an adjustment in timed acceleration runs used by North-American drag racing and enthusiast magazines to create approximate parity over time between historic 0 to 60 mph and 1/4 mile acceleration times and those measured today using the Global Positioning System (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" 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 1 foot (30 cm) from total recorded elapsed time.

Further reading

• "One Foot Rollout". Support Centre. Racelogic. 2018-08-01. Retrieved 2019-08-23. 'Rollout' is the distance travelled by a vehicle before the timing lights on a drag strip are triggered. … can affect the final run time by up to 0.3 of a second. … important to discount this first foot of movement from the final run time, to ensure that the run time captured by the GPS data logger is as close as possible to the official drag strip time.
• Webster, Larry (2005-05-01). "The Importance of 'Rollout'". Car and Driver. length of the rollout depends on the diameter of the tire and where the driver chooses to position the car at the start. Although the rollout distance is typically only a foot or so of a quarter-mile, it can affect the elapsed time by as much as 0.3 second,
• Markus, Frank; Brantley, Brian; Lutz, Cory (2017-02-20). "A Closer Look at the 2017 Tesla Model S P100D's Ludicrous Acceleration Run". Motor Trend. T= -0.26 seconds … 0.71g acceleration averaged over the first foot of travel … T= 0.00 sec … The car crosses 1-foot mark and official timing starts. The car is traveling at 5.9 mph, averaging 1.30 g of longitudinal acceleration. … T= 2.28 sec … The car crosses the official 60-mph mark
• Counts, Reese (2016-09-02). "Why zero to 60 mph performance is overrated". Autoblog. The time difference is usually due to … needless application of rollout. Rollout comes from the drag strip. When you start a quarter-mile run, the timing lights don't start until the front wheel is all the way over the starting line. … approximated by subtracting the first foot of an acceleration run. Now a common substitute is to cut the first 3 mph from a run, cutting as much as 0.3 seconds off the time. Some publications post a 0-60 mph with rollout and others do not.
• Edmunds, Dan (2008-08-20). "A Few Words About Rollout". How We Test Cars and Trucks. "shallow staging" can therefore get almost a free foot of untimed acceleration before the clock officially starts, effectively achieving a rolling-start velocity of 3-5 mph and shaving the 0.3 second it typically takes to cover that distance off his elapsed time (ET) … rollout with 0-60 times is inappropriate in our view. … begun publishing a clearly marked "with rollout" 0-60 time alongside the primary no-rollout 0-60 time so readers can see the effects of this bogus practice.