The One Foot Rollout: How American Tests Shave Three Tenths

Rollout is the first foot, 305 mm, of a standing start, and in American testing the clock does not run during it. The convention comes from the drag strip, where the timing beam sits at the far edge of the staging position rather than at the car's resting point. By the time the beam breaks, a quick car is already doing 8 to 9 km/h, and the published time is 0.26 to 0.42 s shorter than a run measured from true rest.

Why the timer starts late

On a drag strip a car stages by rolling forward until it interrupts a light beam a few centimetres above the surface. That beam is positioned so the front tyre has already crossed the physical start line, because the electronics need the car stationary and settled before the tree counts down. The elapsed time is measured from the moment the car clears the beam, not from the moment the driver reacts, so roughly one foot of travel happens before any number exists.

American magazines adopted the same reference so their figures could be compared directly with strip results. It became a house standard, it is disclosed in most methodology pages, and it is applied consistently. The problem is not the practice, it is that the headline figure never carries the footnote.

The arithmetic, and why slow cars gain more

Time to cover a fixed distance from rest is t = √(2s / a). With s fixed at 0.3048 m, the only variable is how hard the car accelerates. Because the relationship runs through a square root, halving the acceleration does not double the time inside that first foot, it multiplies it by about 1.41. The deduction therefore grows for slower cars, but grows slowly.

Two things follow. First, the commonly quoted range of 0.2 to 0.3 s is correct for performance cars and understates the effect for everything else. Second, rollout compresses the field: it takes a larger bite out of a slow car's time than a fast one's, so a rollout-timed comparison makes the gap between a 3 s car and an 8 s car look smaller than it is.

Deep staging, and the limit of the trick

Drag racers know the beam position is worth time, and some stage deeper, rolling further forward so an even larger share of the launch happens before timing starts. The gain is real but bounded: roll too far and the pre-stage beam clears, which disqualifies the run. In magazine testing there is no equivalent, because the rollout distance is fixed at one foot by the measuring equipment rather than chosen by the driver.

What does vary between publications is whether rollout is applied at all, and whether the figure quoted is a best run or an average of several. A single best run out of six, on a prepared surface, with rollout deducted, is a legitimate number and a very different one from a factory claim measured without any of those advantages.

How to spot a rollout figure in the wild

• The unit is a strong hint. A time to 60 mph almost always carries rollout. A time to 100 km/h almost never does.
• Check for a quarter mile figure alongside it. If the same source publishes elapsed time and trap speed, it is working to drag strip convention, and rollout is part of that convention.
• Compare with the factory claim. A tested time several tenths quicker than the manufacturer's own figure is usually a rollout difference rather than a heroic driver.
• Look for the methodology page. Publications that apply rollout generally say so. If nobody says anything, the figure is not comparable to anything.

The practical rule is to keep one convention for your own list. Convert everything to 0 to 100 km/h without rollout, because it is the measurement that cannot be flattered by where somebody put a light beam.

Questions readers ask

Is rollout cheating?

No. It is a disclosed, consistently applied timing convention inherited from drag racing, and every car measured that way gets the same treatment. It becomes misleading only when a rollout figure is compared directly with a figure measured from true rest, which happens constantly in cross-market comparisons.

How far is one foot of rollout?

0.3048 m, or 305 mm. It is the approximate distance between where a staged car sits and where the timing beam fires on a drag strip, and it has been carried over into road test practice as a fixed reference.

How fast is the car going when the clock starts?

Between about 5 and 10 km/h, depending on how hard it launches. A car pulling 1.22 g is doing 9.7 km/h at the beam, a car pulling 0.35 g is doing 5.2 km/h. In neither case is the measurement a true standing start.

Do European manufacturers apply rollout?

Generally not. European 0 to 100 km/h claims are normally quoted from a standstill. That is the single largest reason a European factory figure looks slower than an American magazine test of the same car.

How do I remove rollout from a published figure?

Add it back. Roughly 0.23 s for a car under 2.5 s, 0.26 s around 3 s, 0.30 s around 4 s and 0.33 s around 5 s. The correction is not exact, because it assumes constant acceleration, but it is close enough to stop a rollout figure outranking a car that is genuinely quicker.

Sources

• Rollout (drag racing), on staging beams, deep staging and the origin of the one foot reference.
• 0 to 60 mph, on how rollout is applied in road test practice and the typical 0.2 to 0.3 s effect.
• 0-60 Specs, testing methodology, on verification practice and disclosure of timing conventions.

Times in the table are calculated from t = √(2s / a) with s = 0.3048 m, assuming constant acceleration.