How to Measure Your Car's 0–60 With Your iPhone

What do you need to time a 0–60 run?

Genuinely just two things: an iPhone on a recent version of iOS, and a mount that holds it rigidly. No OBD dongle, no external GPS puck, no wiring. The mount is the part people underestimate — a phone sliding around a cupholder measures the cubby's rattle, not the car's acceleration, so use a firm windscreen or vent mount and check it doesn't wobble when you tap it.

Beyond the hardware, you need the right place and conditions:

• A clear view of the sky — open ground gives the GPS a far stronger fix than tree cover or buildings
• A flat, straight, dry surface — even a gentle slope shifts the time by tenths
• Somewhere legal to test: a track, closed course or drag strip, not the public road

Why does GPS + motion sensor fusion work?

Your phone's GPS measures speed directly from satellite signals, and it is far more truthful than your dashboard. Car speedometers are legally required never to under-read, so nearly all of them over-read by a few per cent — when the needle says 60, the car is often doing 56–58 mph. Timing runs off the speedo therefore clips tenths off the true figure.

GPS alone, though, updates too slowly on a phone to resolve hundredths. That is where sensor fusion earns its keep: the iPhone's accelerometer samples motion around a hundred times per second, so an app can blend the two — GPS anchors the true speed, the accelerometer fills the gaps and pins the exact instant the car started moving. The output is a time to the hundredth of a second with a stated ± confidence band.

Dedicated GPS performance boxes — 10–25 Hz loggers costing £100–£300 — remain the benchmark hardware. But for road and track hobby use, a well-mounted phone with a good sky view achieves comparable practical accuracy, which is why phone timing has become the default way enthusiasts answer this question.

How do you run a 0–60 test?

The step-by-step sequence below covers a full run. The one thing worth understanding up front is that launch detection in PitLaunch is automatic: you arm the timer before you set off, and the app watches the sensors and captures the whole run by itself. There is no button to stab at the moment you launch, and nothing to interact with while driving — the same armed run also captures the ⅛-mile split, quarter-mile ET with trap speed, and peak G if you keep going.

One firm word on safety: acceleration testing belongs on a track, closed course or legal drag strip. Set everything up before you set off, or have a passenger operate the app, and never touch the phone while the car is moving. Obey local laws, always.

Standstill or 1-foot rollout — which should you use?

Most manufacturers don't quote a dead-stop 0–60. They use the drag-strip convention called 1-foot rollout: the clock starts only after the car has moved roughly a foot, exactly as a strip's staging beams work. Because that first foot is covered slowly, rollout is typically worth 0.2–0.3 seconds — a car that needs 4.5s from a true standstill posts roughly 4.2–4.3s with rollout.

Pick your convention by purpose. Comparing against the manufacturer's claim or a magazine test? Use 1-foot rollout. Tracking your own car over time — before and after a remap, new tyres, different fuel? Either convention works, as long as you never mix the two in one comparison.

How do you get consistent, comparable results?

A single run is an anecdote. Traction, temperature and gradient all move the number by tenths, so treat every session as a set and control what you can:

• Run at least three to five times and take the median or best — launch technique alone can vary runs by 0.2s or more
• Use the same stretch of tarmac each session; if you suspect a slope, run both directions and average
• Note conditions: cool, dense air helps a combustion engine but cold tyres hurt traction, and EVs are sensitive to battery temperature and state of charge
• Keep the load similar — a full tank weighs 30–40 kg more than a near-empty one, and a passenger more again
• Check tyre pressures; they change both grip off the line and rolling resistance

What do the time and confidence band actually tell you?

Every result gives you two numbers, and both matter. The time itself — say 5.87s — and a ± confidence band that says how much to trust it. A tight band of a few hundredths means the GPS fix was strong and the mount solid; a wide band means signal or mounting was compromised, and the honest move is to bin that run and repeat it.

Be equally honest about what phone timing is: a very good estimate, not a certified timing system. It will not settle a protest at a sanctioned drag meet, but it will absolutely tell you whether that remap bought you three tenths. Runs stay logged on the phone — PitLaunch turns each one into a shareable 9:16 run card with the speed trace — and because everything is processed on-device with no account or analytics, your location and motion data never leave the handset.

Step by step

1. 1

   Mount the iPhone rigidly

   Fix the phone in a firm windscreen or air-vent mount so it cannot rock or rattle — a loose phone corrupts the accelerometer data and widens the confidence band on your result.

2. 2

   Open the app and grant permissions

   On first launch, allow precise location and motion access; the timer fuses GPS speed with the accelerometer, so it needs both. All of it is processed on the phone.

3. 3

   Wait for a solid GPS fix

   Park with a clear view of the sky and give the phone a few seconds to lock on. Avoid tree cover, tall buildings and anything overhead.

4. 4

   Arm the timer before you set off

   Choose your start convention — true standstill or 1-foot rollout — and arm the run while stationary. Launch detection is automatic from here, so there is nothing to press at launch.

5. 5

   Come to a complete stop, then launch hard

   From a genuine standstill, accelerate as hard as grip allows. The app detects the launch itself and starts the clock at the exact instant the car moves.

6. 6

   Drive cleanly through the target speed

   Keep accelerating past 60 mph (or 100 km/h) so the run captures fully; a longer pull also records the ⅛-mile split and quarter-mile with trap speed.

7. 7

   Stop safely and read the result

   Once stationary again, check the time and its ± confidence band. Repeat three to five times and keep the runs with the tightest bands.

Frequently asked questions