How to Time 0–100 km/h or 0–60 mph with Your iPhone (and How Accurate It Is)

The problem

You want to know how quick a car really is, and comparing it with the claim in a brochure needs timing gear. The usual phone solutions count whole GPS samples, so an eight-second run is wrong by half a second either way.

Steps (Pro)

1. Open Acceleration.
2. Choose your speed unit so the target is right.
3. Arm a run. If you’re still moving, the app waits until you’ve come to a complete stop.
4. Launch. The clock starts the moment you move and stops when you cross the target.
5. Review the time and splits; every run is kept so you can compare.

How it measures

GPS reports about once a second. Instead of taking the first sample at or above the target, SpeedTrace interpolates the moment the speed crossed it between the samples either side, and does the same for the launch. That cuts the error from about ±0.5 s to roughly ±0.15 s. It is honest about the remaining uncertainty on screen.

Do it safely and legally

Use a closed course or private property. Never test on public roads: it’s dangerous and illegal in many places.

Tips

• Wait for GPS Good, and start from a standstill with the phone mounted.
• Do the run both ways on a flat road to cancel wind and slope.
• Compare your own runs with each other; don’t compare to a different device.

FAQ

How accurate is it? Better than counting whole GPS samples, but not a timing beam. Interpolation brings it to around a tenth of a second or two; the app says so on screen.

Which targets are used? 0–100 km/h if your unit is km/h and 0–60 mph if mph, with intermediate marks.

Is it free? No. 0–100 timing is part of SpeedTrace Pro.

Where should I do it? On a closed course or private land, never on public roads.