A smartphone can time a 0–100 km/h in a useful way — if you accept about 0.2 to 0.5 s of uncertainty and avoid canyon streets. OpenRank relies on the device GPS during the trip; it is not a wheel sensor, nor a 20 Hz competition box.
Where the error comes from
- Sample rate — many phones supply ~1 point per second. Between points, speed is interpolated.
- Satellite geometry — open sky is better. Buildings, forest, tunnels = wild spikes.
- Software smoothing — iOS and Android filter jumps. A 0–100 can look “soft” by one or two tenths.
- Cold start — the first seconds after launching indoors are the worst.
When the phone is enough
| Goal | Smartphone | Dedicated GPS / OBD |
|---|---|---|
| Compare summer vs winter tyres | Yes | Overkill |
| See if my GTI lost 1 s | Yes, several runs | Cleaner |
| Publish a record to the tenth | No | Yes |
| Track consumption / pace / history | Yes (OpenRank) | Depends on the tool |
Good practice with OpenRank
- Wait for a GPS fix before you accelerate (icon / speed already coherent at a standstill).
- Phone in the open, not under three layers of carbon in the boot.
- Same road, same direction, to compare two sessions.
- Ignore an isolated 180 km/h spike between two buildings: that is noise.
The run protocol is in how to measure 0–100 km/h accurately.