Standalone: record laps with just your phone

GPS1 per second

The LapSnap Standalone record screen with GPS acquired, motion sensors active and a Go button

Motion sensors25 per second

LapSnap Standalone turns your phone into a lap timer. It records a track session with just your iPhone or Android phone, with no other hardware. It times your laps live at the start/finish line, and when you stop it turns the recording into a session with lap times, a track map and lap comparisons.

Google Play

App Store

Record a session with your phone

  1. Mount the phone securely, high on the vehicle, where it has a clear view of the sky.
  2. Turn off your phone's automatic crash calls (see the questions below).
  3. Open LapSnap, tap the plus button and choose Record.
  4. Allow precise location, then wait for GPS to connect. LapSnap finds the nearest track on its own, or you can pick one.
  5. Tap Go and drive. LapSnap shows your current lap, your previous lap and the gap to your best.
  6. Tap Stop when you finish.

How a phone keeps up with a lap timer

A dedicated GPS lap timer takes 10 to 25 position fixes a second. A phone takes about one. At 100 mph that is a fix every 45 meters, so joining the dots cuts every corner and can miss the exact moment you cross the line.

A corner with five GPS fixes one second apart. Straight lines between them cut the corner; LapSnap's path follows the curve. GPS fix, one per second Joining the fixes cuts the corner LapSnap's path, filled in from motion sensors
Illustration of one corner taken at about 100 mph.

LapSnap fills the gaps with your phone's motion sensors. Between GPS fixes it estimates where you are from how the phone is moving, a technique called dead reckoning. It weighs each fix by the accuracy the phone reports, so a single bad fix does not throw the path off.

When you tap Stop, LapSnap processes the whole session again with every fix and sensor reading in view, before and after each moment. It holds the path to the track's racing surface, then times each crossing of the start/finish line between fixes instead of at the nearest one.

Two seconds of recording: three GPS fixes one second apart, motion sensor samples in between, and a start/finish crossing timed at 1.38 seconds, between two fixes. Motion sensor samples, about 20 a second Line crossed at 1.38 s GPS fix, 0 s GPS fix, 1 s GPS fix, 2 s
LapSnap times the line crossing between GPS fixes.

How accurate is it?

We tested phones on track against a dedicated GPS lap timer on the same vehicle. With the phone mounted where it had a clear view of the sky, laps came within about a tenth of a second of the lap timer.

Difference from the dedicated lap timer, in seconds. Phones taped to the tail of a motorcycle, two test sessions.
LapAndroid phoneiPhone
1+0.03-0.12
2+0.02+0.01
3-0.050.00
4-0.01

Where you put the phone matters more than which phone you use. Your body blocks GPS signal, so a phone in a pocket or strapped to your leg sees far less of the sky than one on the vehicle.

Median position error by phone placement: arm 4.4 meters, mount 6.0 meters, leg 20 meters. Arm 4.4 m Mount 6.0 m Leg 20 m
Median distance between the phone's GPS position and the lap timer's in one test session. Shorter is better.

Get the most accurate laps

  • Mount the phone high. The dash, behind the windscreen or the tail of a bike all work. Avoid pockets and leg straps.
  • Wait for GPS. Tap Go only once LapSnap shows GPS connected and has found your track.
  • Turn off battery saving. Low Power Mode can dim the screen, and some Android phones stop GPS in the background to save battery. Exclude LapSnap from battery optimization.
  • Watch for Weak GPS. LapSnap marks sessions that had a poor signal. If you see it, move the phone to where it has a clearer view of the sky.

Standalone is in beta. Tell us how it works for you at support@lapsnap.app.

Questions

Yes. LapSnap Standalone, added in version 2.6.0, records sessions with just your iPhone or Android phone. Tap the plus button, choose Record, wait for GPS and tap Go.

With the phone mounted where it has a clear view of the sky, our test laps came within about a tenth of a second of a dedicated GPS lap timer. A phone in a pocket or on your leg loses GPS signal and times laps far less accurately.

Mount it securely, high on the vehicle, where it can see the sky: on the dash, behind the windscreen or on the tail of a bike. Never handle the phone on track.

Hard braking and impacts on track can trigger your phone's crash detection and call emergency services. Turn it off before you drive: on iPhone in Settings > Emergency SOS > Call After Severe Crash, and on Android in Personal Safety app > Features > Car crash detection.

The phone had a poor GPS signal for part of the session, so its data may be less accurate. Next time, move the phone to where it has a clear view of the sky.

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