Why phone 0-60 and 0-100 apps are seconds off
Phone GPS reports about once a second and late. Here is exactly why GPS-only timers read slow, start late, and miss splits — and how motion-sensor fusion fixes it.
The short answer
An iPhone's GPS delivers a position and speed roughly once per second, and the speed it reports describes the car a fraction of a second ago. A timer that relies on GPS alone starts the clock late (it needs to see movement first) and reads each split off data that is already stale.
At 100 km/h a car covers about 28 metres every second, and a quick car is gaining several km/h in that second. One second between readings, plus a delay of a few tenths, is enough to put a 0-100 time off by anywhere from a tenth to several seconds. That is the complaint in almost every low-rated review of GPS timer apps: "it said 6.3 s, my car does 3.3".
Where the error comes from
Sampling: at 1 Hz, the moment you actually crossed 100 km/h falls somewhere between two readings. The app has to guess.
Latency: the reported speed lags the real speed. During hard acceleration a lag of half a second can mean 10 km/h or more of difference.
Start detection: GPS speed near zero is noisy, so apps wait for a clear reading before starting the clock — by then you have been moving for a while.
Smoothing: the GPS chip filters its own output, which rounds off exactly the sharp change a launch produces.
How Holeshot does it differently
Holeshot reads the iPhone's motion sensors 100 times a second. The accelerometer sees the launch the instant the car moves, so the clock starts on the real launch, not on the first GPS fix that notices it.
The speed curve comes from integrating that acceleration, which is smooth and immediate. GPS is then used for what it is good at — long-term truth — to remove the accelerometer's slow drift. After the run, the whole curve is fitted against every GPS fix, including an estimate of this phone's own GPS delay, which Holeshot learns over time.
In our test suite of 300 simulated runs with realistic phone-sensor faults (GPS delay, smoothing, dropouts, vibration, a tilted mount), Holeshot's 0-100 km/h times landed within 0.09 s of the true value 95% of the time. A GPS-only timer on the same data was off by about 0.6 s on a typical run, and by more than 2 s on one run in twenty. These are simulation results; real-world accuracy also depends on mounting and sky view.
Getting the best accuracy
Mount the phone firmly — any angle works, but it must not move during the run.
Give it a clear view of the sky; avoid tunnels, tall buildings and heavy tree cover.
Stop completely and wait for the tree to go green before you launch.
Run in both directions on the same stretch and average, to cancel out slope and wind.
FAQ
Are phone 0-60 apps accurate?
Apps that rely on GPS alone usually are not: 1 Hz GPS with a few tenths of delay can put a 0-60 time off by tenths to seconds. Apps that fuse the 100 Hz motion sensors with GPS, like Holeshot, are far more accurate.
Do I need an external GPS box?
A dedicated 10 Hz GNSS logger is still the reference for professional data. Holeshot is designed to get as close as a phone can without one, using sensor fusion instead of extra hardware.
Holeshot: 0-60 & 0-100 Timer
Motion sensors + GPS at 100 Hz. Every split, every run, hands-free.