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.
A step-by-step guide to timing your car's acceleration with an iPhone: mounting, staging, launching, and reading the result — safely, on a closed course.
Rollout is the first foot of movement that drag strip timers and US car magazines leave out. It typically makes a 0-60 mph time 0.2–0.3 s quicker.
Pre-stage, stage, three ambers, green and red: how the drag strip starting lights work, the difference between a Sportsman and a Pro tree, and what a red light means.
In drag racing, the holeshot is winning off the start line: reacting and launching better than the other lane, even with a slower car.
The 60-ft time measures the first 60 feet of a drag run. It is the clearest read on your launch, and every tenth there is worth more than a tenth at the finish.
Trap speed is how fast you are going at the end of the run. ET reflects launch and traction; trap speed reflects power-to-weight.
Why 100-200 km/h is the favourite benchmark for high-performance cars, what good times look like, and how it is measured.
Roll racing starts from a cruise instead of a standstill. Here is how 60-130 mph, 40-70 mph and 80-120 km/h intervals are timed.
A 1% downhill grade can flatter a 0-100 by a tenth or more. Holeshot uses the iPhone's barometer to measure the slope of every run.
1/4 mile is 402 m (1,320 ft); 1/8 mile is 201 m (660 ft). How the two relate and why many tracks now run the eighth.
Dedicated 10 Hz GNSS performance meters are the reference. Here is what they do differently, and how a phone app can close the gap with sensor fusion.