Slope and wind: how they change your times
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.
Slope
Gravity helps you downhill and fights you uphill. On a 1% grade, gravity adds or removes about 0.01 g — small, but over a 10-second run it is worth a noticeable amount of speed.
Holeshot measures the slope of every run with the iPhone's barometer (and GPS altitude as a fallback) and prints it on the timing card, so a downhill run cannot pass as a personal best without you seeing it.
Wind and air density
A head or tail wind changes aerodynamic drag, which matters most at high speed. Hot, humid air or high altitude reduces engine power in non-turbo cars. The fair comparison is two runs in opposite directions, averaged.
FAQ
What slope is acceptable?
Under about ±1% is generally fine for comparisons. For records, average runs in both directions.
Holeshot: 0-60 & 0-100 Timer
Motion sensors + GPS at 100 Hz. Every split, every run, hands-free.