Acceleration and braking tests

Measuring a launch, braking time and braking distance, and comparing the results over time.

The Acceleration screen times launches and braking from the speed read off the car. It has three tabs: Acceleration, Braking and Brake Dist.. The quarter mile sits inside Acceleration, as a measurement from 0 to 402 meters.

Only run these tests somewhere private, closed to traffic and free of obstacles.

  1. Create a test

    Tap Add. In Choose test type, select what will be measured. The tab you are on sets the test family, and inside it you choose the ranges, such as 0 to 100 or the quarter mile.

  2. Let the app calibrate

    With the car fully stopped, the app calibrates the phone's orientation and shows Calibrating orientation. That calibration is what lets it tell forward acceleration apart from lateral acceleration.

    If the car moves during the process the calibration fails and the app asks you to repeat it.

  3. Take the measurement

    Tap Start Test. The first time, the Ready to start screen sums the procedure up: keep the car fully stopped, accelerate and the timer of each range starts and stops on its own; on braking tests, reach the starting speed and brake firmly. Confirm with Got it.

    The timer of each range fires automatically as the speed rises, with no tap needed during the launch. Stop Test ends the measurement at any point.

  4. Read the result

    Tap a measurement in the list to open the Test details. Besides the time, the screen shows the Peak acceleration, the Peak lateral and the chart of the launch.

    A measurement with the GPS tag was taken without an adapter and is less precise.

  5. Follow braking over the months

    The Braking and Brake Dist. tabs are the most useful ones in everyday use. Repeat the measurement on the same stretch, from the same starting speed, once a month.

    A braking distance that grows over time can point to pad or tire wear, and the number changes before the difference can be felt through the pedal.

If something goes wrong

The calibration needs the car fully stopped. An idling engine usually does not get in the way, but a slope or slow movement prevents the reading. Stop on level ground, with the brake on, and try again.

Rest the phone in a firm mount rather than leaving it loose on the seat. On cars with more vibration, raise the Accelerometer calibration tolerance to High, in Navigation.

Without the adapter the test uses GPS speed, which updates less often and can produce imprecise times. The app lets you carry on, but marks the measurement with the GPS tag.

For a reliable measurement, connect the adapter before starting.

The pause is deliberate. During the test, the export to Home Assistant, MQTT and the driving events are suspended for a moment, so that the adapter's whole capacity is dedicated to reading speed. Everything returns to normal at the end of the measurement.

Only compare measurements taken under the same conditions: same stretch, same gradient, same engine temperature and same fuel level. A slight downhill cuts the time without anything having changed on the car.

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