Accuracy
The numbers from our own tests, and what makes the difference between a good reading and a poor one.
Full laps in a row on a car that was not moved, touched or steered between laps. The figures are the typical lap-to-lap variation. Each front wheel’s own toe varied 0.037° (front left) and 0.028° (front right), and both axles were within the app’s own pass mark of 0.05°.
On a second car on a different day, front total toe measured four different ways (toe with camber and thrust, toe with thrust, toe only, and the front axle alone) stayed within 0.034°. The front-only lap took 49 seconds.
| Hold | Rear total toe | Front total toe | Steer-ahead |
|---|---|---|---|
| One hand | 0.069° | 0.038° | 0.089° |
| Two hands | 0.008° | 0.024° | 0.034° |
Letting the prongs touch the tire’s rubber roughly doubled the lift-and-replace error in our tests (0.017° against 0.009°). Slide in only until the prong noses meet the lip.
Lifting the bracket off a wheel and setting it back moved the reading by typically about 0.022°. That is about 0.08 mm of difference across the 196 mm between the prongs, which is why the app reads every wheel twice.
Reading the top of the rim as a reference made camber about 3.5 times more repeatable than gravity alone, which is how a simple digital angle gauge reads it. Four wheels with the floor correction took 2½ minutes.
Choose the floor well. Grit and where the bracket sits change the floor readings, so choose the smoothest, flattest floor you can and wipe it.
Walking round a room and back to the same spot, the phone’s heading came back within 0.001°, 0.009° and 0.039° on three walks. A phone that is still warming up or cooling down drifts more, so let it settle to the outdoor temperature for 3 to 5 minutes before a lap.
The app uses about 2 % of the battery per 15 minutes of measuring, and opens in about a quarter of a second in our tests.
The app shows angles to 0.01°. That is the display, not a claim of 0.01° accuracy: it is finer than the repeatability above. The confidence rating, High, Medium or Low with its reasons, is the better guide to how much a result can be trusted. “A Low result is not necessarily wrong, but it is not evidence.”
Next, cars will be measured right before or after a professional alignment rack to compare toe, thrust and camber, and the results will be published here. Until then, treat readings as estimates, and have a qualified shop check the alignment before highway driving or carrying heavy loads. What’s coming.