About Rim Reader
What is Rim Reader?
A do-it-yourself measuring aid. It estimates your wheel alignment angles from your phone’s sensors and a 3D-printed bracket held against each wheel. It is not professional alignment equipment, and it tells you to have a qualified shop check the alignment before highway driving.
What does it measure?
Toe for each wheel and each axle’s total, steer-ahead (whether your steering wheel will sit straight), thrust angle (optional, read at the front doors) and camber (optional, with floor correction). It also tells you which way to turn each front tire. How it works.
Does it measure caster?
Not yet. Caster is planned, read by steering each front wheel left and right. It is greyed out in the app until it is built and tested.
Does it use the phone’s compass?
No, never. A compass is useless next to a steel car. It uses the gyroscope, which measures turning, and the accelerometer, which measures which way is down.
Who is it for?
Do-it-yourselfers, enthusiasts who align often, mobile mechanics, and shops without an alignment rack. You must be 18 or older to use it.
Should I still go to a shop?
Yes, for anything that matters. Have a qualified shop check the alignment before highway driving or carrying heavy loads, and after suspension or steering work. Rim Reader is for checking and adjusting in between.
Can I use it on someone else’s car?
Yes, but you are responsible to its owner, and you must tell them the results are estimates.
Getting it
When can I get it?
Rim Reader is in testing on Android and is coming soon to Google Play. Email info@rimreader.com to hear when it’s out.
How much will it cost?
Pricing will be announced at launch.
Is there an iPhone version?
Not yet. Android comes first, and an iPhone version will follow. It has to pass the same tests first.
Which phones work?
Android 10 or newer, with a hardware gyroscope. Bracket Calibration grades each phone’s gyroscope Good, Marginal or Not suitable, and a weaker grade lowers the confidence of its results.
Do I need an account or internet?
No account and no login. Measuring works fully offline. The internet is used only, and only if you choose, for the VIN model lookup and for Send Feedback.
Does it know my car’s factory specs?
Not yet. Scanning the VIN fills in the year, make and model, but factory alignment specs are licensed data that costs thousands of dollars a year. We’ll add them once we know the app has found its users. For now, enter the specs from your vehicle’s service information or a shop printout, or use the generic targets, which the app always marks as generic. More on why.
The bracket
Where do I get the bracket?
You print it. Our print files will be published when the app launches. You can also make your own, if it meets seven rules, and run Bracket Calibration with it.
I don’t have a 3D printer.
Many libraries, schools and makerspaces have one, and online print services will print a file for you. Ask for PETG. We may offer ready-printed brackets later.
What should I print it in?
PETG. PLA softens at about 55 °C, so a PLA bracket left in a hot car can warp without any sign you can see. Use PLA only for a bracket that never leaves the house. Print settings.
Can I leave my phone case on?
Yes. Measure the phone in its case to choose the wedge. Very thick rugged cases that take the phone past 15 mm won’t fit.
Will my phone fit?
Phones 67 to 91 mm wide in their case and up to 15 mm thick, at least about 140 mm long. Book-style foldables and phones with buttons on the top edge aren’t designed for. Try the wedge finder.
Does it work with a homemade bracket?
Yes, if it meets the seven rules and you run Bracket Calibration with it. The prongs don’t have to be 196 mm apart.
What is the camera version of the bracket?
The same bracket with a window under the phone’s camera, so it can scan the VIN without coming out. Use the standard bracket for measuring.
Calibration
Why do I need to calibrate?
No printed bracket is perfect and no phone sits perfectly square. Calibration measures the angle between your bracket’s two edges, how the phone sits in it, and the camber zero, and grades your phone. Without it, the app won’t measure.
How often?
Every 30 days, and with a new phone or bracket, or after a drop or damage. The app reminds you at 30 days.
What do I need for calibration?
A hard, flat floor beside a wall or bookshelf, a strip of tape, and a pen to draw a V. It takes a few minutes. Step by step.
Measuring
How long does it take?
About four minutes for a toe lap; a practised user does it in about two and a quarter, and the front axle alone in under a minute. Camber adds a few minutes, on a second trip round the car.
Do I need to jack up the car, or turn plates?
No. The car stays on its wheels on level ground. Don’t jack it up to measure.
Do I tap a button for each reading?
No. Hold the bracket level and still, and the reading is taken by itself. The phone beeps and buzzes, so you don’t need to watch the screen. Turn up the media volume.
Why does the bracket sit on the ground first?
That ten-second rest gives the gyroscope its zero, and it is the only moment the app learns which way is down.
Why does it ask for the same wheel twice in a row?
The second reading, after you lift the bracket off and put it back, measures how well you placed it. Then the app can tell placement error from drift.
Why does it measure the rear wheels too?
The rear axle sets the direction the car actually travels. Each front wheel’s own toe, and whether the steering wheel sits straight, can only be worked out against that line.
Can I measure only the front?
Yes, but one axle alone gives only its total toe. Tick Rear too to get each front wheel’s toe and steer-ahead.
Do I turn the bracket round on the other side of the car?
No. FRONT always points to the front of the car, at every wheel.
Why the door windows?
For the thrust angle, the app needs the body’s direction. The glass is smooth, every car has front doors, and reading the same back corner on both sides makes the curve of the glass cancel out.
Why let the phone sit outside first?
A phone that is warming up or cooling down drifts, and the lap may not close. Give it 3 to 5 minutes in the air you’re measuring in, with the app open.
My lap won’t close. What now?
The app re-reads only the axle that failed, up to twice. After that it ends as Not Closed. Check the phone is locked in its corner, keep the screen on, keep the walks short, let the phone’s temperature settle, and start over. Troubleshooting.
Why did it say Phone Moved?
The second reading at a wheel disagreed with the first. Either the bracket didn’t go back on the same spot, or the phone shifted in the bracket. Push the phone into its corner, lock the wedge, and place it again.
What if the screen turns off or a call comes in mid-lap?
The phone stops reading its sensors, and a walk with a gap is refused. The app keeps the screen on during a lap; keep the app in front.
Does it work on any wheel?
It needs a flat ring on the rim’s lip for the prongs, clear of the valve stem and clip-on weights, with wheel covers off. Generic targets are for cars and light trucks; vehicles over 10,000 lb should use the maker’s specs.
Do my tires need to be at a set pressure?
Set them as you normally run them, as you would before any alignment.
Results
How accurate is it?
In our tests, the typical lap-to-lap variation in total toe was 0.013° (rear) and 0.026° (front), and in camber 0.018°. That is repeatability, not accuracy. It has not yet been compared with a professional alignment rack; that is the next test, and we’ll publish the results. Accuracy.
How does it know a reading is bad?
Every wheel is read twice in a row, which checks your placement, and visited twice, which measures drift. The app removes the measured drift and rates every result High, Medium or Low with plain-language reasons. If the measurement doesn’t close, it shows no numbers rather than wrong ones.
What does Low confidence mean?
A Low result is not necessarily wrong, but it is not evidence. Fix the reasons it lists and measure again before adjusting.
What is steer-ahead?
The front wheels’ average direction compared with the thrust line. If it isn’t near zero, the steering wheel sits turned when you drive straight. It is the commonest reason a car comes back from an alignment with the steering wheel still crooked.
Can I see toe in mm or inches?
Yes, per vehicle: degrees, degrees and minutes, mm or inches. Millimetres and inches need the tire size. Camber and thrust are always in degrees.
Can I compare before and after?
Yes. In History tick two runs and tap Compare. Changes too small to be real show as no measurable change.
Can I print a report?
Yes: a three-page PDF Alignment Report, saved to your phone’s Download/Rim Reader folder. Reports and sharing.
Is there a version for mobile mechanics and shops?
Shop features are built: your name and logo on reports, customer and plate details, before-and-after reports and check-only reports with a recommended service. They are coming with the shop plans.
Privacy and the app
Where is my data kept?
On your phone. Your readings and vehicles aren’t uploaded, and they leave only if you share them (what else leaves the phone). PDF reports are saved in your phone’s Download/Rim Reader folder, where they stay until you delete them. Privacy policy.
What leaves my phone?
Only if you use them: part of the VIN (the first 11 characters with the 9th hidden, plus the model year) for the model lookup; Google’s on-device scanner’s diagnostic information, but never the picture or what it read; and what you send with Send Feedback.
What permissions does it need?
The camera, and only when you open a scanner. No microphone, location, contacts or storage permission.
Is there a tutorial?
Sixteen short animated lessons, which play by themselves before each calibration and each lap while the tutorial is on. Turn it off and on in Settings → Help. Watch them here.
Is it accessible?
The measuring screens work with text up to 200 % and with a screen reader, colour always comes with words, lessons respect the phone’s Remove animations setting, and every reading has a sound and a vibration.
Is there a dark mode?
Yes: Settings → Appearance, with System Default, Light and Dark. Distance switches between miles and kilometres.
How do I report a problem or send an idea?
In the app, Settings → Send Feedback; it works later if you’re offline. Or email info@rimreader.com. Contact and support.