Vehicle

1 · Turn on the sensors

The phone’s tilt and rotation sensors do all the measuring — on an iPhone this is the same fused motion data the built-in Measure app uses, the best available to any app. iPhone asks permission once per visit.

2 · Flat check (15 seconds, once per phone)

Teaches the app which way your phone’s sensors point. Lay the phone flat on a table, screen up, tap the button, hold still — then when asked, spin it at least a quarter turn either direction (looking down at the screen) while it stays flat on the table, then tap Done spinning.

2b · Zero against a level (optional, once per phone)

The gauge-zero step below cancels bar and mounting error for camber, but nothing else corrects a phone that simply reads a couple of degrees off even by itself — for example the plumb/level dots on Camber, Caster, and Toe. If you have a trusted digital level, use it here once to zero that out for good.

3 · Zero the gauge

Cancels the small built-in lean of your phone and the gauge bar. Do this once each time you mount the phone in the bar. Hold the bar on any wheel, upright (feet at 12 and 6 o’clock), and follow the three captures.

4 · Measure the floor

The fix for a floor that isn’t level. A sideways slope leans the whole vehicle, which shifts every camber reading. Caster and toe don’t need this — the way they’re measured cancels floor slope out.

What tilts the truck is the height difference between the two tire contact patches — not how the concrete happens to slope at any one spot. So the bar gets walked from tire to tire along the axle line and the rises are added up. On a wavy floor that lands somewhere quite different from one measurement taken wherever the bar happened to fit, and it shows you how wavy the floor is while it does it.

Track = tire centre to tire centre across the axle. Bar length decides how many placements a walk needs.

Measure the rear-axle line too if you’ll be doing rear camber. Re-measure whenever the vehicle gets rolled to a new spot.

Target specs —

Front axle

Rear axle

Toe is total across the axle, positive = toe-in. Specs grade the Results page; edit freely — each vehicle remembers its own numbers.

Session

Bar upright on the wheel lip (feet at 12 and 6), screen facing you. Tap the wheel you’re on first so the live number uses the right side, hold still, capture when the steady light is green. The plumb dot below the readout only watches side-to-side twist — leaning the bar forward/back is the camber reading itself, so plumb won’t (and shouldn’t) react to that; it flags if you’re holding it rotated sideways.

Take three or four readings per wheel, lifting the phone off the bar and re-seating it between each one. Every tap adds a reading rather than replacing the last, and the tile shows the average, how far the readings scattered, and how tight that average is. Holding the phone by hand means each placement sits a little differently — that scatter is the real error here, and one reading can never show it to you. Tapping again without re-seating measures nothing new.

Steering sweep

Caster can’t be read standing still — it shows up as camber change while you steer. The bar stays on one front wheel; the app tracks how far you’ve steered and grabs camber at 0°, +15° and −15° automatically. Floor slope and gauge zero cancel out on their own here.

Sweep each wheel two or three times, re-seating the phone on the bar between sweeps. Caster divides a camber difference by sin(+15°)−sin(−15°) = 0.518, so every bit of hand-held placement scatter comes back magnified about 1.9× — a fifth of a degree of sloppiness lands outside the ±0.5° spec. Sweeps add up like camber readings do, and the tile reports the spread so you can see whether to trust the number.

Bar horizontal across the wheel (feet at 3 and 9 o’clock), top of phone toward the front bumper on every wheel. The gyro carries the pointing angle from wheel to wheel; revisiting the first wheel at the end measures the sensor’s drift so it can be subtracted. Carry the bar smoothly — no flips, no spins. The level dot below the readout stays live through the whole carry, not just at each stop.

All-4 measures front toe, rear toe, and references the fronts to the rear axle — needed for steering-wheel centering.

Frame centerline (optional cross-check)

A truck's frame rails are manufactured straight and parallel to its true centerline — the same reference collision/frame shops use to check for impact damage. Pressing the phone against a straight, undamaged section of each rail and comparing headings gives a second, independent "straight ahead" — separate from the rear axle, useful for catching a subtly bent frame or an offset rear axle before you trust the thrust line completely.

Pick the front and rear frame check-points — usually the flat rail sections just behind the front bumper and just ahead of the rear bumper — because on a Sonoma-style ladder frame those are normally reachable from outside the truck, no jack stands needed. Avoid any kicked-up, notched, or visibly bent section.

No gauge bar needed here — case off, hold the bare phone flat against the rail's outer face, screen up, top of the phone pointing toward the truck's front, same as a wheel capture.

Run + Frame rails mode above. It measures each rail front-to-rear first (a built-in straightness check — a bent rail flags itself before it can mislead you), then reports the frame centerline against the thrust line already captured in the same pass.

Center the steering wheel

The trick: the rear axle defines the direction the vehicle actually travels (the thrust line). The fronts must be set square to that, not to the body. All-4 passes measure each front wheel against the thrust line, so:

• Strap the steering wheel dead center (bungee through the rim to the seat frame) and keep it there for all measuring and adjusting.
• Run 2–3 all-4 passes. Results shows LF and RF toe individually vs the thrust line.
• Adjust each side’s tie rod until LF and RF each read half the total-toe target. Equal halves = wheels square to the thrust line = steering wheel stays centered driving straight.
• If a test drive still shows a cocked wheel: note which way, then move both tie rods the same small amount in the same steering direction (e.g. wheel cocked left → lengthen right rod, shorten left rod equally on a front-steer rack — small steps, re-drive).

Tape toe (trustworthy cross-check)

Mark the middle tread block on each tire of one axle at hub height, front and rear of the tire. Measure across the vehicle: front-of-tire marks, then rear-of-tire marks (roll half a turn if the frame blocks the tape — same marks). Toe-in = rear wider than front.

Mark spacing = front mark to rear mark on one tire (≈ tire diameter if marks are at hub height).

Report card

Past sessions

Build the gauge bar

One straight bar, two bolt feet, rubber straps for the phone. Half an hour, ~$20. One bar fits all three vehicles if you slot the foot holes or drill two sets.

Materials

• Bar: aluminum flat bar or rectangular tube, 1″–2″ wide, 20–24″ long. A cheap 24″ aluminum level works great. Straightness only matters at the two feet, not the middle.
• Feet: two 5/16″ bolts, 1½″ long, each with two nuts (jam-nut). Space them so the bolt tips land on the wheel’s machined rim lip — the ring where clip-on weights go (≈15½″ apart on the Sonoma’s 15s; wider on the Cayenne/Highlander alloys — slot the holes or drill a second set). Never on the tire; rubber bulges.
• Phone mount: two heavy rubber bands or a velcro cinch strap around bar and phone (case off, back flat against the bar). It must not shift between captures.

Why it works even if built sloppy

The two bolt tips define the measuring line — the bar doesn’t have to be perfect, and unequal foot lengths get canceled by the gauge-zero step. Only two things matter: feet on clean metal lip, and the phone strapped so it can’t move.

Install on your iPhone

• There is nothing to download. This web page is the whole app. The download icon in the corner belongs to Claude’s viewer — ignore it.
• For a home-screen icon: open this page in Safari (if it opened inside the Claude app, copy the link into Safari), tap the Share button (square with up arrow) → Add to Home Screen. It opens full screen like a real app.
• Tap Enable motion sensors each time you open it and hit Allow (iPhone rule, one tap per visit). The sensors tag at the top also works as the button.
• Use Keep screen awake in Setup so it doesn’t lock mid-measure; brightness up for sunlight.
• Everything is saved on the phone itself (specs, calibrations, sessions) — it works with no signal in the garage once loaded.

Day-of checklist

• Tires at equal, correct pressure. Normal load in the vehicle.
• Park on the flattest spot you have, wheels straight. Bounce each corner and roll a foot forward to settle.
• Setup tab top-to-bottom: vehicle → sensors → flat check → gauge zero → floor.
• Measure everything before wrenching: camber all 4 → caster sweeps → toe passes.
• Adjust in this order: caster → camber → toe. Toe always last — everything else disturbs it.
• After every adjustment: drop the jack, roll a foot, bounce, re-measure. Never trust a reading taken right off the jack.
• Steering wheel strapped centered for all toe work.

What the floor trick actually does

Camber is judged against gravity, but the spec assumes level ground. If the floor drops ½° toward the passenger side, the whole vehicle leans that way: the gauge reads the passenger wheel ½° more positive and the driver wheel ½° more negative than truth. The floor step measures that lean along the axle line (a flipped pair of captures, so the phone’s own flat error cancels) and the app adds it back with the correct sign per side — separately for the front and rear axle spots.

Caster is immune (computed from camber differences during the sweep — the lean sits in every reading equally). Toe never references gravity at all. Front-to-back slope barely matters for any of the three.

Honest accuracy

Safari feeds motion data at 60 Hz from the same fused sensor stack native apps use; every capture averages ~80 samples. Camber and caster sit comfortably inside spec windows. Gyro toe is the tight one — average 3 passes, then let a tape measurement make the final call.