The bracket

The Rim Reader bracket in graphite, with a phone clamped in it by an orange wedge — Print the wedge in a different colour from the bracket, so a missing wedge is obvious.

Our bracket Print files at launch

The Rim Reader bracket is the design the app is built around. It prints on a home 3D printer with a 220 × 220 mm bed, needs nothing bought, and fits phones 67 to 91 mm wide in their case with a set of slide-in wedges.

The print files will be published when the app launches. What’s coming.

Before every use

Check the bracket for cracks, looseness or wear, and don’t use it if you find any. Keep the prong noses clean and undamaged: they are the measuring surface. A bracket is printed by you or by others, so its quality is in your hands.

The parts

One bracket, one wedge

The bracket is a solid 15 mm slab with a tray for the phone. A fixed rail runs along one long side; the phone’s right side bears on it. An end stop at the FRONT end holds the phone’s top. The other long side is a tapered wall, angled 4.5°. A window in the rail leaves room for buttons on the phone’s right side, and a channel under the phone’s top end leaves room for the camera bump.

Four prongs, one at each corner, are the only parts that touch the wheel. Each has a rounded nose, so it makes the same line contact on the rim’s lip every time. Only the two on the wheel side touch; the other pair lets either long edge face the wheel.

The wedge is a tapered key. It drops into the gap on the phone’s left side, and pushing it toward FRONT clamps the phone against the rail and the end stop. At 4.5° it locks itself: it stays put until you pull its tab.

The empty bracket from above at an angle, showing the tray, the rail with its window, the end stop with FRONT engraved, the camera channel and the four prongs, with an orange wedge beside it — The bracket and a long wedge. The window in the near rail is for the phone’s right-side buttons; the slot across the tray is the camera channel.

The bracket, wedge and phone pulled apart, showing the tray, rail, end stop, camera channel and the four prongs — Bracket, wedge and phone, pulled apart.

Sizes

Bracket: 210 × 120 × 15 mm slab; 210 × 184 mm across the prongs; walls 17 mm above the floor of the tray
Prongs: Four, 196 mm apart on each long edge; reach 32 mm past the edge to clear the tire’s sidewall; 14 mm wide, 8 mm tall, rounded 7 mm nose
Phones: 67 to 91 mm wide in their case; up to 15 mm thick including case and camera bump; the tray is 172 mm long, and longer phones may overhang the open end
Wedges: Two sets of eight: long (140 mm) for phones with no buttons on the left side; short (40 mm) for phones with buttons there. Each wedge covers 3 mm of phone width.
Markings: FRONT with an arrow either side, engraved on the front end; the wedge’s width band engraved on its top
Material: PETG, about 225 to 345 g for the bracket and one wedge
Design: Version 1.7.0

Which wedge

Find your wedge

Measure the phone in its case, at its widest point. Lay a ruler across it with the case on.
Check the left side. Hold the phone screen toward you, top up. Buttons on the left side take a short wedge; no buttons there, a long one.
Print the wedge marked with your band. An 83 mm phone takes the 82-85 wedge.

On a boundary, such as 82.0 mm, either neighbour fits; for a short wedge take the narrower band. If a short wedge presses a button, use the next band down.

All sixteen wedges in two rows: eight long wedges and eight short ones, each a size thinner than the last — The long set (behind) and the short set (in front), eight sizes each. You print only the one that fits your phone.

Choose Your Wedge

Popular phones and their wedge

A guide only. The cased widths are estimates: the phone’s published width plus 6.5 mm for a typical case, except the Pixel 8 Pro, which we measured. A slim case can be 2 to 4 mm narrower and drop a phone one band, so measure your own.

The app runs on Android today; iPhones are listed for the bracket only, ahead of the iPhone version. Check your own phone’s left side before choosing the set. Phone names are their makers’ trademarks, used only to identify the phones.
Phone	Width, bare	In a case (est.)	Wedge	Set
Google Pixel 8 Pro	76.5 mm	83 mm (measured)	82-85	long
Google Pixel 8	70.8 mm	77.3 mm	76-79	long
Google Pixel 9	72.0 mm	78.5 mm	76-79	long
Google Pixel 9 Pro XL	76.6 mm	83.1 mm	82-85	long
Google Pixel 9a	73.3 mm	79.8 mm	79-82	long
Google Pixel 10a	73.0 mm	79.5 mm	79-82	long
Google Pixel 7a	72.9 mm	79.4 mm	79-82	long
Samsung Galaxy S24	70.6 mm	77.1 mm	76-79	long
Samsung Galaxy S24 Ultra	79.0 mm	85.5 mm	85-88	long
Samsung Galaxy S25	70.5 mm	77.0 mm	76-79	long
Samsung Galaxy S25+	75.8 mm	82.3 mm	82-85	long
Samsung Galaxy S25 Ultra	77.6 mm	84.1 mm	82-85	long
Samsung Galaxy A16 5G	77.9 mm	84.4 mm	82-85	long
Samsung Galaxy A36 5G	78.2 mm	84.7 mm	82-85	long
Motorola moto g power (2025)	77.1 mm	83.6 mm	82-85	long
Motorola moto g stylus (2025)	74.8 mm	81.3 mm	79-82	long
Motorola edge (2025)	73.1 mm	79.6 mm	79-82	short
OnePlus 13	76.5 mm	83.0 mm	82-85	short
Nothing Phone (3)	75.6 mm	82.1 mm	82-85	short
Apple iPhone 15 / 16 / 16e	71.5–71.6 mm	78.0–78.1 mm	76-79	short
Apple iPhone 16 Pro / 17 / 17 Pro	71.5–71.9 mm	78.0–78.4 mm	76-79	short
Apple iPhone 16 Pro Max	77.6 mm	84.1 mm	82-85	short
Apple iPhone 17 Pro Max	78.0 mm	84.5 mm	82-85	short
Apple iPhone Air	74.7 mm	81.2 mm	79-82	short

Not designed for

Phones narrower than 67 mm or wider than 91 mm in their case (the bare “mini” phones are too narrow).
Phones shorter than about 140 mm in their case: they get too little bearing on the rail.
Book-style foldables, and phones with buttons on the top edge, which faces the end stop.
Very thick rugged cases that take the phone past 15 mm.

A phone whose camera bump starts at its top edge rests the bump on the ledge at the end stop and sits slightly nose-up. That is normal: Bracket Calibration measures it and corrects for it.

Fitting the phone

Designed to go in or out in ten seconds

Phone in, screen up, top against FRONT. Slide it forward until its top touches the end stop and its right side touches the rail.
Drop the wedge in, thin end first. It goes in the gap on the phone’s left side, thin end toward FRONT.
Press the phone down. Push the wedge. One finger holds the phone flat while another pushes the wedge’s tab toward FRONT until it stops. Push it again once the bracket has reached the outdoor temperature.

To release, pull the tab and lift the phone out. A wider phone ends up with the wedge further back; that is normal.

Then run Bracket Calibration. If the phone can move in the bracket, every reading will be wrong, and the calibration will say so.

Phone in the Bracket

Printing

Print settings

Material: PETG for every part
Nozzle and layers: 0.4 mm nozzle, 0.2 mm layers (it also prints on a 0.6 mm nozzle with 0.3 mm layers)
Bracket: Back face down, as the file comes. 4 perimeters, 8 top and 8 bottom layers, 30 to 40 % gyroid infill
Wedge: Standing as the file comes, 100 % infill: it carries the clamping load
Supports: None, anywhere
Bed: 220 × 220 mm or larger; the bracket and a wedge fit on one bed
Brim: None on a textured PEI sheet; use one on a smooth or cold bed

Optional: 0.12 mm layers for the first 10 mm of the bracket give smoother prong noses. A large flat PETG slab can lift at the corners on an open printer; a brim and an enclosure help.

Materials and care

Print it in PETG

PLA and a hot car don’t mixPLA softens at about 55 °C. A PLA bracket left in a hot car can take a set with no sign you can see, and every reading after that is off. Use PLA only for a bracket that never leaves the house.

Two colours. Print the wedge in a different colour from the bracket, so a missing wedge is obvious.
After a drop, a reprint, or a new phone: run Bracket Calibration again. Otherwise every 30 days; the app reminds you.
Keep the prong noses clean. Wipe the rim’s lip where they sit, and keep them off the tire’s rubber.
Temperature. The bracket is meant for 5 to 50 °C. Push the wedge again once it has reached the outdoor temperature.
Before the car moves, take the phone and the bracket off the wheel.

Camera version

A bracket with a window

A second version of the bracket has the camera channel cut right through, so the phone can scan the VIN or the tire label without coming out of the bracket. It is about 30 g lighter.

Use the standard bracket for measuring.

The camera version of the bracket, with a window through the slab under the phone's top end — The camera version, with its window under the phone’s camera.

Make your own

Seven things a bracket needs

Rim Reader works with a bracket you make yourself if it does these seven things. Then run Bracket Calibration with your phone in it.

Two straight edges, two prongs each. Each long edge has two prongs that rest on the rim’s lip. Ours are 196 mm apart. Prongs closer together work, but dirt under one costs more.
Prongs that reach past the tire. The prongs stick out about 32 mm past the edge, so they reach the lip without touching the tire.
Phone flat, long side along the prongs. The phone lies flat, screen up, its long side along the line between the prongs and its top toward FRONT.
Phone held tight, bracket stiff. The phone is pushed into a corner and clamped, so it cannot shift or rock. Pressing on the far edge should not tilt the phone; ours is a solid 15 mm slab.
Flat back, steady on its end. It lies still on the floor, and stands steady on its end against a wall. The calibration and the floor readings need both.
A FRONT mark. FRONT points to the front of the car at every wheel. The edge on the phone’s right side is the rail edge; camber is read on it.
Run Bracket Calibration. It measures your bracket’s own small differences and refuses a phone that moves. Run it again for a new phone or a new bracket.

The ideas behind it

The rim’s lip is the reference. Its flat outer ring is square to the axle, so two contacts anywhere on it give a line parallel to the wheel.
Hard stops locate; the clamp only holds. A rigid rail, end stop and floor position the phone. Springy phone holders are too soft to hold an angle.
Contact on the prongs only, never the tire or the hub.
Calibrate, don’t machine. Any fixed difference either cancels between the two wheels of an axle or is measured once by the app and subtracted.

A printed bracket that holds your phone true

Our bracket Print files at launch

Before every use

One bracket, one wedge

Sizes

Find your wedge

Popular phones and their wedge

Not designed for

Designed to go in or out in ten seconds

Print settings

Print it in PETG

A bracket with a window

Seven things a bracket needs

The ideas behind it