In short. A wheel can touch the brakes in three places: the inside of the barrel (the top of the caliper), the back of the spokes (the outer face of the caliper) and the centre (the disc bell and anything bolted near the hub). Wheel diameter is only a first filter. Two wheels of the same diameter and offset can clear a caliper or not, depending on how thick the barrel is and how the spokes are shaped behind the face. The reliable check is the brake maker's profile drawing or 1:1 template against the actual wheel, turned through a full revolution. The gap to leave is the brake maker's figure for that kit, not a rule of thumb from a forum. And two serious sources disagree on spacers as a cure: one brake maker rules them out.
Where can a wheel touch the brake?
| Zone | What touches what | What makes it vary | How it is checked |
|---|---|---|---|
| Inner barrel | The top (outer radius) of the caliper against the inside of the rim | Wheel diameter, barrel thickness, the shape of the drop centre, balance weights stuck inside the barrel | Template or profile drawing against the barrel, all the way round |
| Back of the spokes | The outer face of the caliper against the spokes | Offset, how far the spokes stand behind the mounting face, how they curve towards the rim | Template laid across the back of the spokes, every spoke position |
| Centre | The disc bell and hub hardware against the wheel's centre and mounting pad | Bell height, the depth of the wheel's centre pocket, bolt heads | Template profile at the hub; a trial fit |
AP Racing, which makes brakes for road and race cars, says it is usually the inner spoke area that fouls the outer face of the caliper (AP Racing). That is the zone a diameter figure says nothing about.
Why is wheel diameter not enough?
Because the caliper does not care about the diameter written on the wheel; it cares about the space inside it. Race Technologies, Brembo's official partner, lists the variables that affect clearance as wheel diameter, wheel offset and wheel design (Race Technologies). In practice:
- Barrel thickness. A 19 inch wheel is 19 inches at the tyre seat. The inside of the barrel, where the caliper turns, is smaller by the thickness of the rim wall, and that thickness changes from one wheel and one construction to another. How forged, cast and flow-formed wheels differ is in forged vs cast vs flow-formed.
- Spoke shape. Two wheels with the same offset have their mounting face in the same place, but the backs of their spokes can be at very different distances from the caliper. A wheel whose spokes dish inwards towards the rim, as many concave designs do, can bring the spoke closer to the caliper as it goes outwards: see deep dish and concave wheels.
- Offset. A change of offset moves the whole wheel, spokes included, in or out relative to the hub, and so relative to the caliper. Wheel offset explained gives the arithmetic, and the wheel offset calculator shows the change in millimetres between two wheels.
How do I check before buying?
The brake makers' own method, step by step:
- Get the profile for your exact brake. AP Racing publishes caliper profile drawings in each kit's application guide, and says a full-size drawing can in many cases be sent by post if one is not online. Race Technologies publishes a wheel clearance PDF for each Brembo GT and GT-R system.
- Print it at full scale. Race Technologies insists on 1:1 (100 per cent) printing and puts a ruler on the page to check it. A template printed at 97 per cent by a "fit to page" setting is worse than none.
- Cut out the caliper, the bell and the disc, and stiffen the paper with card if it is flimsy.
- Take a wheel off and lay it face down. Raise the car and support it on axle stands, never on the jack alone, before a wheel comes off; when it goes back on, tighten the wheel nuts or bolts to the car maker's torque figure. Offer the template to the inside: across the back of the spokes and against the barrel.
- Turn it through a full revolution. Spokes are not all the same distance from the caliper at every point, and the gap that counts is the smallest one.
- Compare with the brake maker's minimum gap. Race Technologies' instructions for Brembo systems give a gap to leave in all directions from the caliper to the wheel. Use the figure from the maker of your kit; we do not repeat one here, because it belongs to the brake.
For a wheel you cannot hold, ask its maker for a drawing of the inner profile and compare it with the brake profile on paper. AP Racing writes that other manufacturers' wheels can often be used, but that the inner wheel profile must be checked.
Can a spacer fix a caliper that touches the spokes?
The two sources disagree, and the difference matters.
| Source | Spacer | Removing material from the caliper or wheel |
|---|---|---|
| AP Racing | Does not recommend a wheel spacer | Does not recommend it |
| Race Technologies (Brembo partner) | A spacer may be used to move the wheel away from the caliper, high-quality and hub-centric only, with longer bolts or studs if needed, and checking the tyre still clears the arches | Not proposed |
A spacer moves the whole wheel outwards: it can cure contact at the spokes, but not contact at the barrel, which is a matter of diameter and barrel shape. It also changes the track and the load on the hub. Our guide to wheel spacers, safety and the law covers what the MOT manual and UK law say. Grinding a caliper or machining the inside of a wheel removes material that was designed to be there; neither brake maker above proposes it.
Big brake kits: check before ordering
Race Technologies states that Brembo performance systems are packaged to order and cannot be returned because of wheel fitment, and that clearance must be confirmed before buying. The order of operations follows:
- Brakes first, wheels second: choose the kit, get its template, then choose wheels that clear it.
- Wheels first, brakes second: send the wheel's inner profile to the brake supplier before ordering.
- Both at once: both suppliers need the other's drawing.
Brake makers often give the wheel size a kit needs: AP Racing, for instance, lists it for each kit. Treat that as a first filter: the template is still the test.
Carbon-ceramic brakes and winter wheels
Carbon-ceramic brakes usually come with large discs and large calipers, and a car maker that offers them can restrict which wheels may be used with them. Check the car maker's wheel and tyre list for your car before buying a second set: a smaller wheel that suits the car with steel brakes may not go over the ceramic ones.
The same question comes back every autumn, when winter tyres go on. A winter set is often chosen one inch smaller than the summer wheels. Whether that inch is possible is decided by the brake, not by the hub or the bolt pattern: a car sold with a bigger brake option can have a smallest permitted wheel that the base car does not. Check the car maker's table for your exact car and brake, then the template. Snow chains add a further question, the space between the tyre and the suspension: Tesla, for example, approves chains by tyre size and for the rear wheels only (Tesla); see snow chains and snow socks and our Tesla Model 3 and Model Y wheels guide.
What else eats into the gap?
- Balance weights. Adhesive weights stuck inside the barrel add their thickness at exactly the place the caliper turns. When clearance is close, check it with the weights in place, and tell the balancer where they may go; wheel balancing explains the planes a balancer works in.
- A different caliper on the same car. Performance versions often have larger brakes than the base car with the same bolt pattern. A wheel that fits one does not prove anything for the other.
- Brake upgrades after the wheels. A new kit or larger discs fitted later restart the check.
Signs that a wheel is touching the brake
A rhythmic scrape or tick that follows road speed, bright marks or paint transfer on the back of the spokes or the top of the caliper, or balance weights that keep disappearing. Stop and have the wheel removed and inspected: a caliper that is rubbing is being worn, and so is the wheel.
A checklist before you buy wheels for a car with big brakes
- Your car's exact brake: standard, optional, or aftermarket, front and rear.
- The brake maker's profile drawing or 1:1 template.
- The brake maker's minimum gap for that kit.
- The wheel's inner profile: barrel and back of the spokes.
- A full-revolution check, every spoke position.
- Balance weight positions, if the margin is small.
- Winter or second set: the smallest wheel the car maker permits with your brakes.
- No spacer as a cure unless the brake maker allows it.
- A trial fit before tyres are mounted, when possible, with the car raised and supported on axle stands, never on the jack alone.
Wheels from Onyx Forged
Onyx Forged wheels are made to order for one car, and the brakes are part of that car. Onyx Forged does not recommend sizes or offsets: the Onyx Forged design office compares the wheel's profile with the dimensions published by the car maker and, for an aftermarket kit, with the brake maker's drawing, and refers you to those documents. If your car has an aftermarket or optional brake kit, tell customer service which one, and send the brake maker's profile drawing if you have it. We do not quote clearance figures or sizes in conversation, because they only mean something for one wheel on one brake. The wheels are designed to JWL/VIA standards.
Frequently asked questions
Will a bigger wheel always clear bigger brakes?
Usually more easily, but not always. The spokes can still touch the outer face of the caliper, which is where AP Racing says contact usually happens.
What is the minimum clearance between a wheel and a caliper?
The figure in the brake maker's fitting instructions for your kit. It is a property of the brake, so check it there rather than using a general number.
Can I use a spacer to clear my calipers?
AP Racing does not recommend it; Race Technologies allows a high-quality hub-centric spacer for spoke contact. A spacer cannot cure contact at the barrel.
Do winter wheels fit over performance or ceramic brakes?
Only if the car maker permits that wheel with those brakes and the template clears. Smaller winter wheels are the usual problem.
Why does my wheel scrape only when turning or braking hard?
In our reading, loads flex the wheel, the hub and the caliper slightly, so a gap that looks sufficient at rest can close under load. Have it inspected rather than driving on it.
Where to go next
For what decides where a wheel sits, read wheel offset; for whether a size suits your car at all, what size wheels fit my car; for spacers, wheel spacers explained. Onyx Forged is a French brand of made-to-order forged wheels, designed to JWL/VIA standards: see Onyx Forged and the catalogue.
Sources
- AP Racing, Inner wheel clearance (big brake kits).
- Race Technologies, How to Measure Your Wheel for Proper Brake Clearance (Brembo official partner).
- Tesla, Model 3 Owner's Manual, Tire Care and Maintenance.
All pages were read on 15 October 2026.
The Onyx Forged design office.