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Continue shoppingMAKSTTON WHEEL KNOWLEDGE
How to Measure Wheel Fitment and Calculate the Right Offset
Wheel fitment can feel complicated, especially when choosing the right wheel width and offset for your car.
So we created this simple on-vehicle guide to show you how to collect the essential measurements with basic tools and use our calculator to find a recommended setup. We hope it makes the process a little easier.
Build Your Measurement Sheet as You Go
Follow this guide from top to bottom and enter your vehicle’s specifications and measurements as you go. If a specification is marked on the wheel, enter it directly; otherwise, follow the relevant measurement step or calculator. Your entries will be added automatically to the data sheet at the end, ready to export as a PNG. Gray values are examples from our Cadillac CT4—replace them with information from your own vehicle.
Two rulers, thin string, a small weight, and a phone are enough for the basic measurements. A vernier caliper lets you check Bolt Pattern (PCD) and Hub Pilot Diameter.
Preparation
Prepare the Tools
Basic Tools
- A ruler;
- Thin string and a small weight that can be tied securely and hang vertically;
- A phone for photographs and notes.
Optional Tool
A vernier caliper for measuring Bolt Pattern (PCD) and Hub Pilot Diameter.
Step 1
Set Normal Ride Height
Park the vehicle on level ground, center the steering wheel, and confirm that tire pressures are correct.
If the vehicle has air suspension, set it to the driving height you normally use and record the current suspension mode.
Important: measure fender clearance before lifting the vehicle. After the vehicle has been lifted, its suspension height may remain altered even after it is lowered. Roll the vehicle forward and backward, or drive it briefly, to let the suspension settle again.
Vehicle Information
The vehicle identification or certification label is usually located on a door jamb. Record the following information:
- Make, model, and model year;
- Exact trim or variant;
- Maximum permissible gross mass or GVWR.
Recommended load rating per wheel = GVWR ÷ 4 × 1.2
For large SUVs, off-road vehicles, and heavier EVs, use a factor of 1.3. If the label is unclear, photograph it in full for later review.
Vehicle-label result Make: Cadillac | Build date: June 2021 | Maximum permissible gross mass: 1985 kg. Using the 1.2 factor above, the recommended load rating is at least 595.5 kg; round up to approximately 596 kg per wheel.
Enter Your Vehicle Data
Enter the vehicle information you find on the certification label, then describe the suspension setup and ride-height state used for these measurements.
Record the suspension setup and the ride-height state used for A1 and A2.
Step 2
Measure Fender Clearance
Hang a plumb line from the outer edge at the top of the wheel arch. Once the reference line is steady, use a ruler to record:
- A1: Fender to Rim Edge;
- A2: Fender to Tire Edge.
For air-suspension vehicles, take and record a separate set of measurements at the highest and lowest ride-height settings.
| Spec | Front | Rear |
|---|---|---|
| A1: Fender to Rim Edge | 13 | 14 mm | 15 | 13 mm |
| A2: Fender to Tire Edge | 10 | 11 mm | 12 | 10 mm |
How to record the measurements Record both left and right values for the front and rear axles.
Enter Your Fender Measurements
Enter the left and right measurements separately. They will be combined automatically in the measurement sheet.
Step 3
Record Factory Wheel Specs
Only after measuring fender clearance should you lift the vehicle and remove a wheel. If the front and rear specifications differ, remove one wheel from each axle. If they are identical, one wheel is sufficient.
Locate and record the Wheel Size (diameter × Wheel Width) and Wheel Offset markings, then photograph the tire sidewall clearly to document the complete tire specification.
Complete tire specification225/45 ZR17 94W XL
Capture the tire width, aspect ratio, construction, diameter, load index, and speed rating in the same photograph.
| Spec | Front | Rear |
|---|---|---|
| Wheel Size | 17×8J | 17×8J |
| Offset (ET) | ET32 | ET32 |
| Tire | 225/45 R17 | 225/45 R17 |
| PCD | Not Marked | Not Marked |
| CB | Not Marked | Not Marked |
| Load Rating | Not Marked | Not Marked |
Factory specifications found on this vehicle The front and rear wheel and tire specifications are identical: 17×8J, ET32, 225/45 ZR17 94W XL. If the vehicle uses staggered fitment, remove and document a rear wheel separately. The factory wheel does not show Bolt Pattern (PCD) or Center Bore (CB); with a vernier caliper, continue to the additional measurement method.
Enter Your Factory Wheel Specs
Enter the markings from the wheel and tire. The gray values show the Cadillac CT4 format only; they are not prefilled data.
PCD Marked on the Wheel
If the bolt pattern is stamped or cast into the back of the wheel, enter it here. If it is not marked, use the PCD calculator later in this guide.
Factory Wheel Fastener
Whether the vehicle uses wheel nuts or bolts, take a photograph from the angle shown below so the wheel’s fastener-seat profile can be identified.
Enter Your Fastener Information
Brake-Caliper Projection
If concavity is important, you may also measure caliper projection. This is optional, but recommended for vehicles with upgraded large brake calipers.
- Find the caliper’s outermost point: Locate the part of the caliper that projects farthest outward and lay one ruler across it.
- Read the perpendicular distance: Hold a second ruler perpendicular to the wheel mounting face and read the distance to the first ruler.
Measured caliper projection Result: 10 mm
Enter Your Brake / Caliper Data
Record the brake or caliper setup and the measured projection if available.
Optional
Measure Bolt Pattern (PCD)
The wheel does not have a marked Bolt Pattern (PCD), so it was measured with a vernier caliper. This vehicle has five studs. The diameter of one stud, d, is 11.93 mm, and the outside-to-outside distance between two adjacent studs, s, is 79.4 mm.
Bolt Pattern (PCD) measurement result for this Cadillac5 holes | Stud diameter: 11.93 mm | Outside distance between adjacent studs: 79.4 mm
Calculated result: (79.4 − 11.93) × 1.7013 = 114.79 mm
Final specification: 5×115
Calculated result: (79.4 − 11.93) × 1.7013 = 114.79 mm
Final specification: 5×115
If the vehicle uses wheel bolts, thread two factory bolts lightly into the corresponding holes to the same depth, then measure in the same way. Repeat at several positions and record multiple readings for comparison.
PCD Calculator
Enter your measurements to calculate PCD. For 4-, 5-, or 6-hole patterns, measure the outside-to-outside span across two adjacent studs.
Important
Measure Hub Pilot Diameter
Research and On-Vehicle Measurement
For initial research, use Wheel-Size.com to cross-check factory wheel and tire specifications and the nominal Center Bore (CB) listed for the wheel.
For custom-wheel development, we also measure Hub Pilot Diameter: the outside diameter of the locating lip on the vehicle hub. Center Bore (CB) is the mating hole in the wheel. They are related dimensions, not the same part. A nominal online figure may not match the vehicle; we have measured a hub at 63.26 mm when the listed value was 63.4 mm.
Set the final Center Bore (CB) from the measured Hub Pilot Diameter, with the required assembly clearance and machining tolerance. Do not copy a listing or machine the bore to exactly the hub measurement.
After removing the wheel, clean dirt and corrosion from the hub pilot.
Use the outside jaws of a vernier caliper to measure Hub Pilot Diameter on a full, straight cylindrical surface, avoiding the leading-edge chamfer. Take horizontal and vertical readings, repeat two or three times, and photograph the caliper position and value.
Final value used for this vehicle Hub Pilot Diameter: 70.2 mm
Enter Your Hub Measurement
Enter the measured Hub Pilot Diameter. The unit will be added automatically in the summary.
Final Step
Record the Data
Your measurements appear here automatically as you work through the guide. To change a value, return to its section above; when you are finished, select Export PNG.
Vehicle Data
| Data | Value |
|---|---|
| Vehicle | — |
| GVWR | — |
| Ride Height / Suspension | — |
| Brakes / Caliper | — |
| Fastener | — |
| PCD | — |
| Hub Pilot Ø | — |
Wheel Data
| Spec | Front | Rear |
|---|---|---|
| Wheel / ET | — | — |
| Tire | — | — |
| Load Rating | — | — |
| A1 (mm) | — | — |
| A2 (mm) | — | — |
All set? Export your measurement sheet as a PNG and keep it handy. You’re well on your way to becoming a wheel-fitment expert.
Save the PNG on iPhone or iPad
![MAKSTTON wheel fitment measurement data ready to save]()
If the iOS share sheet is unavailable, touch and hold the image below to save it, or open the full-size PNG in Safari.
Open full-size PNGWheel Fitment Calculator
Once you have the measurements above, use this calculator to preview different wheel sizes and positions.
QUICK FITMENT
Enter Your Measurements to See the Recommended Offset
Enter the factory specifications and your intended wheel size. The calculator will recommend an offset based on the measured space.
1Factory Wheel
in
J
mm
2Fender to Factory Rim Edge
mm
mm
3Tire Extension Beyond Rim Edge
mm
Check the entries. Every value must be a valid number.
4Target Wheel Size
in
J
Enter the factory wheel data and fender clearance to display the factory wheel position.
MAKSTTON BALANCED-FLUSH RECOMMENDATION
20×9.5J ET34.5
Tire inset 5 mm
Current simulation
20×9.5J ET34.5
Tire inset 5 mm
Outside / fender3D position diagram (drag to adjust)Inside
Drag the diagram or slider to adjust positionTire inset 5 mm
Poke 40 mmFlush 0Inset 40 mm
Tire-to-fender positionInset 5 mm
Rim-to-fender positionInset 13 mm
New rim vs. factory7 mm outward
How to use this calculator: The diagram illustrates spatial changes between the tire, rim, and fender; it is not a scale model of the vehicle. The calculation primarily estimates the outer rim position. Before confirming a final specification, rely on measurements from the actual vehicle and verify inner-wheel, suspension, and brake clearance.
Conclusion
Good fitment starts with a few careful measurements.
Once the factory wheel and fender-clearance data are recorded, choosing Wheel Width and Wheel Offset becomes a calculation instead of a guess.
Enter the measurements in the calculator above, choose the intended wheel size, and drag the diagram to compare positions and Wheel Offset values. MAKSTTON’s Balanced Flush recommendation keeps the tire’s outermost edge about 5 mm inside the fender by default, while the slider lets you explore a fuller or more conservative stance.
You are also welcome to send us your vehicle model, photos, and measurements. We are building our own fitment reference, and with your permission, we may include your data after checking it. The measurements you take today could help the next owner of the same model—and save them a lot of time.
Coming Next
For in-house vehicle development, MAKSTTON collects additional measurements with professional tools. A future guide will cover that workflow for workshops that want to collect fitment data efficiently and accurately.
Frequently Asked Questions
How do I measure wheel-to-fender clearance?
Park the vehicle on level ground at normal driving height. Establish a vertical reference line from the outermost fender edge, then measure horizontally to the factory rim edge. If both sides are measured, the calculator automatically uses the smaller clearance.
How do Wheel Width and Wheel Offset affect flush fitment?
Increasing Wheel Width extends the wheel farther both inward and outward. With width unchanged, a lower Wheel Offset moves it outward, while a higher Wheel Offset moves it inward.
Why measure tire extension beyond the rim?
The tire’s outermost edge usually sits beyond the rim edge. Entering this value includes sidewall bulge in the fender-clearance calculation. The default is 5 mm; enter 0 to calculate from the rim edge alone.
Can I copy wheel specs from another car of the same model?
Online references and same-model fitment references can point you in the right direction, but market version, model year, ride height, alignment, tires, and body assembly tolerances can all change the result. Measure your own vehicle before finalizing the specification.
Can I use the calculator’s recommended Wheel Offset to order wheels?
The calculator estimates Wheel Offset mainly from available outer-wheel clearance. Before confirming a final specification, verify inner-wheel clearance, suspension and steering travel, brake-caliper clearance, fasteners, Center Bore (CB), and load capacity.
Binghua Yang | Product Development Manager
Technical data: Renbing Xiong | Technical Department