Review wheel fitment with clear size comparisons. Check offset, poke, clearance, and diameter shifts. Export results for planning, audits, and maintenance records.
| Case | Current Setup | New Setup | Diameter Change | Outer Poke | Status |
|---|---|---|---|---|---|
| A | 225/45R18, 18x8 ET35 | 235/40R19, 19x8.5 ET40 | 0.80 mm | 1.35 mm | Likely acceptable |
| B | 215/55R17, 17x7 ET45 | 245/45R18, 18x8.5 ET35 | 24.30 mm | 22.70 mm | Possible interference |
| C | 205/60R16, 16x6.5 ET42 | 215/55R17, 17x7 ET40 | 2.90 mm | 8.35 mm | Likely acceptable |
Sidewall Height = Tire Width × (Aspect Ratio ÷ 100)
Overall Diameter = Rim Diameter × 25.4 + 2 × Sidewall Height
Circumference = π × Overall Diameter
Inner Position = (Wheel Width in mm ÷ 2) + Offset
Outer Position = (Wheel Width in mm ÷ 2) − Offset
Inner Clearance Change = New Inner Position − Current Inner Position
Outer Poke Change = New Outer Position − Current Outer Position
Speedometer Error = ((New Circumference ÷ Current Circumference) − 1) × 100
A wheel size fitment calculator helps compare a current setup with a proposed one. It estimates how a new wheel and tire package may change diameter, clearance, and outer position. That makes it useful for planning upgrades with fewer surprises.
The calculator studies wheel width, wheel diameter, offset, tire width, aspect ratio, and rim size. These values affect inner clearance near suspension parts and outer poke near the fender. They also change sidewall height and rolling diameter.
First, the tool converts tire width and aspect ratio into sidewall height. Then it adds the wheel diameter in millimeters to find overall tire diameter. Circumference comes next. That value is important because it affects speedometer reading and rolling distance.
Fitment is not only about tire diameter. Offset and wheel width change where the wheel sits. A wider wheel or lower offset can push the setup outward. A higher offset can move it inward. Both movements matter when checking body and suspension space.
This page also supports comparison based review. You can test several setups and compare the measured differences. That helps with repeatable evaluation. It is useful when you want a clean method for observing change across multiple wheel and tire options.
A small diameter difference usually keeps speedometer error lower. Large inner clearance losses may cause suspension contact. Large outer poke may create rubbing at the fender. The estimated status in this calculator is a screening aid. Final fitment still depends on the vehicle.
Use the CSV option for quick recordkeeping. Use the PDF option for sharing a clean summary. The result table appears directly below the header, so important values stay easy to review after every submission.
Offset change shows how the wheel mounting face moves the wheel inward or outward. It strongly affects suspension clearance and fender position.
Overall diameter affects ride height, speedometer reading, and gear behavior. Large changes can also increase rubbing risk during turns or compression.
Outer poke is how far the new wheel sits outward compared with the current setup. More poke can increase fender interference risk.
Inner clearance change estimates how much closer the new setup moves toward suspension parts. Positive loss means less space remains inside.
Not always. Tire width matters, but wheel width, offset, sidewall shape, alignment, and vehicle suspension movement also affect real rubbing behavior.
Yes. The calculator estimates circumference change and speedometer error. It gives a fast screening value for comparing one setup against another.
No. It is an estimate based on entered dimensions. Brake clearance, alignment, load, and vehicle specific geometry still need confirmation.
Exports help you store comparisons, share setup options, and review repeated tests. They are useful for workshops, enthusiasts, and maintenance planning.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.