Tire Size Calculator
Calculate sidewall height, overall tire diameter, circumference and revolutions per mile from a metric tire size such as 245/45R17. Compare two tire sizes to see gearing-related changes.
Tire geometry calculator
Diameter = wheel diameter × 25.4 + 2 × sidewall
Rev/mile = 63,360 ÷ (π × diameter in inches)
Tire comparison
| Metric | A | B | B − A |
|---|---|---|---|
| Diameter | — | — | — |
| Circumference | — | — | — |
| Rev/mile | — | — | — |
Worked example
Why tire diameter matters
A larger effective tire diameter increases road speed at a given engine RPM and reduces engine RPM at a given road speed. A smaller diameter does the opposite. Tire diameter also affects speedometer calibration and effective gearing.
Important: nominal tire dimensions are not the same as measured loaded diameter. Pressure, load, construction and wear can change the effective rolling radius.
Recommended Tools for Tire & Wheel Fitment
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Accurate tire and wheel fitment requires more than calculated dimensions. These tools can help verify wheel measurements, bolt patterns, and available clearance before purchasing or installing components.
Atesilor Wheel Fitment Tool
Wheel Offset & Backspacing Measurement
Verify wheel offset and backspacing changes before installing new wheels. Compare how a wheel may move inward or outward relative to suspension and fender clearance.
View on AmazonFIRSTINFO Wheel Bolt Circle Gauge
Bolt Pattern Measurement
Measure lug spacing and bolt circle patterns to confirm wheel compatibility before purchasing or installing wheels.
View on AmazonCRAFTSMAN 25-Foot Tape Measure
Clearance Measurement
Measure tire diameter, wheel-well clearance, and available space around suspension and body components when evaluating fitment changes.
View on Amazon