Tire Size Comparison Calculator
Compare two tire sizes side-by-side. See differences in overall diameter, sidewall height, circumference, and speedometer error. Essential for wheel upgrades.
Original Tire
225/45R17
New Tire
235/45R17
How to use Tire Size Comparison Calculator
The tire size calculator decodes the three-number tire code (e.g. 225/45R17) into diameter, sidewall height, circumference and section width, then compares two tire sizes side by side. It also calculates speedometer error so you know how much your indicated speed will differ from actual speed when fitting non-OEM tires.
- Enter the original (stock) tire size in the format Width/Aspect-Ratio/Rim (e.g. 225/45/17).
- Enter the new tire size you are considering.
- Review diameter, sidewall height, circumference and section width for both.
- Check the speedometer error percentage and whether the new tire fits.
Your data never leaves your device — 100% private processing.
Reading a tire size code
A tire code like 225/45R17 means: 225 = tread width in mm; 45 = aspect ratio (sidewall height as a percentage of width, so 45% × 225 = 101.25 mm sidewall); R = radial construction; 17 = rim diameter in inches. Overall diameter = rim diameter (in mm) + 2 × sidewall height. Circumference = π × overall diameter.
| Size | Overall diameter | Sidewall height | Section width |
|---|---|---|---|
| 205/55R16 | 24.9" | 4.5" | 8.1" |
| 225/45R17 | 25.0" | 4.0" | 8.9" |
| 235/50R18 | 27.3" | 4.6" | 9.3" |
| 255/55R18 | 28.0" | 5.5" | 10.0" |
| 265/70R17 | 31.6" | 7.3" | 10.4" |
Speedometer error and safe sizing
A larger-than-stock overall diameter means the car travels further per wheel rotation, so the speedometer reads low (you are going faster than indicated). A smaller diameter reads high. A ±3% difference is considered acceptable by most standards; ±5% affects odometer accuracy and can cause ABS/traction-control calibration issues. Always verify physical clearance (fender, suspension) before fitting significantly different tire sizes.
Glossary
- Aspect ratio
- Sidewall height as a percentage of section width; lower = wider, sportier handling.
- Section width
- The widest point of the tire in millimetres.
- Overall diameter
- The total outer diameter of a mounted, inflated tire.
- Plus sizing
- Fitting a larger-rim tire with a lower-profile sidewall to maintain overall diameter.
Related reading
Frequently Asked Questions
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Why use Tire Size Comparison Calculator?
- Covers all major auto loan and leasing calculations
- Fuel cost comparisons with real MPG/L/100km data
- Instant results with no spreadsheet required
- Supports both metric and imperial units
Common use cases
- Calculate monthly payments on a car loan
- Compare the total cost of owning vs leasing
- Estimate annual fuel costs for a vehicle
- Calculate depreciation over 5 years
- Find out true cost of ownership including insurance
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