Tire Size Calculator
Compare two tire sizes to see diameter difference, speedometer error percentage, actual vs indicated speed, clearance change, and revolutions per mile. Visual comparison display helps you choose the right replacement tire size.
Common Tire Sizes (click to apply)
C = set as Current, N = set as New
Tire Specifications
| Measurement | Current | New | Difference |
|---|---|---|---|
| Overall Diameter | 26.63" | 27.18" | +0.55" |
| Circumference | 83.66" | 85.38" | +1.72" |
| Sidewall Height | 5.31" | 5.09" | -0.23" |
| Section Width | 8.86" | 9.25" | +0.39" |
| Revs per Mile | 757 | 742 | -15 |
Visual Size Comparison
Speedometer Reading vs Actual Speed
| Speedo Reads | Actual Speed | Difference |
|---|---|---|
| 20 mph | 20.4 mph | +0.4 mph |
| 30 mph | 30.6 mph | +0.6 mph |
| 40 mph | 40.8 mph | +0.8 mph |
| 50 mph | 51.0 mph | +1.0 mph |
| 60 mph | 61.2 mph | +1.2 mph |
| 70 mph | 71.4 mph | +1.4 mph |
| 80 mph | 81.6 mph | +1.6 mph |
New tires are larger: your speedometer will read LOWER than your actual speed.
How to Use Tire Size Calculator
- 1Enter current tire size
- 2Enter new tire size
- 3View diameter and speedometer differences
- 4Check clearance and width changes
Frequently Asked Questions
How much tire size difference is safe?▾
Stay within 3% of the original tire diameter. Larger differences can affect speedometer accuracy, ABS/traction control calibration, and may cause rubbing on wheel wells. A 3% change equals about 1 mph speedometer error at 30 mph.
What do tire numbers mean?▾
Example: 225/65R17. 225 = width in mm. 65 = aspect ratio (sidewall height as % of width). R = radial construction. 17 = rim diameter in inches. The overall diameter depends on all three numbers.
Will bigger tires affect my speedometer?▾
Yes. Larger diameter tires cause your speedometer to read slower than actual speed. For example, going from 225/65R17 to 235/70R17 increases diameter by about 3.5%, meaning at an indicated 60 mph you are actually going about 62 mph.
About Tire Size Calculator
Compare two tire sizes to see diameter difference, speedometer error percentage, actual vs indicated speed, clearance change, and revolutions per mile. Visual comparison display helps you choose the right replacement tire size.
NexTool's Tire Size Calculator is completely free to use with no sign-up required. Your data is processed directly in your browser and never sent to our servers, ensuring complete privacy and instant results.
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