About Tire Size Comparison & Speedometer Error
Visual tire size comparison tool. Parse metric tire sizes (e.g., 225/45R17 vs 245/40R18), calculate sidewall height, overall diameter, revolutions per mile, ride height change, and complete speedometer error speed tables.
Key Capabilities & Features
- Full metric tire specification parser (e.g., 225/45R17, 245/40R18, 275/35R19)
- Side-by-side comparison of section width, sidewall height, overall diameter, and revolutions/mile
- Ride height and ground clearance variation calculation
- Speedometer reading discrepancy table across 20 to 80 mph
- Automated fitment safety advisory warning if diameter change exceeds ±3% threshold
How to Use Tire Size Comparison & Speedometer Error
Input OEM Tire Size
Enter original factory tire size (e.g., 225/45R17).
Input New Tire Size
Enter proposed aftermarket tire size (e.g., 245/40R18).
Review Fitment Advisory
Check if diameter variance is within the safe 1.5% - 3.0% threshold.
Check Speedometer Error
See how your speedometer reading will differ from actual road speed.
Privacy & In-Browser Execution Guarantee
100% client-side calculation. Your data never leaves your browser.
Frequently Asked Questions
What does 225/45R17 mean?
225 is the section width in millimeters, 45 is the aspect ratio (sidewall height is 45% of width), R indicates radial construction, and 17 is the wheel rim diameter in inches.
What is the maximum safe tire diameter change?
Automakers and tire manufacturers recommend keeping overall tire diameter within ±3% (ideally ±1.5%) of OEM to prevent ABS, traction control, and transmission shifting errors.