Vehicle Tools
Tire Size Comparison Calculator
Tire sizes look cryptic, but the numbers can be translated into sidewall height and overall diameter. This calculator compares your original tire size with a new size to show the difference in inches and percent.
Planning note
How this calculation works
- Sidewall height is tire width multiplied by aspect ratio.
- Overall diameter is wheel diameter plus two sidewalls converted from millimeters to inches.
- Speedometer effect is estimated from the percentage diameter change.
Assumptions and limitations
- Actual tire dimensions vary by brand, model, tread depth, load rating, and measurement method.
- This does not check wheel width, load index, speed rating, clearance, rubbing, ABS, AWD, or manufacturer guidance.
- Consult your owner's manual, tire placard, tire shop, or manufacturer before changing sizes.
Worked example
A 225/65R17 tire has a different overall diameter than a 235/60R18. A small percentage difference may be acceptable in some cases, but clearance and rating still matter.
FAQ
What does 225/65R17 mean?
225 is width in millimeters, 65 is sidewall height as a percent of width, and 17 is wheel diameter in inches.
How much difference is too much?
Many shoppers try to keep diameter changes small, but your vehicle manufacturer or tire professional should guide the final decision.
Can a tire fit because the diameter is close?
Not necessarily. Width, wheel offset, suspension clearance, load rating, and turning clearance also matter.
Will this affect my speedometer?
Yes. A larger diameter can make actual speed higher than indicated; a smaller diameter can do the opposite.