Tire Size Comparison
Enter two tire sizes (e.g. 225/45R17) to automatically calculate and compare all dimensions and speedometer deviation
Current Tire
New Tire
Side-by-Side Tire Comparison
Comparison Results
| Parameter | Current | New | Difference |
|---|
Tire Size Explained
Tire sizes are typically marked in the format Width/Aspect RatioR Rim Diameter, for example 225/45R17:
- 225 β Tread width in millimeters
- 45 β Aspect ratio, the sidewall height as a percentage of tread width (45%)
- R β Radial tire construction
- 17 β Rim diameter in inches
Formulas
Sidewall Height = Width Γ Aspect Ratio Γ· 100
Tire Diameter = Rim Diameter Γ 25.4 + Sidewall Height Γ 2
Circumference = Diameter Γ Ο
Revolutions per km = 1,000,000 Γ· Circumference (mm)
Speedometer Error = (New Diameter Γ· Original Diameter - 1) Γ 100%
Common Tire Sizes Reference
| Size | Width (mm) | Sidewall (mm) | Diameter (mm) | Circumference (mm) | Revs/km |
|---|
FAQ
How to read tire size?
For 225/45R17: 225=tread width in mm, 45=aspect ratio (sidewall height as percentage of tread width), R=radial construction, 17=rim diameter in inches. Overall diameter = rim diameter + 2 Γ sidewall height = 17 Γ 25.4 + 2 Γ 225 Γ 0.45 = 634.3mm.
Will changing tire size affect my speedometer?
Yes. If the new tire diameter is larger than stock, your actual speed will be faster than what the speedometer reads, and vice versa. Generally, diameter difference should not exceed 3% to avoid speedometer inaccuracy and ABS/ECU issues. This calculator automatically computes the speedometer deviation percentage.
How much tire diameter difference is acceptable?
The industry standard is that the diameter difference between old and new tires should not exceed Β±3%. Exceeding 3% can cause speedometer inaccuracy, wheel well interference, and suspension stress changes. This tool automatically flags whether the difference is within the safe range.
Is a lower aspect ratio always better?
Not necessarily. Low aspect ratio tires (e.g. 35, 40) provide sharper road feel and better cornering support, but ride comfort is reduced and rims are more vulnerable to damage. High aspect ratio tires (e.g. 60, 65) offer better comfort and cushioning but slower steering response. Choose based on your driving needs and vehicle type.