Tire Size Comparison
1 Current / Reference Tire
metric
Format: Section Width (mm) / Aspect Ratio (%) R Rim Diameter (inches)
2 New / Comparison Tire
metric
Format: Section Width (mm) / Aspect Ratio (%) R Rim Diameter (inches)
0.0%
Difference in Diameter
Diameter Difference Scale
Tire 1
Tire 2
| Specification | Tire 1 | Tire 2 | Difference |
|---|
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How to Use the Tire Size Comparison Calculator
Enter two tire sizes in the standard metric format: Section Width / Aspect Ratio R Rim Diameter. For example, 245/45R18 means 245mm tread width, 45% aspect ratio, radial construction, 18-inch rim.
The calculator compares every measurement and shows the percentage difference between the two tires. A diameter difference under 3% is generally considered a safe swap.
Understanding the Comparison Results
- Tire Diameter - The overall height. Changing this affects ground clearance and speedometer accuracy.
- Section Width - The tread width. Wider tires may rub on suspension or bodywork.
- Sidewall Height - Distance from rim to tread. Affects ride comfort and handling.
- Circumference - Distance traveled per revolution. Directly impacts speedometer readings.
- Revolutions per Mile - How many times the tire rotates per mile.
- Speedometer Error - How much your speedometer will be off with the new tires.
Key Formula:
Sidewall (in) = (Section Width × Aspect Ratio ÷ 100) ÷ 25.4
Diameter (in) = Rim Diameter + 2 × Sidewall Height
Circumference (in) = π × Diameter
Sidewall (in) = (Section Width × Aspect Ratio ÷ 100) ÷ 25.4
Diameter (in) = Rim Diameter + 2 × Sidewall Height
Circumference (in) = π × Diameter
Is It Safe to Change Tire Size?
The 3% rule is the industry standard. If the new tire's diameter is within 3% of the original, the swap is generally safe. Beyond 3%, you may experience inaccurate speedometer, reduced clearance, gearing changes, and potential issues with ABS and traction control.
Frequently Asked Questions
Tire sizes use the metric format XXX/XX RXX. The first three digits are the section width in millimeters. The next two are the aspect ratio - sidewall height as a percentage of width. The 'R' means radial construction. The final number is the rim diameter in inches.
Most manufacturers allow up to 3-5% speedometer error. When changing tire size, keeping the diameter within 3% of the original ensures the speedometer stays reasonably accurate.
You can typically go up or down by 10-20mm in width on the same rim, but always check the rim width range for the tire size. Going too wide can cause the tire to bulge improperly.
Yes. Larger and wider tires increase rolling resistance and weight, which can reduce fuel economy. Taller tires also change your final drive ratio, potentially causing the engine to work harder at highway speeds.
Plus-sizing increases rim diameter while reducing tire sidewall height to keep the overall diameter the same. For example, going from 205/55R16 to 225/45R17 (Plus 1) or 225/40R18 (Plus 2).