Tyre Size Comparison Calculator
Original Tyre Size
e.g., for 205/55 R16:
New Tyre Size
e.g., for 225/45 R17:
Calculation Results
| Metric | Original Tyre | New Tyre | Difference | % Change |
|---|---|---|---|---|
| Sidewall Height (mm) | – | – | – | – |
| Tyre Diameter (mm) | – | – | – | – |
| Tyre Circumference (mm) | – | – | – | – |
| Speedometer Error | – | – | – | – |
Understanding Your Tyre Size and Fitment
Changing your vehicle's tyre size might seem straightforward, but it involves several critical considerations that can impact safety, performance, and even your car's electronics. Our Tyre Size Comparison Calculator helps you understand the precise differences between your original and potential new tyre sizes.
Decoding Tyre Sizing (e.g., 205/55 R16)
- 205: This is the Tyre Width in millimeters. It measures the width of the tyre from sidewall to sidewall.
- 55: This is the Aspect Ratio, expressed as a percentage. It represents the sidewall height as a percentage of the tyre's width. In this example, the sidewall height is 55% of 205mm.
- R: Indicates a radial construction tyre, which is standard for most modern vehicles.
- 16: This is the Rim Diameter in inches. It specifies the diameter of the wheel that the tyre is designed to fit.
Why Tyre Fitment Matters
Even small changes in tyre dimensions can have significant effects:
- Speedometer Accuracy: If the new tyre's overall diameter is different from the original, your speedometer will read incorrectly. A larger diameter tyre will make your speedometer read lower than your actual speed, while a smaller one will make it read higher. Most experts recommend keeping the diameter difference within +/- 3%.
- Fender Clearance: A wider or taller tyre might rub against your vehicle's fenders, suspension components, or brake lines, especially during turns or when the suspension compresses.
- ABS/ESP Systems: Modern vehicles rely on precise wheel speed sensor readings for Anti-lock Braking Systems (ABS) and Electronic Stability Programs (ESP). Significant changes in tyre diameter can confuse these systems, potentially leading to malfunctions or reduced effectiveness.
- Ride Comfort and Handling: Changes in sidewall height directly affect ride comfort and handling characteristics. A lower aspect ratio (shorter sidewall) generally means stiffer handling but a harsher ride.
- Load Capacity: Ensure the new tyres have an adequate load index for your vehicle's weight.
How to Use the Calculator
- Enter Original Tyre Details: Input the width, aspect ratio, and rim diameter of the tyres currently on your vehicle. You can find this information on the tyre's sidewall or in your car's owner's manual.
- Enter New Tyre Details: Input the dimensions of the new tyre size you are considering.
- Click "Calculate Tyre Fit": The calculator will instantly display key metrics for both tyres, including sidewall height, overall diameter, and circumference.
- Review Differences: Pay close attention to the "Difference" and "% Change" columns. The speedometer error is particularly important.
- Check Warnings: The calculator will provide a warning if the diameter change exceeds generally recommended limits, indicating a potential issue.
General Guidelines for Tyre Size Changes
While this calculator provides valuable data, always consult with a professional tyre specialist before making significant changes. As a rule of thumb:
- Keep the overall tyre diameter change within +/- 3% to minimize speedometer error and potential clearance issues.
- Ensure the new tyre's load index and speed rating meet or exceed your vehicle's requirements.
- Consider the impact on your vehicle's aesthetics and driving dynamics.
Using this calculator is a great first step in making an informed decision about your next set of tyres!