Rolling Radius Calculator | Get Your Exact Tire Radius Under Load FREE
Calculate your tire's EXACT rolling radius under load! Essential for speedometer accuracy, gear ratios & performance. Enter tire size, get instant results FREE.
The rolling radius of a tire is its effective radius from the center of the axle to the ground when the vehicle is stationary and the tire is under its normal load. It's slightly less than the tire's unloaded (free or static) radius due to the deflection of the tire under the vehicle's weight.
Why is Rolling Radius Important? - **Accurate Speed & Distance:** Vehicle speedometers and odometers are calibrated based on the rolling radius. Changes to this radius (e.g., due to different tire sizes or pressures) can lead to inaccuracies. - **Gearing Calculations:** The effective gear ratio of a vehicle is influenced by the rolling radius. - **Vehicle Dynamics:** It plays a role in suspension geometry and how the vehicle interacts with the road.
This calculator estimates the rolling radius based on standard P-Metric tire dimensions. It first calculates the unloaded radius and then applies a common approximation (typically around 97% of the unloaded radius) to estimate the loaded rolling radius. Actual rolling radius can also be affected by tire pressure, load, speed, and specific tire construction.
- Enter the tire's Section Width in millimeters (e.g., 225).
- Input the tire's Aspect Ratio as a percentage (e.g., 45).
- Enter the Rim Diameter in inches (e.g., 17).
- Click the "Calculate Radius" button.
- The results will display the unloaded (free) radius of the tire and an estimated rolling radius (under load), both in inches and millimeters.
What is rolling radius and why is it important?
Rolling radius is the effective radius from the axle center to the ground when a tire is under load. It's crucial for accurate speedometer readings, odometer calculations, and understanding how tire changes affect vehicle performance and gearing.
How is rolling radius different from tire diameter?
Rolling radius is measured from the axle center to the ground under load, while tire diameter is the overall height of an unloaded tire. Rolling radius is typically smaller due to tire deflection under weight, usually about 97% of the unloaded radius.
Will different tire pressures affect my rolling radius?
Yes, tire pressure significantly affects rolling radius. Lower pressure increases tire deflection, reducing the effective rolling radius. Higher pressure reduces deflection, increasing rolling radius. This calculator uses a standard approximation.
Can I use this calculator for truck or motorcycle tires?
This calculator is designed for P-Metric passenger car tire sizes. For truck tires (LT sizes) or motorcycle tires, the deflection characteristics may differ, so results should be used as estimates only.
How does rolling radius affect my speedometer accuracy?
Changes in rolling radius directly affect speedometer accuracy. If your new tires have a smaller rolling radius, your speedometer will read higher than your actual speed. Larger rolling radius causes the opposite effect.
All tools and information provided on TireCalculatorHub are for informational purposes only. Calculated rolling radius is an estimation. Always consult with a qualified professional or refer to manufacturer specifications for precise data.
TireCalculatorHub is not liable for any damages or issues arising from the use of information or tools on this website.