Tire Size Calculator
Enter the tire code to see how overall diameter, sidewall height, circumference, and revs per mile change when you upgrade wheels or tires.
How to Use This Calculator
Read your tire code
Find the numbers printed on your tire sidewall, such as 245/40R19. The width is the first number, the aspect ratio is second, and the wheel diameter is the number after R.
Enter the values
Type each number into the matching field. You can experiment with potential tire upgrades or winter setups.
Compare the results
Check how the overall diameter, sidewall height, and revolutions per mile change before purchasing new wheels or tires.
Formula
Overall Diameter = Wheel Diameter + 2 × (Width × Aspect Ratio ÷ 100 ÷ 25.4)
Sidewall Height: Width × Aspect Ratio ÷ 100 ÷ 25.4
Circumference: Diameter × π
Revolutions per Mile: 63,360 ÷ Circumference (inches)
Example: 245/40R19 → Sidewall = 245 × 0.40 ÷ 25.4 = 3.86 in → Diameter = 19 + 2 × 3.86 = 26.72 in → Revs/mile = 63,360 ÷ (26.72 × π) = 754
About the Tire Size Calculator
Tire size changes affect ride height, speedometer accuracy, and gearing. This tool helps you visualize those differences so you can select compatible sizes that maintain safety and performance.
When to Use This Calculator
- Wheel upgrades: Check the impact of larger wheels or lower-profile tires before buying.
- Seasonal setups: Compare winter tires to summer sizes and maintain similar rolling diameter.
- Performance tuning: Understand how diameter changes affect effective gearing.
- Speedometer corrections: Use the revs per mile to recalibrate speedometers or odometers.
Why Use Our Calculator?
- ✅ Accurate conversions: Uses metric-to-imperial mechanics to mirror tire industry math.
- ✅ Revs per mile: Quickly compare OEM speedometer calibration to your new tires.
- ✅ Mobile friendly: Plan purchases from the tire shop or garage.
- ✅ Free: Experiment with as many combinations as you like.
Common Applications
Track day drivers: Confirm how alternate tire sizes influence gearing and lap times.
Off-road builds: Calculate clearance changes when moving to larger tires.
Fleet managers: Standardize rolling diameters across different vehicles.
Tips for Best Results
- Use published rolling diameter from tire manufacturers for the most precise revs per mile.
- Verify fender and suspension clearance when increasing diameter or width.
- Keep overall diameter within ±3% of stock to maintain speedometer accuracy.
- Adjust tire pressure according to manufacturer recommendations after changing sizes.
Frequently Asked Questions
How much can I change tire diameter without issues?
Most manufacturers recommend staying within ±3% of the original diameter to maintain speedometer accuracy and avoid clearance problems.
Does this calculator account for tire load?
It assumes static dimensions. Under load, the tire flattens slightly, reducing effective diameter. Consult manufacturer data for precise rolling radius.
How do staggered setups affect results?
Calculate front and rear tires separately. Matching overall diameter helps keep traction control, ABS, and AWD systems happy.
Will my speedometer change?
Yes. If you increase diameter, your speedometer will read slightly slower than actual speed. Use revs per mile to determine correction factors.