Compare Tire Sizes
Enter tire sizes using standard notation (Width/Aspect-Ratio/Rim-Diameter) to compare specifications and see how changing tire size affects your speedometer reading.
Original Tire
New Tire
Original Tire Specifications
Overall Diameter
Circumference
Sidewall Height
Revolutions per Mile
New Tire Specifications
Overall Diameter
Circumference
Sidewall Height
Revolutions per Mile
Comparison Results
Popular Tire Sizes Reference
Common tire sizes and their dimensions for quick reference.
| Tire Size | Diameter | Circumference | Sidewall | Common Vehicle |
|---|---|---|---|---|
| 195/65R15 | 25.0 in | 78.5 in | 5.0 in | Compact cars |
| 205/55R16 | 24.9 in | 78.2 in | 4.4 in | Midsize sedans |
| 215/60R16 | 26.2 in | 82.2 in | 5.1 in | Sedans, wagons |
| 225/65R17 | 28.5 in | 89.6 in | 5.8 in | SUVs, crossovers |
| 235/45R18 | 26.3 in | 82.6 in | 4.1 in | Sports cars |
| 235/75R15 | 28.9 in | 90.7 in | 6.9 in | Light trucks |
| 265/70R17 | 31.6 in | 99.4 in | 7.3 in | Trucks, large SUVs |
| 285/75R16 | 32.8 in | 103.1 in | 8.4 in | Heavy-duty trucks |
How Tire Size Affects Your Vehicle
Understanding Tire Notation
Tire sizes are written as WIDTH/ASPECT-RATIO R RIM-DIAMETER. For example, 225/65R17 means:
- 225 - Section width in millimeters (widest point of the tire)
- 65 - Aspect ratio (sidewall height as percentage of width)
- R - Radial construction (standard for modern tires)
- 17 - Rim diameter in inches
Calculation Formulas
The calculator uses these formulas to compute tire dimensions:
- Sidewall height = (Width in mm × Aspect ratio) ÷ 100 ÷ 25.4
- Overall diameter = (2 × Sidewall height) + Rim diameter
- Circumference = Diameter × π (3.14159)
- Revolutions per mile = 63,360 ÷ Circumference
Speedometer Impact
When you install tires with a different diameter, your speedometer reading becomes inaccurate because it is calibrated for the original tire size. A larger tire travels further with each revolution, meaning your actual speed is higher than indicated. A smaller tire has the opposite effect.
Most experts recommend staying within 3% of the original tire diameter to maintain accurate speedometer readings and avoid issues with vehicle systems like ABS and traction control.
Ground Clearance Change
The ground clearance change is half the difference in overall diameter. A larger tire raises your vehicle, potentially improving off-road capability but affecting handling and fuel economy. A smaller tire lowers the vehicle.
Frequently Asked Questions
How much can I change tire size without issues?
Most vehicle manufacturers and tire experts recommend staying within 3% of the original tire diameter. Changes within this range typically will not affect speedometer accuracy, ABS, traction control, or other vehicle systems. Larger changes may require recalibration of vehicle electronics.
Will larger tires affect my gas mileage?
Yes. Larger tires are heavier and have more rolling resistance, which typically reduces fuel economy by 1-3 mpg depending on size increase. They also change your effective gear ratio, forcing the engine to work harder to maintain the same speed.
How do I fix my speedometer after changing tire size?
If you change tire size beyond the recommended 3% tolerance, you have several options: install a speedometer recalibration device, use a GPS-based speedometer app, have your vehicle's computer reprogrammed at a dealer, or install a gear ratio adapter in the transmission. The best option depends on your vehicle and budget.
What happens if I use different size tires front and rear?
Some vehicles (especially sports cars and performance vehicles) come with staggered setups from the factory with different sizes front and rear. However, on vehicles not designed for this, it can cause drivetrain damage on all-wheel-drive and four-wheel-drive systems. Always consult your owner's manual before running different size tires.
Can I use wider tires on the same rim?
Each rim width has a range of compatible tire widths. Installing tires that are too wide for your rim can cause poor handling, accelerated wear, and potential safety issues. Consult a tire width chart for your rim size to determine safe options, or ask a tire professional.
Do larger tires improve off-road performance?
Larger tires can improve off-road capability by increasing ground clearance and providing better obstacle clearance. However, they also add weight, reduce acceleration, may require suspension modifications, and can strain drivetrain components. For serious off-roading, a complete vehicle setup including suspension, gearing, and tire selection should be considered.
Will changing tire size affect my warranty?
It depends on the manufacturer and the extent of modification. Most manufacturers allow tire size changes within their approved size ranges without voiding warranty. However, installing significantly oversized tires or making related modifications like suspension lifts may void certain warranty coverages, particularly for drivetrain components.
Does this calculator work for motorcycle tires?
Yes, the basic calculations work for any tire that uses the standard WIDTH/ASPECT-RATIO R RIM-DIAMETER notation. However, some motorcycle tires use different sizing systems (like 120/70-17 or older inch-based sizes), and the practical considerations for motorcycles differ from cars and trucks.
Privacy & Limitations
- All calculations run entirely in your browser -- nothing is sent to any server.
- Results are estimates and may vary based on actual conditions.
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Tire Size Calculator FAQ
What is Tire Size Calculator?
Tire Size Calculator is a free utility & everyday tool that helps you Compare tire sizes and calculate speedometer differences.
How do I use Tire Size Calculator?
Enter your input values, review the calculated output, and adjust inputs until you reach the result you need. The result updates in your browser.
Is Tire Size Calculator private?
Yes. Calculations run locally in your browser. Inputs are not uploaded to a server by default, and refreshing the page clears session data.
Does Tire Size Calculator require an account or installation?
No. You can use this tool directly in your browser without sign-up or software installation.
How accurate are results from Tire Size Calculator?
This tool applies standard formulas or deterministic processing logic for estimates. For medical, legal, tax, or investment decisions, verify with a qualified professional.
Can I save or share outputs from Tire Size Calculator?
You can bookmark this page and copy outputs manually. Results are not persisted in your account and are typically not embedded in the URL.