Automotive
Tire Size Calculator
Use our free Tire Size Calculator to convert, compare, and understand tire dimensions. Perfect for vehicle owners, mechanics, and car enthusiasts to ensure the right fit and performance.
Why Compare Tire Sizes?
Switching to a different tire size affects your vehicle's speedometer accuracy, ground clearance, handling, fuel economy, and ride comfort. Even small changes in diameter can cause your speedometer to read incorrectly — leading to speeding tickets or inaccurate odometer readings.
This calculator computes diameter, sidewall height, circumference, revolutions per mile, and the speedometer error between your original and new tire sizes. A difference within ±3% is generally considered safe.
Original Tire Size
New Tire Size
How to Use This Calculator
- Enter your current tire's width, aspect ratio, and rim size
- Enter the new tire's width, aspect ratio, and rim size
- Click Compare Tire Sizes
- Review diameter change, speedometer error, and compatibility
- Keep speedometer error within ±3% for safe fitment
Common Use Cases
- Upgrading to larger rims
- Plus-sizing tires
- Winter tire selection
- Off-road tire fitting
- Speedometer calibration
- Finding equivalent sizes
How to Read a Tire Size (e.g. 225/60R16)
| Component | Example | Meaning |
|---|---|---|
| Section Width | 225 | Tread width in millimeters |
| Aspect Ratio | 60 | Sidewall height as % of width (225 × 0.60 = 135mm) |
| Construction | R | Radial construction (most common) |
| Rim Diameter | 16 | Wheel diameter in inches |
Popular Tire Sizes by Vehicle Type
| Vehicle Type | Common Sizes | Typical Rim |
|---|---|---|
| Compact Car | 185/65R15, 195/55R16 | 15–16" |
| Sedan / Midsize | 205/55R16, 215/55R17 | 16–17" |
| SUV / Crossover | 225/65R17, 235/60R18 | 17–19" |
| Pickup Truck | 265/70R17, 275/65R18 | 17–20" |
| Sports Car | 225/40R18, 245/35R19 | 18–20" |
| Off-Road / 4×4 | 265/75R16, 285/70R17 | 16–17" |
FAQ – Tire Size Calculator
What is a Tire Size Calculator?
A Tire Size Calculator helps you compare and understand tire dimensions, such as width, aspect ratio, and rim diameter. It calculates diameter, circumference, and speedometer error when switching sizes.
What do the tire size numbers mean?
In a size like 225/60R16: 225 is the tread width in mm, 60 is the aspect ratio (sidewall height as % of width), R means radial construction, and 16 is the rim diameter in inches.
How does changing tire size affect my speedometer?
A larger tire covers more ground per revolution, making your speedometer read lower than actual speed. A smaller tire does the opposite. The calculator shows the exact error percentage.
What is an acceptable tire size difference?
Most manufacturers recommend staying within ±3% of the original tire diameter. This keeps speedometer error minimal and avoids clearance or handling issues.
What is plus-sizing?
Plus-sizing means increasing rim diameter while decreasing sidewall height to maintain the same overall tire diameter. For example, going from 205/55R16 to 225/45R17. This improves handling but may reduce ride comfort.
Does tire size affect fuel economy?
Yes. Wider tires increase rolling resistance and can reduce fuel economy by 1–3%. Larger diameter tires change the effective gear ratio, which can also impact efficiency.
Can I use a different rim size?
Yes, but you must adjust the tire's aspect ratio to maintain a similar overall diameter. The calculator helps you find the right combination for your new rim size.
How does tire size affect ground clearance?
The ground clearance change equals half the diameter difference. A tire that's 20mm larger in diameter adds 10mm of ground clearance, and vice versa.
What are revolutions per mile?
This measures how many times a tire rotates to cover one mile. Smaller tires have more revolutions (wear faster), while larger tires have fewer revolutions per mile.
How accurate is this calculator?
Calculations are based on standard tire geometry formulas and are very accurate for comparing sizes. Actual dimensions may vary slightly by manufacturer and tire pressure.