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Calculate tire size differences, compare dimensions, check speedometer accuracy & compatibility. Free tire calculator with diameter, circumference & fitment guide.
Click to load a preset tire size
Input your current tire size (e.g., 205/55R16). Find it on your tire sidewall or vehicle manual.
Input the tire size you're considering (e.g., 215/60R16). Compare multiple options easily.
See diameter difference, speedometer impact, and fitment recommendations instantly.
Learn to read and understand tire size format
The first number (e.g., 205) represents the tire width in millimeters from sidewall to sidewall. Wider tires generally provide better grip but may reduce fuel efficiency.
The second number (e.g., 55) is the aspect ratio - the sidewall height as a percentage of the width. A 55 aspect ratio means the sidewall height is 55% of 205mm = 112.75mm.
The last number (e.g., 16) indicates the wheel diameter in inches that the tire is designed to fit. This must match your wheel size exactly.
Overall tire diameter affects speedometer accuracy, ground clearance, and vehicle performance. Keep within ±3% for optimal safety and functionality.
Tire circumference determines how far your vehicle travels per wheel revolution. Larger circumference means fewer revolutions per mile/kilometer.
Your speedometer is calibrated for original tire size. Changing tire size affects accuracy because the vehicle travels a different distance per wheel revolution.
Larger Tires: Speedometer reads LOWER than actual speed
Smaller Tires: Speedometer reads HIGHER than actual speed
Formula: Actual Speed = Indicated Speed × (New Diameter ÷ Original Diameter)
Example: 3% larger tire at indicated 100 km/h = actual 103 km/h
Impact: You could get speeding tickets without realizing it!
✅ 0-3% difference: Acceptable, minimal impact
⚠️ 3-5% difference: Noticeable, consider recalibration
❌ Over 5% difference: Significant error, recalibration required
Keep diameter difference within ±3% of original size for optimal performance and safety.
3-5% difference may work but requires careful consideration of clearance and handling.
Over 5% difference can cause serious issues with speedometer, handling, and safety systems.
Plus sizing means increasing wheel diameter while decreasing sidewall height to maintain similar overall diameter. Example: 205/55R16 to 205/50R17 (+1 sizing). Improves handling but may reduce ride comfort.
Check clearance at full steering lock and suspension compression. Larger tires may rub against fenders, suspension components, or frame. Test drive before final installation.
Ensure adequate space in wheel wells for tire movement. Consider lift kits or fender modifications for significantly larger tires. Consult tire professional for vehicle-specific recommendations.
Prevent costly mistakes by checking compatibility before purchase. Ensure tires fit without rubbing or clearance problems.
Know exactly how tire size changes affect speedometer readings. Avoid speeding tickets and maintain accurate odometer readings.
Choose tire sizes that enhance handling, comfort, or off-road capability based on your needs. Make informed decisions for better performance.
Stay within safe tolerance ranges for diameter differences. Protect ABS, traction control, and other safety systems from malfunction.
Convert between metric (205/55R16) and inch-based sizing (26.5x8.1R16). Useful for comparing different tire formats.
Example: 205/55R16 = approximately 26.5 inches diameter × 8.1 inches width
P-metric (P205/55R16) for passenger vehicles, Euro-metric (205/55R16) without P prefix. Slight load capacity differences.
Note: P-metric tires typically have slightly lower load capacity than Euro-metric
LT tires (LT265/70R17) for trucks and heavy-duty vehicles. Reinforced construction, higher load capacity, require higher pressure.
Example: LT265/70R17 vs P265/70R17 - LT version has stronger sidewalls
Larger/wider tires increase rolling resistance and weight, reducing fuel efficiency by 1-3 mpg. Smaller tires may improve economy slightly.
Tip: Stick to manufacturer recommendations for best fuel economy
Wider tires improve grip and cornering. Lower aspect ratios enhance handling but reduce comfort. Taller sidewalls provide smoother ride.
Balance: Choose based on driving style - performance vs comfort
Larger diameter tires increase ground clearance, beneficial for off-roading. Smaller tires lower vehicle, improving aerodynamics.
Example: 2-inch larger tire = 1-inch more ground clearance
Larger tires make odometer read LOWER mileage than actual. Affects resale value, warranty, and maintenance schedules.
Impact: 3% larger tire = 3% less recorded mileage
Popular truck sizes. 275 is 10mm wider, slightly taller. Minimal speedometer impact (1.5%). Better for off-road, slight fuel economy reduction.
Common sedan upgrade. 215 is 10mm wider, same aspect ratio. Improves grip, minimal diameter change (0.8%). Check wheel well clearance.
Off-road sizes. 33-inch is 2 inches taller, 2 inches wider. Requires lift kit. Significant speedometer impact (6.5%). Better ground clearance.
Our tire size calculator uses industry-standard formulas verified by automotive engineering principles. All calculations follow the same methods used by tire manufacturers and automotive professionals worldwide.
Based on SAE (Society of Automotive Engineers) standards for tire measurements and dimensional calculations.
Our recommendations prioritize vehicle safety, following manufacturer guidelines and industry best practices.
Comprehensive guides help you understand tire sizing, ensuring informed decisions for your vehicle.
Important: While our calculator provides accurate measurements and recommendations, always consult your vehicle's owner manual and a qualified tire professional before making final tire purchase decisions. Vehicle-specific factors like suspension modifications, wheel well clearance, and load requirements should be professionally evaluated.
Tire size format (e.g., 205/55R16) breaks down as follows: 205 represents the tire width in millimeters, 55 is the aspect ratio (sidewall height as a percentage of width), R indicates radial construction, and 16 is the rim diameter in inches. For example, a 205/55R16 tire is 205mm wide with a sidewall height of 112.75mm (55% of 205mm) designed to fit a 16-inch rim.
For optimal safety and vehicle function, keep the overall diameter difference within ±3% of the original tire size. A difference of 3-5% may be acceptable but requires careful consideration of clearance and handling. Differences exceeding 5% are not recommended as they can cause speedometer errors, handling issues, and problems with ABS and traction control systems. Always check vehicle clearance and consult manufacturer recommendations.
Tire size directly impacts speedometer accuracy. Larger tires cause the speedometer to read lower than your actual speed (meaning you're traveling faster than displayed). Smaller tires cause it to read higher than actual speed. The formula is: Actual Speed = Indicated Speed × (New Diameter ÷ Original Diameter). For example, with a 3% larger tire, if your speedometer shows 100 km/h, your actual speed is 103 km/h.