Compare tire sizes with advanced calculations, speedometer corrections, and performance analysis. Get professional-grade results with real-time updates and safety compliance checks.
Current Size: 225/65R17
New Size: 235/60R18
✅ Tire size change is within safe parameters
Master tire sizing with our professional-grade calculator. Learn tire mathematics, speedometer corrections, performance impacts, and safety considerations from automotive experts with decades of experience in tire engineering.
Get industry-standard tire measurements with real-time calculations using automotive engineering formulas
Calculate exact speedometer errors and actual vs indicated speeds for accurate odometer readings
Understand fuel economy impacts, acceleration changes, and ground clearance modifications
Ensure tire changes meet DOT standards and vehicle manufacturer specifications
Learn how to read tire sizes like a professional tire technician. Master the standardized tire sizing system used globally by manufacturers and understand what each number means for your vehicle's performance.
P = Passenger car tire, LT = Light truck, ST = Special trailer, T = Temporary spare
European tires often omit this prefix. Missing prefix typically indicates metric sizing standard.
Tire width measured from sidewall to sidewall when properly inflated and mounted. Common widths range from 125mm to 335mm.
Sidewall height as percentage of section width. Lower numbers = shorter sidewall = better handling.
R = Radial (99% of modern tires), D = Diagonal bias (obsolete), B = Belted bias (rare)
Radial construction provides better fuel economy, longer tread life, and improved handling compared to bias-ply tires.
Wheel diameter in inches (13-26 typical range). Must match your wheel size exactly for proper fitment.
Larger wheels allow for larger brakes but reduce sidewall cushioning. Consider ride comfort vs performance trade-offs.
Maximum weight capacity per tire. Load index 102 = 1,874 lbs capacity.
Maximum sustained speed capability. H rating = 130 mph.
Sidewall Height = (Section Width × Aspect Ratio) ÷ 100Example: 225/65R17 = (225 × 65) ÷ 100 = 146.25mm sidewall
Overall Diameter = (Rim Diameter × 25.4) + (2 × Sidewall Height)Example: 225/65R17 = (17 × 25.4) + (2 × 146.25) = 724.3mm
Circumference = π × Overall Diameter Revolutions per mile = 1,609,344mm ÷ CircumferenceMaster the art of plus sizing and tire conversion. Learn how to safely upgrade wheel sizes while maintaining proper overall diameter for optimal vehicle performance and safety compliance.
Increase wheel diameter by 1 inch, decrease sidewall to maintain overall diameter.
Increase wheel diameter by 2 inches, significantly reduce sidewall height.
Maximum upgrade: 3-inch wheel increase with ultra-low profile tires.
Understand how tire size changes affect speedometer accuracy, odometer readings, and legal compliance. Learn professional calibration techniques used by automotive technicians.
Vehicle speedometers measure wheel rotations per unit time, then calculate speed based on tire circumference. Changing tire size changes this circumference calculation.
Larger tires cause odometer to under-report mileage; smaller tires over-report mileage.
Method 1: Use GPS speedometer apps for real-time verification
Method 2: Mile marker test on highway (time between markers)
Method 3: Professional speed testing equipment
Accuracy: GPS typically accurate within 0.1 mph
Conservative Change (±1%)
Moderate Change (±3%)
Significant Change (>3%)
Understand how tire size changes affect every aspect of vehicle performance, from fuel economy to handling dynamics. Make informed decisions based on automotive engineering principles and real-world testing data.
Conservative Estimates:
Acceleration Impact:
Braking Performance:
Ensure your tire modifications meet DOT safety standards, vehicle manufacturer specifications, and legal requirements. Understand liability implications and insurance coverage considerations for modified tire configurations.
Expert answers to the most common tire size calculator questions
Generally not recommended for most vehicles. Different sizes can cause handling issues, differential damage, and traction control problems. Some high-performance vehicles come with staggered setups from factory, but these are specifically engineered. Always consult your vehicle manual or tire professional.
DOT allows up to 5% speedometer error, but most professionals recommend staying within 3% for optimal performance and legal compliance. Our calculator shows exact percentages to help you stay within safe limits. Consider that police radar shows actual speed, not your speedometer reading.
Larger wheels with lower-profile tires can improve handling and braking, but may reduce ride comfort and fuel economy. The optimal size depends on your priorities: comfort vs performance. Plus 1 sizing typically offers the best balance, while Plus 2 or 3 significantly favors performance over comfort.
For changes within 3% of original diameter, recalibration usually isn't necessary. Larger changes may benefit from speedometer recalibration, especially if you frequently drive at highway speeds. Modern vehicles may also need TPMS (Tire Pressure Monitoring System) reprogramming for different tire sizes.
Reasonable tire size changes typically don't void warranties, but extreme modifications might affect coverage for related components. Document that any problems aren't modification-related. Keep original wheels and tires if you need warranty service, and consult your dealer before making significant changes.
Always match or exceed the original load index. Find your vehicle's weight in the owner's manual or door placard, divide by 4 tires, add 20% safety margin. Our calculator helps verify that new sizes meet capacity requirements. For towing or heavy loads, consider LT (Light Truck) tires with higher load ratings.
P-metric tires (P225/65R17) are designed for passenger cars with optimized comfort and fuel economy. LT tires (LT225/75R17) are built for light trucks with higher load capacity and durability. LT tires typically have stiffer sidewalls and can handle more weight, but may provide a harsher ride on passenger cars.
Our calculator uses industry-standard formulas certified by tire engineers and matches results from professional automotive software. Calculations are accurate to within 0.1mm for dimensions and 0.01% for percentages. Real-world variations may occur due to tire manufacturing tolerances, inflation pressure, and tread wear patterns.
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Industry-standard formulas certified by automotive engineers with real-time calculations
Comprehensive Analysis
Complete performance impact analysis including safety warnings and compliance checks
Visual Comparisons
Professional-grade tire visualizations with proportional accuracy and detailed measurements