Last updated: March 2026
How to Compare Tire Sizes
Comparing tire sizes is essential before upgrading or changing your tires. The most important measurement to compare is the overall diameter, because it directly affects speedometer accuracy, ground clearance, and whether the tire will physically fit your vehicle. A difference of more than 3% in overall diameter is generally not recommended without additional modifications.
Enter your current tire size and the size you're considering. The tool calculates the exact difference in every measurement and shows speedometer error at 60 mph, so you know whether the new size will cause your speedometer to read high or low. The clearance change tells you how much higher or lower the vehicle will sit with the new tires.
What to Look for When Comparing Tires
When switching tire sizes, focus on three key factors. First, check the overall diameter difference — staying within 3% ensures your speedometer remains reasonably accurate and the tires fit without rubbing. Second, look at the width change — wider tires need more fender clearance and may affect steering feel. Third, consider the aspect ratio change — lower aspect ratios mean shorter sidewalls, which improve handling but reduce ride comfort.
The revolutions-per-mile number is useful for understanding fuel economy impact. Fewer revolutions per mile means the tire covers more ground per revolution, which can slightly improve highway fuel economy but may reduce acceleration performance. More revolutions per mile has the opposite effect.
Common Tire Upgrade Scenarios
Plus-sizing means moving to a larger wheel diameter while maintaining a similar overall tire diameter. For example, going from 225/65R17 to 235/55R18 keeps roughly the same overall diameter but gives you a larger wheel and shorter sidewall for improved handling. This is the most common upgrade for appearance and performance.
Upsizing for off-road use typically means increasing the overall diameter for more ground clearance. Truck owners often go from a stock 265/70R17 to a 285/70R17 or larger. The comparison tool shows exactly how much clearance you gain and what the speedometer impact will be, helping you decide if the upgrade is worth the trade-offs.
Frequently Asked Questions
How do I compare two tire sizes?
Enter your current tire size and the new size you're considering. The tool shows side-by-side measurements including overall diameter, width, sidewall height, circumference, and revolutions per mile, plus the exact difference for each measurement.
How much bigger can I go without problems?
Most vehicles can safely accommodate tires within 3% of the original overall diameter. Going beyond that may cause speedometer inaccuracy, rubbing on fenders or suspension components, and changes in handling. Always check your vehicle's owner manual for approved tire sizes.
Will bigger tires affect my gas mileage?
Yes. Larger and wider tires typically increase rolling resistance, which can reduce fuel economy by 1-3%. The heavier weight of larger tires also requires more energy to accelerate. However, the difference is usually modest for changes within the 3% diameter guideline.
How do I know if a tire will fit my car?
Check the overall diameter difference (stay within 3%), the width increase (ensure adequate fender clearance), and the clearance change shown in the comparison. Also verify the wheel diameter matches your rims. When in doubt, consult a tire professional.
Does changing tire size affect my odometer?
Yes. Just like the speedometer, your odometer is calibrated for the original tire size. Larger tires mean fewer revolutions per mile, so your odometer will under-report actual miles driven. A 3% larger tire means your odometer reads about 3% low.