Micro Tools
Advertisement

Tire Size Comparison

Compare two tire sizes side by side: diameter, circumference, revolutions per mile and speedometer error, with a visual.

Tire comparison

Enter both tire sizes, e.g. 225/45R17. Results update live.

/
R
/
R
Tire 1
Tire 2
Diameter difference
-

Enter both tire sizes to compare.

Advertisement

How tire diameter is calculated

Overall diameter is the rim diameter plus twice the sidewall height. Sidewall height is the section width times the aspect ratio as a percent, converted from millimeters to inches. A 225/45R17 therefore measures 17 + 2 x (225 x 0.45 / 25.4) = 24.97 inches.

Why diameter changes your speedometer

Your speedometer assumes the factory tire circumference. A larger tire covers more ground per revolution, so the car travels faster than indicated; a smaller tire does the opposite. Staying within 3 percent of the original diameter keeps the error small.

Related tools

Mortgage calculatorMonthly cost with taxes, insurance, PMI and payoff schedule. Loan calculatorMonthly payment and interest for auto and personal loans. Compound interestSee how savings grow with compound interest.

Tire Size Compare FAQs

What does 225/45R17 mean?
225 is the width in millimeters, 45 is the sidewall height as a percentage of the width, R means radial construction, and 17 is the rim diameter in inches.
How much bigger tire can I fit?
Stay within 3 percent of the original overall diameter to avoid speedometer, gearing and clearance problems. The calculator shows the exact percentage change.
Will bigger tires make my speedometer wrong?
Yes. Larger diameter tires make the speedometer read low, so you drive faster than shown. The calculator tells you your true speed at an indicated 60 mph.
Do wider tires affect fuel economy?
Usually yes, slightly. Wider tires have more rolling resistance and aerodynamic drag, which can cost a few percent in fuel economy.
What are revolutions per mile used for?
Tire shops and gear calculators use revs per mile to match replacement tires and to recalibrate speedometers and gearing after a size change.
Advertisement