Tire Size Calculator
Compare your stock size with a new one: see the difference in overall diameter and how much your speedometer reading changes. The safe limit is about 3 percent.
Enter both sizes (e.g. 205/55 R16 and 225/45 R17) to compare.
How to read a tire size
A marking like 205/55 R16 means: tire width in millimeters (205), sidewall height as a percent of the width (55 = 55% of 205, about 4.4 in / 113 mm), and rim diameter in inches (16). From these three numbers we work out the overall diameter of the whole wheel.
Can I put a different tire size on my car
Yes, as long as the overall diameter does not change by more than about 3 percent. A bigger change throws off your speedometer, can rub the fender over bumps and can upset ABS and stability control, which read speed from how fast the wheels turn. The calculator above shows right away whether you stay inside the safe range.
Tire size and your speedometer
A larger tire covers more distance per revolution, so you are actually going faster than the gauge shows. A smaller tire does the opposite. That is why it pays to check how much the reading shifts when you change size, and the calculator works it out at 60 mph.
Tires when buying a used car
When you inspect a used car, look at the tire build date (the DOT code) and the tread depth, which we cover in when to replace tires and reading the DOT date. Check that the fitted size matches what the door placard calls for, and see tire pressure and TPMS too. The whole walkaround is easier with the MotoPPI app and its model-specific checklist, see how to inspect a used car.
Frequently asked questions
How much can I change tire size?
Safely up to about 3 percent difference in overall diameter. Beyond that you throw off the speedometer and may run into clearance and fitment issues.
What does 205/55 R16 mean?
Width 205 mm, sidewall 55% of the width, 16-inch rim. From that you calculate the diameter of the whole wheel.