Tire sizecalculator.
Compare any two tire sizes to instantly see the overall diameter difference, speedometer error, sidewall change and ground clearance. Keep the diameter within about 3% of stock to stay safe.
Original tire
New tire
How to read a tire size
A size like 225/45R17 means: 225 = tread width in mm, 45 = aspect ratio (sidewall height as a percentage of width), R = radial construction, 17 = wheel diameter in inches.
Why tire size matters
- Speedometer accuracy. A larger diameter makes your speedo read slow — you are going faster than it shows.
- Clearance & rubbing. Too tall or wide can rub fenders or suspension at full lock.
- Ride & handling. A lower aspect ratio means sharper handling and a firmer ride.
- Odometer & gearing. Diameter changes shift your distance readings and effective gearing.
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Questions, answered.
How much tire diameter difference is safe?
Keep overall diameter within about 3% of the original to avoid speedometer error, rubbing and drivetrain stress.
Does a bigger tire make the speedometer wrong?
Yes. A larger-diameter tire makes your speedometer read slower than your true speed because the wheel travels farther per rotation.
What does 225/45R17 mean?
225 mm tread width, 45% aspect ratio (sidewall height), R for radial, and a 17-inch wheel diameter.
Will bigger tires fit my car?
Check clearance at full steering lock and suspension compression. Staying within about 3% of stock diameter usually fits.