Tire Size Calculator
Compare two tire sizes: sidewall height, overall diameter, width, circumference, speedometer error and ground clearance change. Enter sizes like 225/65R17. Example: replacing 225/65R17 with 235/60R18 changes diameter by about 2 percent (0.58 inches).
Show steps
How to use the Tire Size Calculator
- Type your current tire size from the sidewall, for example 225/65R17.
- Type the new size you are considering.
- Enter the speed shown on your speedometer.
- Press Calculate to compare diameter, width, sidewall and the real speed.
Formula and method
A tire size such as 225/65R17 means 225 mm wide, a sidewall 65% as tall as the width, and a 17 inch rim. Sidewall height = width x aspect ratio. Overall diameter = rim diameter + 2 x sidewall. A larger diameter makes the speedometer read low and a smaller one makes it read high.
Worked example: 225/65R17 vs 235/60R18
| Measure | 225/65R17 | 235/60R18 |
|---|---|---|
| Width | 225 mm (8.86 in) | 235 mm (9.25 in) |
| Sidewall | 146.25 mm (5.76 in) | 141 mm (5.55 in) |
| Overall diameter | 28.52 in | 29.10 in |
| Difference | +0.58 in (+2.0%) | |
How to read a tire size
| Part | Example | Meaning |
|---|---|---|
| Width | 225 | Tread width in millimeters |
| Aspect ratio | 65 | Sidewall height as a percent of width |
| Construction | R | Radial |
| Rim diameter | 17 | Wheel size in inches |
| Load index and speed rating | 98H | Maximum load and speed capability |
Plus sizing: bigger wheel, same tire diameter
When you move to a larger rim, you lower the aspect ratio so the overall diameter stays within about 3% of the original. That keeps the speedometer, gearing and ABS accurate while giving a sportier look and sharper handling at the cost of a firmer ride.
Frequently asked questions
How do I read a tire size?
225/65R17 means 225 mm wide, a sidewall that is 65% of the width, a radial tire, for a 17 inch wheel.
How much can I change my tire diameter?
Stay within about 3% of the original unless your vehicle maker says otherwise, to keep the speedometer, ABS and gearing accurate.
How do bigger tires affect my speedometer?
A larger diameter means the wheel covers more ground per revolution, so you travel faster than the speedometer shows.
Will wider tires fit my wheels?
Each tire has an approved rim width range. Check the tire maker’s chart and clearance in the wheel well.
What is a plus size tire?
A larger wheel with a lower-profile tire so the overall diameter stays about the same.
Where is my tire size?
On the sidewall of the tire and on the sticker inside the driver door jamb.
Sources
Related calculators
Related to This Article
More math articles
- The Best Grade 6 ELA Practice Tests for Hawaii Students
- Smarter Balanced Grade 8 Math Worksheets: 72 Free Printable PDFs
- Homeostasis, Enzymes, and Nutrition
- 8th Grade Math Worksheets: Free Printable PDFs by Topic
- The Ultimate Algebra 1 Course (+FREE Worksheets)
- The Ultimate AP Calculus BC Course
- How to Unveil the Mysteries of Parametric Equations and Their Graphs
- Words for Quantity, Time, Description, and Place
- How to Become a Better Math Problem Solver & Still Have Steady Nerves?
- 10 Most Common 7th Grade MAP Math Questions
What people say about "Tire Size Calculator: Compare Tire Sizes & Speedometer Error"?
No one replied yet.