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Home Page > Miscellaneous > General Tools

Tire Size Calculator

Compare two tire sizes side by side with visual diagrams, speedometer correction, and detailed measurements including diameter, circumference, sidewall height, and revolutions per mile.

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Quick Comparisons:

Plus One: 16" to 17" Plus One: 17" to 18" Plus Two: 16" to 18" Truck: 17" to 18" Same Width Upgrade
Original Tire
225/45R17
New Tire
235/40R18

Embed Tire Size Calculator Widget

About Tire Size Calculator

Welcome to the Tire Size Calculator, a comprehensive tool for comparing tire sizes and understanding how changes affect your vehicle. Whether you are upgrading your wheels, looking for plus-size alternatives, or checking if new tires will fit, this calculator provides visual comparisons, speedometer corrections, and detailed measurements to help you make an informed decision.

What Do Tire Size Numbers Mean?

Tire sizes follow a standardized format like 225/45R17. Here is what each number represents:

How Overall Diameter is Calculated

The overall tire diameter is calculated by adding the rim diameter to twice the sidewall height:

For example, a 225/45R17 tire: sidewall = 225 x 0.45 = 101.25mm, diameter = (2 x 101.25) + (17 x 25.4) = 634.3mm (24.97 inches).

Understanding Plus Sizing

Plus sizing is the practice of increasing wheel diameter while decreasing sidewall height to maintain approximately the same overall tire diameter. This is the most common reason people compare tire sizes.

Plus Sizing Chart

Benefits of Plus Sizing

Trade-offs of Plus Sizing

How Tire Size Affects Your Speedometer

Your vehicle's speedometer is calibrated for the original tire size. When you change tire sizes, the speedometer reading will be affected:

The formula is: Actual Speed = Speedometer Reading x (New Circumference / Original Circumference)

Most manufacturers recommend keeping the overall diameter within 3% of the original to minimize speedometer error and maintain proper vehicle dynamics.

How to Use This Calculator

  1. Enter your original tire size: Select the width, aspect ratio, and rim diameter of your current tires from the dropdown menus.
  2. Enter the new tire size: Select the width, aspect ratio, and rim diameter of the tires you want to compare.
  3. Use quick presets: Click any preset button for common plus-size conversions to instantly populate both fields.
  4. Click Compare: Hit the "Compare Tire Sizes" button to see the full comparison.
  5. Review results: Examine the visual tire comparison, dimension differences, speedometer correction table, and fitment assessment.

Understanding the Results

Visual Tire Comparison

The animated tire diagrams show both tires drawn to proportional scale, making it easy to see the size difference at a glance. The outer ring represents the tire rubber while the inner circle represents the wheel rim.

Dimension Differences

The key metrics show the differences in diameter, width, sidewall height, and ground clearance between the two tire sizes, expressed in both millimeters and inches with percentage changes.

Speedometer Correction Table

The table shows what your actual speed is at various speedometer readings, so you know exactly how much to compensate when driving with different-sized tires.

Fitment Assessment

Tire Size and Fuel Economy

Changing tire size can affect fuel economy in several ways:

Common Tire Size Conversions

Compact Cars

Sedans and SUVs

Trucks and Off-Road

Safety Considerations

Frequently Asked Questions

What do tire size numbers mean?

A tire size like 225/45R17 breaks down as: 225 is the tire width in millimeters, 45 is the aspect ratio (sidewall height as a percentage of width), R means radial construction, and 17 is the wheel rim diameter in inches. The overall tire diameter is calculated from these numbers.

How much tire size difference is acceptable?

Most experts recommend keeping the overall diameter within 3% of the original tire size. Up to 5% may be acceptable but could require adjustments. Differences beyond 5% may cause speedometer errors, ABS issues, and potential rubbing against fender wells.

How does tire size affect my speedometer?

Larger tires cover more ground per revolution, so your speedometer will read slower than your actual speed. Smaller tires do the opposite - your speedometer will read faster than your actual speed. For example, a 3% larger tire means when your speedometer shows 60 mph, you are actually going about 61.8 mph.

Will changing tire size affect fuel economy?

Yes, larger and wider tires generally increase rolling resistance and weight, which can reduce fuel economy by 1-3%. Conversely, the apparent fuel economy on your odometer may seem to improve because the odometer under-counts miles with larger tires. Narrower tires with similar diameter typically have better fuel efficiency.

What is the plus sizing concept for tires?

Plus sizing means increasing the wheel diameter while decreasing the sidewall height to maintain the same overall tire diameter. For example, going from 205/55R16 to 225/45R17 (plus one) keeps roughly the same diameter while giving a wider tread and lower profile for improved handling and appearance.

Additional Resources

Reference this content, page, or tool as:

"Tire Size Calculator" at https://MiniWebtool.com/tire-size-calculator/ from MiniWebtool, https://MiniWebtool.com/

by miniwebtool team. Updated: Mar 24, 2026

Developer API available: Run this tool from your app, automation, or agent with one JSON HTTP request. View API docs

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