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Free Tire Size Calculator - Dimensions Made Easy

Calculate tire dimensions, compare sizes, and understand tire specifications. Find equivalent sizes and check speedometer accuracy for tire changes.

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Calculate Tire Size

Quick Answer

Tire 225/55R17: 225mm wide, 55% aspect ratio, 17" wheel, ~26.7" total diameter. 3% diameter change = 3% speedometer error.

Key Facts about Tire Size Calculator:

  • First number = width in mm
  • Second number = aspect ratio %
  • R = radial construction
  • Last number = wheel diameter (inches)
  • ±3% diameter = ±3% speedometer error

Why Use Our Tire Size Calculator?

Complete tire calculations:

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Size Decoder

Understand tire numbers.

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Dimensions

Width, height, diameter.

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Comparison

Compare two sizes.

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Speedometer

Check accuracy impact.

Instant Results

Get specs immediately.

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100% Private

Your data stays private.

How to Tire Size Calculator in 3 Easy Steps

Calculate tire size:

1

Enter Size

Tire code like 225/55R17.

2

View Specs

See all dimensions.

3

Compare

Optional second size.

Know Your Tires

Decode any tire size

Compare alternatives

Check speedometer impact

Ensure proper fitment

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Tire Expert
All sizes decoded

Common Use Cases for Tire Size Calculator

Perfect for:

Tire Shopping

Compare tire options.

Compare Sizes

Upgrades

Check fitment.

Check Fitment

Speedometer

Calculate error.

Check Error

Frequently Asked Questions

Everything you need to know about our tire size calculator

What do tire numbers mean?

Width/Aspect Ratio + Construction + Wheel Diameter (225/55R17)

225/55R17: 225mm width, 55% aspect ratio (sidewall is 55% of width), R=radial, 17" wheel diameter. Overall diameter ≈ 26.7 inches.

How do I calculate tire diameter?

Wheel diameter + (2 × width × aspect ratio)

Diameter = wheel diameter + (2 × sidewall height). Sidewall = width × aspect ratio. For 225/55R17: sidewall = 225×0.55 = 123.75mm, diameter = 17" + 2(4.87") = 26.74".

How much will different tires affect my speedometer?

Larger tires: actual speed > displayed; smaller: actual < displayed

Speedometer reads based on tire revolutions. Larger tires = actual speed is higher than displayed. 3% larger tire means 60 mph displayed = 61.8 mph actual.

Still have questions? Try the tool yourself!

Calculate Tire Size

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