CalKit

Tire Size Calculator

Compare tire sizes and calculate diameter differences.

타이어 1 (기준)

mm
%
인치

타이어 2 (비교)

mm
%
인치
직경 차이
10.9 mm (1.72%)

속도계 오차: 1.72%

타이어 1 상세

규격225/45R17
사이드월 높이101.3 mm
전체 직경634.3 mm
둘레1992.7 mm

타이어 2 상세

규격235/40R18
사이드월 높이94.0 mm
전체 직경645.2 mm
둘레2027.0 mm

비교 결과

직경 차이10.9 mm
직경 차이율1.72%
둘레 차이34.2 mm
속도계 오차1.72%

Overview

The Tire Size Calculator converts tire specifications (e.g., 225/45R17) into overall diameter, width, and sidewall height. It compares two sizes side by side, showing diameter difference and speedometer error to help you choose compatible replacement tires.

Formula

Overall Diameter (mm) = (Section Width x Aspect Ratio / 100 x 2) + (Rim Diameter x 25.4). Example: 225/45R17 → (225 x 0.45 x 2) + (17 x 25.4) = 202.5 + 431.8 = 634.3 mm.

How to Use

  1. 1Enter your current tire size (e.g., 225/45R17).
  2. 2Enter the tire size you want to compare.
  3. 3Click 'Calculate' to see diameter, circumference, and speedometer error comparison.

Tips

  • ✔Choose a replacement size within ±3% overall diameter to minimize speedometer error and maintain ride quality.
  • ✔Wider tires improve grip but may reduce fuel economy.
  • ✔When upsizing the rim (plus-sizing), reduce the aspect ratio to keep the overall diameter similar.
  • ✔Korean road law requires a minimum tread depth of 1.6 mm.
  • ✔Check the DOT date code on the sidewall — consider replacing tires older than 5 years.

FAQ

Q. What do the numbers in 225/45R17 mean?

225 is the section width in mm, 45 is the aspect ratio (sidewall height as a % of width), R means radial construction, and 17 is the rim diameter in inches.

Q. What are the pros and cons of plus-sizing?

Pros include better aesthetics and improved cornering. Cons include a harsher ride, reduced fuel economy, and potentially more road noise.

Q. Does changing the tire diameter affect the speedometer?

Yes. A larger diameter makes the speedometer read lower than actual speed, and a smaller diameter makes it read higher. Stay within ±3% to keep the error acceptable.

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