Tire Ratio Calculator
The Tire Ratio Calculator decodes tire size designations and calculates the aspect ratio, sidewall height, overall diameter, and circumference. Compare tire sizes to check speedometer accuracy and ensure proper fitment for your vehicle.
🕐 Recent Calculations
What is Tire Aspect Ratio?
Tire aspect ratio is the ratio of the tire's sidewall height to its section width, expressed as a percentage. In the tire size 225/45R17, '45' is the aspect ratio — the sidewall height is 45% of the 225mm width, equaling 101.25mm. Lower aspect ratios indicate a shorter sidewall (sportier handling), while higher ratios mean a taller sidewall (more comfort).
Tire aspect ratios typically range from 25 (ultra-low profile racing tires) to 80 (off-road and SUV tires). Standard passenger car tires use 50-65. The aspect ratio, combined with wheel diameter, determines the tire's overall diameter and rolling circumference, which affect speedometer calibration.
적용 수학 공식 및 방정식
이 Tire Ratio Calculator는 5가지 핵심 수학 공식을 사용합니다:
1 Sidewall Height ▼
225mm width × 45/100 = 101.25mm sidewall height.
2 Overall Tire Diameter ▼
225/45R17: Diameter = (2 × 101.25) + (17 × 25.4) = 202.5 + 431.8 = 634.3mm = 24.97 inches.
3 Speedometer Error ▼
Going from 634mm to 660mm: Error = (660/634 - 1) × 100 = +4.1%. Speedometer reads slow by 4.1%.
비율 계산기 사용법
이 비율 계산기는 아래의 3단계로 쉽게 사용할 수 있습니다:
수치 입력하기
입력 칸에 알고 있는 비율 값을 입력합니다. 구하려는 미지수 자리의 칸 하나는 비워둡니다.
모드 선택하기
비율 모드(풀기, 간소화, 스케일링)를 선택합니다. 각 모드는 입력한 수치에 맞춰 다른 공식들을 적용합니다.
결과 확인하기
계산하기 버튼을 누릅니다. 결과 화면에 정답과 함께 시각적인 비율 바, 원형 차트, 상세한 단계별 풀이 과정이 출력됩니다.
실제 예제 문제 및 단계별 풀이
비율 계산기를 활용하여 아래 3가지 예제 문제를 단계별로 해결하는 과정입니다:
입력 1 Decode tire size 245/40R18
입력 2 Compare 225/45R17 vs 235/40R18
입력 3 Find aspect ratio for target diameter
자주 묻는 질문 (FAQ)
What does the aspect ratio number mean on a tire? ▼
The aspect ratio is the second number in a tire size (e.g., 45 in 225/45R17). It means the sidewall height is 45% of the tire's width. Lower numbers = shorter sidewall, sportier; higher numbers = taller sidewall, more comfortable.
How does tire aspect ratio affect ride quality? ▼
Higher aspect ratios (55-70) provide more rubber between the road and rim, absorbing bumps better. Lower aspect ratios (35-45) are stiffer, providing sharper handling but transmitting more road imperfections to the cabin.
What aspect ratio is best for performance? ▼
Sport/performance tires typically use 35-45 aspect ratio for maximum grip and responsiveness. Track cars may go as low as 25-30. The tradeoff is harsher ride and increased risk of rim damage from potholes.
Can I change tire aspect ratio without changing wheel size? ▼
Yes, but the overall diameter should stay within 3% of original. Going from 225/55R17 to 225/50R17 lowers the car by about 11mm and makes the speedometer read slightly fast.
How much speedometer error is acceptable? ▼
Most jurisdictions allow 3-5% speedometer variance. Keep tire overall diameter within 3% of the factory size. At 3% oversized, your speedometer shows 60 mph when you're actually going 61.8 mph.