P-メトリック/ユーロメトリック変換器

Introduction

The P-Metric/Euro-Metric Converter is an international standard tool that analyzes and cross-converts the subtle but important differences between various tire sizing systems used globally. While P-Metric (primarily US), Euro-Metric, and Japanese JATMA standards may look similar, they have critical differences in how load indices are calculated and how they handle load capacity at different inflation pressures. This tool clarifies these engineering distinctions for safe tire selection.

Expert Analysis & How It Works

The system databases load index tables and pressure correction factors for each standard. For example, while a 205/55R16 might look identical, P-Metric tires are rated for passenger loads, whereas Euro-Metric often handles higher pressures and loads. The converter translates not just physical dimensions (diameter, width) but also max load values (kg/lbs) using each standard's formulas, automatically applying rules like the 9% load reduction required when mounting passenger (P-Metric) tires on SUVs or trucks.

Professional Usage Scenarios

• When buying tires via international shipping or replacing stock tires on an imported vehicle, verify that the different standards don't create issues with load capacity.
• If mounting high-performance European tires on an American pickup truck, use this to precisely compare load index differences between standards to ensure they can safely support the truck's weight.
• For tire professionals explaining the differences between brands from different countries to customers, use this as an authoritative data source for recommending proper inflation pressures.

P-Metric / Euro-Metric コンバーターの使い方

タイヤサイズ、荷重指数、速度記号を選択して、P-metric、Euro-metric、JATMA の各規格間の同等仕様を確認できます。

P-metric（北米規格）は同じ荷重指数でもEuro-metricより耐荷重がやや低くなります。JATMA（日本規格）は表記が異なりますが、物理的寸法は同等です。

3つの規格はすべて同一の物理的タイヤ寸法を持ち、荷重等級のみが規格間で異なります。

The tire size calculator works by applying physical dimensions such as section width, aspect ratio, and rim diameter into precise mathematical formulas. The overall diameter is calculated using the formula 'Rim Diameter + (Section Width x Aspect Ratio/100 x 2)', which then determines the tire's circumference—the distance it travels in one full revolution. These precise calculations allow for accurate predictions of speedometer error, ground clearance changes, and gear ratio impacts down to decimal points. Our system follows international standards to ensure reliable simulations across various tire brands and specifications.

The tire size calculator works by applying physical dimensions such as section width, aspect ratio, and rim diameter into precise mathematical formulas. The overall diameter is calculated using the formula 'Rim Diameter + (Section Width x Aspect Ratio/100 x 2)', which then determines the tire's circumference—the distance it travels in one full revolution. These precise calculations allow for accurate predictions of speedometer error, ground clearance changes, and gear ratio impacts down to decimal points. Our system follows international standards to ensure reliable simulations across various tire brands and specifications.

Key scenarios include finding compatible tire sizes when upgrading to larger rims (plus-sizing), checking diameter differences when switching to narrower tires for better winter traction, and analyzing suspension clearance or gear ratio changes when fitting large-diameter off-road tires. It is also widely used for routine safety checks like verifying actual speed to avoid traffic fines, and calculating load indices for towing RVs or trailers, bridging the gap between daily driving safety and professional vehicle modification.

Key scenarios include finding compatible tire sizes when upgrading to larger rims (plus-sizing), checking diameter differences when switching to narrower tires for better winter traction, and analyzing suspension clearance or gear ratio changes when fitting large-diameter off-road tires. It is also widely used for routine safety checks like verifying actual speed to avoid traffic fines, and calculating load indices for towing RVs or trailers, bridging the gap between daily driving safety and professional vehicle modification.

Q: How much tire diameter difference is acceptable? A: Generally, a difference within ±3% of the original size is recommended; exceeding this can lead to significant speedometer error and affect vehicle control systems like ABS and ESP. Q: Does wider tires decrease fuel economy? A: Yes, a larger contact patch increases rolling resistance, which may slightly lower fuel efficiency, though it improves cornering stability. Q: What is a DOT code? A: It indicates the tire's manufacture date. The first two digits of the last four represent the week, and the last two represent the year. It's safest to replace tires over 10 years old even if tread remains.

Q: How much tire diameter difference is acceptable? A: Generally, a difference within ±3% of the original size is recommended; exceeding this can lead to significant speedometer error and affect vehicle control systems like ABS and ESP. Q: Does wider tires decrease fuel economy? A: Yes, a larger contact patch increases rolling resistance, which may slightly lower fuel efficiency, though it improves cornering stability. Q: What is a DOT code? A: It indicates the tire's manufacture date. The first two digits of the last four represent the week, and the last two represent the year. It's safest to replace tires over 10 years old even if tread remains.