Small car, big idea: the kei standard

The kei class began as a line in the vehicle regulations. Its limits on size and displacement were revised again and again, and each revision changed what engineers could build.

1. 1949

   The kei-jidosha (light automobile) category first appeared in Japanese vehicle regulations in July 1949, with limits of 2.8 m length, 1.0 m width, 2.0 m height, and 150 cc (four-stroke) or 100 cc (two-stroke).

   Source: 軽自動車 — ウィキペディア日本語版
2. 1950

   In July 1950 the kei standard was revised to 300 cc (four-stroke) or 200 cc (two-stroke), with limits of 3.0 m length, 1.3 m width and 2.0 m height.

   Source: 軽自動車 — ウィキペディア日本語版
3. 1951

   In August 1951 the kei standard was re-set under the Road Transport Vehicle Act enforcement regulations at 360 cc (four-stroke) or 240 cc (two-stroke).

   Source: 軽自動車 — ウィキペディア日本語版
4. 1954

   In October 1954 the kei displacement limit was unified at 360 cc for both four-stroke and two-stroke engines (English Wikipedia dates this change to 1955).

   Source: 軽自動車 — ウィキペディア日本語版

Within the 360 cc rules, makers built genuine four-seat cars for households that had never owned one.

1. 1958

   The Subaru 360 went on sale in March 1958 and helped kei cars spread widely among Japanese households.

   Source: 軽自動車 — ウィキペディア日本語版

Emissions and safety pushed the limits outward. Larger dimensions arrived so that kei cars could meet the same collision standards as bigger cars.

1. 1976

   From January 1976 the kei standard was enlarged to 550 cc with a length of 3.2 m and width of 1.4 m (height 2.0 m), a change linked to tightening emission regulations.

   Source: 軽自動車 — ウィキペディア日本語版
2. 1990

   In 1990 the kei standard was revised to 660 cc with a maximum length of 3.3 m (width 1.4 m, height 2.0 m).

   Source: 軽自動車 — ウィキペディア日本語版
3. 1998

   In October 1998 the current kei standard took effect: length 3.4 m, width 1.48 m, height 2.0 m, 660 cc, adopted so that kei cars could meet the same collision-safety standards as larger cars.

   Source: 軽自動車 — ウィキペディア日本語版
4. 04

   Kei cars are subject to a 64 PS maximum power output set by a gentlemen's agreement among Japanese manufacturers rather than by law.

   Source: Kei car — Wikipedia (English)