Battle Magazine — March 1997

Many drift drivers nationwide already know Kei Office for its sharp suspension. Now it is releasing the revolutionary ERFOLG (Air Full-K) coilover kit. Its many innovations include: a complete kit for all supported vehicles for under ¥200,000; separate preload and ride-height adjustment; no spring slack or loss of travel; adjustable damping shocks; and pillow-ball mounts on some vehicles. Kei Office spent about four years developing and refining this product. It is primarily designed for grip driving and time attack, but it also works perfectly for drifting. It has already won an Option magazine event and swept first, second, and third at the Tsukuba Grand Champion event. The S13 version was released as a limited run of 250 in December and sold out immediately. Even before driving it, seeing the real thing is exciting.

Spring rates: 4 kgf/mm (initial 2.2 kgf/mm, free length 280 mm, ID 60 mm); 5 kgf/mm (initial 2.6, length 260 mm); 6 kgf/mm (initial 2.7, length 250 mm); 7 kgf/mm (initial 3.1, length 250 mm); 8 kgf/mm (initial 3.4, length 250 mm); 9 kgf/mm (initial 3.9, length 250 mm); 10 kgf/mm (initial 4.4, length 240 mm); 12 kgf/mm (initial 5.0, length 240 mm); 14 kgf/mm (initial 5.7, length 240 mm).

When compressed, it preserves more travel than a conventional cylindrical spring and resists coil bind. When extended, it keeps the tire in contact with the road and improves tracking. With the same spring rate, the larger diameter requires fewer coils and reduces weight—benefits all around. It is suitable for hard driving, and the main spring can handle the load. All released springs have a 60 mm inner diameter, so they fit most coilovers. At ¥18,000 for a pair, the price is excellent. Performance like this at the price of a standard straight-wound spring is welcome. There are nine rates: 4–10 kgf/mm in 1 kg increments, then 12 and 14 kgf/mm, so you can choose the rate you prefer.