Toyota Celica GT-Four

Lore & Background

The Celica GT-Four came in three generations; the ST165, based on the fourth generation Celica, and manufactured between October 1986 and August 1989; the 'super round' shape ST185 produced from September 1989 to September 1993; and the ST205, built from February 1994 to June 1999. The Celica GT-Four production cars were built at Toyota's Tahara plant in Aichi Prefecture, Japan, and the rally cars were prepared by Toyota Team Europe in Cologne, Germany. The Celica GT-Four ST165 made its World Rally Championship (WRC) debut in the 1988 Tour de Corse, with its first WRC victory coming in the 1989 Rally Australia. The ST185's WRC debut was in the 1992 Rally Monte Carlo, and its first WRC win was in the 1992 Safari Rally, which was one of its four victories in that year. The ST185 was Toyota's most successful rally car for more than two decades until this position was taken by Toyota Yaris WRC, and now the GR Yaris Rally1. The Celica ST185 won the WRC Drivers' Championship in 1992, and the WRC Manufacturers' and Drivers' championships in 1993 and 1994. The ST205 came in late 1994, and became the official rally car in 1995 with one WRC victory before disqualification. It also won the 1996 European Rally Championship. The significance of the Toyota Celica GT-Four in WRC history, previously dominated by European manufacturers, is that it was the first time a Japanese car manufacturer entered the WRC with an AWD turbocharged car, took trophies and won the titles. Since then other Japanese manufacturers have been successful in the WRC. Toyota preceded the Mitsubishi (Lancer Evolution and Galant VR-4) and the Subaru (Legacy and Impreza), but not the Mazda (Mazda 323GT-R & 323GT-X). Toyota later exited the WRC to concentrate their racing efforts in Formula One, but in 2017, 11 years after the Celica was discontinued, Toyota returned to WRC with the Toyota Yaris. Toyota Team Europe (TTE) was also the first to introduce the anti-lag system (ALS) in their Group A ST205 Celica GT-Four rally cars, a technological breakthrough that was later adopted by other teams.

Reader's Guide

The GT-Four system uses hollow splined shafts to provide power to the centre differential first to produce a true 50:50 system. The transmission's driven shaft is geared to the centre differential. Then from the centre differential, the left side gear is connected to the front differential through a short hollow shaft while the right side gear powers the rear through another hollow shaft connected to the transfer pinion. The most important piece is a driveshaft inside both hollow shafts to power the right front wheel completely isolated from the shaft powering the rear wheels. The use of hollow shafts isolates the front power delivery and rear power delivery. They are both powered by the centre differential. This allows for a torque split capable of 100:0 to 0:100 rear bias. However to control power split, Toyota also included a viscous limited-slip coupling joining the left and right side gears of the centre differential to keep it steady at 50:50. In certain conditions such as no grip to the rear tires, one can visibly observe rear bias as only the rear tires will spin before the viscous coupling gives back some torque to the front. Early ST165's (86 and 87 models) used a vacuum-operated actuator to lock the centre differential. This would allow for full range of torque split from 100:0 to 0:100 without the centre locked, and it would be stuck at 50:50 with the centre locked and as such only recommended for off-road use. The GT-Four system is closer to a 4WD system rather than an AWD system because it is powering 4 wheels equally at the same time and there is always a coupling keeping the fronts and rears locked. This is especially true of the early ST165, as the solid-locking centre differential cannot be used on pavement when turning without risking damaging the drivetrain. All three generations of the Celica GT-Four used the same basic system. However, the ST185 RC and ST205 also have a rear Torsen limited-slip differential (LSD) as standard. For the regular ST185, the rear Torsen is standard or optional depending on the year and original market.

Did You Know?

• The Celica GT-Four concept started with a convertible prototype displayed at 1985 Tokyo Motor Show. It was the first car to be officially called Celica GT-Four with the theme 'Open Air 4WD Sport'.
• The ST165 was not sold in North America before 1988 except for seventy-seven special-edition cars sold to commemorate Toyota's IMSA GTO championship win.
• When the Celica GT-Four was launched in the United Kingdom in March 1988 it was the first car sold in the United Kingdom designed to run only on unleaded gasoline.
• The first 21 units of the Celica ST185 were built in December 1988 as prototypes for various tests.