RALT was a manufacturer of single-seater racing cars, founded by ex-Jack Brabham associate Ron Tauranac after he sold out his interest in Brabham to Bernie Ecclestone. Ron and his brother had built some specials in Australia in the 1950s under the RALT name (standing for Ron and Austin Lewis Tauranac). Tauranac won the 1954 NSW Hillclimb Championship in the RALT 500.
As a constructor, Tauranac acquired a reputation for building safe, simple, strong cars that were manufactured to very high standards -- he tended to invest his firm's profits in high-quality machine tools and Ralts acquired an enviable reputation as the best-built "customer" cars of their era.
The early Ralts
Built with the assistance of Tauranac's younger brother, Austin, in Australia. Mk1 Powered by a 1932 pushrod Norton ES2. Tauranac made his own flywheel, connecting rods, cylinders, and so on. The Mk2 was a sports car built by and for Austin, with a Ford 10 engine, Standard 10 gearbox, and Morris 8 rear axle. The Mk3 was purchased from the Hooper brothers when they retired. Tauranac designed a new chassis for it, and the car was primarily driven by Austin. The Mk4 began as a special, using a Vincent-HRD 1,000 cc (61 cu in) V-twin and a de Dion rear suspension. The car took two years to develop in Tauranac’s spare time. After just two events, somebody insisted on buying it, so plans were made for a production run of five. The Mk5 was planned by Austin as a Peugeot-engined car, but abandoned so he could assist Tauranac with the production Mk 4s.
The modern RALTS
The RT2 was a Formula Two car for 1979 with three cars being built for the Toleman team. Later three more cars were built for private owners including one exclusively for the revival of the CanAm series. The Toleman Group built their own (TG280) cars for 1980 based somewhat on the RT2 design and later licensed Lola to build it as the T850. Further-modified Tolemans appeared in F2 as Docking-Spitzleys. Two of the original Toleman RT2 team cars ended up in the Can-Am series. The third one ended up in South Africa where copies called Lants were made. Related cars have appeared in hillclimb and sprint events in the UK as Romans and SPAs.
RT3 was a Formula 3 car derived from the RT2. RT4 was a Formula Atlantic car based on the RT2. Some RT4s did occasionally appear in F2. RT5 was a Formula Super Vee car derived from the RT2 and very similar to the RT3. The RT4 was the choice of car in Australian Formula 1 and Formula Mondial, winning the Australian Grand Prix from 1981-84 (including Alain Prost's win in 1982) and the Australian Drivers' Championship in 1984, 1985 and 1986.
Works F2 cars
RH6 was the start of Ralt's association with Honda in Formula Two (but not Ron Tauranac's - he had been Jack Brabham's partner when Brabham introduced Honda to F2 in the 1960s). The RH6 designation was used for works cars between 1980 and 1984, with the 1980 and 81 cars being a development of the RT2 theme and 1982-4 cars being further developed around a new honeycomb tub.
Formula 3000 cars
RB20 was the marque's first Formula 3000 car, and in keeping with most of the Formula 3000 grid in 1985, it was essentially a further development of the last generation of the RH6, fitted with a Cosworth DFV engine. (The 'B' was for Bridgestone, Ralt's main sponsor)
RT20 was a cheaper, more economical Formula 3000 for 1986, with a traditional aluminium tub - easier to maintain. The works team used John Judd/Honda V8s, but customers used Cosworths. RT21 was a further development for 1987, this time again incorporating honeycomb elements in the monocoque. RT22 (1988) was Ralt's last season as an independent constructor in Formula 3000. The RT22 was its first carbon-fibre Formula 3000, but little success was achieved. RT23 (1991) was designed partly by Tauranac but manufactured under the auspices of the March Group who had bought out the team; there were major chassis problems with this and it was not at all successful. A couple of cars were developed for 1992 as the RT24 (by Simtek), to no avail.
Formula Three Cars
RT3 has a long history - a 1979 ground effect Formula Three car which was enhanced every year until 1984, becoming the dominant car in the formula. RT30 was introduced for the flat-bottom rules coming into effect in 1985. This was notable mainly for being very asymmetric - it had only one sidepod containing a radiator, and a deformable structure panel on the other side. The RT30 was, like many Ralts, developed over several seasons, evolving by the 1985-6 seasons into a highly competitive car, although some teams converted their old RT30s into flat-bottom cars and enjoyed a measure of success with these. 
RT31, the 1987 car, applied some of the honeycomb ideas from the RT21 F3000 car; it was fairly competitive but Gary Brabham's experiments with lowering the engine showed the way ahead. RT32: for the 1988 season, Gary Brabham's modifications were incorporated and a honeycomb/carbon tub was adopted. The RT32 theme saw Ralt through to the end of Ron's time with them, subsequent RT33 (1989)-RT35 (1991) cars essentially being developments of this basic model. The 1992 RT36 was designed by Andy Thorby and lightly revised by Tauranac for 1993 as the RT37. These cars were not particularly successful in Formula Three (in part because many teams switched to Dallara chassis and therefore did not develop them) but the basic monocoque continues to be extremely successful as a hillclimb car nearly fifteen years later. The Ralt 94C was designed by Chris Radage and was not a success.
Later Formula Atlantic variants
RT40 and RT41 were FAtlantic derivatives of the later Formula Three cars; RT40 was the last Ralt with which Ron was involved. Many Champcar World Series and Indy Racing League drivers past and present, honed their skills in these cars, including Jacques Villeneuve, the 1995 Indy 500 winner and 1997 F1 World Champion. After being phased out of the Pro Atlantic series in 1998 in favor of the Swift 008a, the Ralt RT40 and 41s are still being raced competitively (2007) in the Sports Car Club of America, some 13-14 years after the RT40's debut, winning the SCCA Championship as recently as 2003.
Originally equipped for Pro Atlantic racing with a highly tuned variant of Toyota 4A-GE twin cam engine displacing 1.6 litres and developing approximately 250 bhp; several of these chassis have been converted both with bodywork to compete in C Sports Racer (CSR) and with other engine packages such as the twin rotor 13b Mazda, Honda and Cosworth 1600.
Ralt in other hands
Ralt's 1988 Formula 3000 car was proving a challenge to develop; the works drivers' backers (for the first time, Ron was running paying drivers rather than paying his own!) encouraged them to leave the team and not pay up; the company was also suffering from loss of its American markets for RT4s (Swift were upping the stakes dramatically) and RT5s (SuperVee was on its last legs in the USA as a major category). Reynard's aggressive marketing was cutting into the F3000 and F3 markets. Tauranac was looking to sell the company and ultimately ended up selling out to March for just over a million pounds; they had concentrated on high-value bespoke racing cars and allowed their customer cars to atrophy so the merger appeared to be a good move.
The subsequent history of Ralt as part of March is complex, but can be summarised as - operated as March's customer car division for a couple of years, was part of a management buyout when the March Group board decided to divest itself of all its motor racing interests; bought by enthusiasts Andrew Fitton and Steve Ward in 1993. Ron Tauranac left from the firm soon after. Fitton and Ward wound March up, but Ward continued operating Ralt independently - the Ralt name continues, and Ralt F3 cars have occasionally appeared.
Ron Tauranac post-Ralt
Ron has remained involved with various aspects of the sport since departing from Ralt, including racing-school cars for Honda, a Formula Renault car, consulting work for the Arrows formula one team, and continuing his relationship with Honda that goes back to their early Formula Two days as engine supplier to Brabham in the 1960s. RALT Australia was run by New Zealander Graham Watson until his death in 2009. 
- http://www.500race.org/Marques/ralt.htm 500 Race website article
- http://www.f3history.co.uk/Manufacturers/Ralt/ralt.htm F3 History article
- http://www.nmd.com.au/nmd/news/details/7347 NMD Articles. 2009