The World Rally Car specification emerged from the FIA's desire to allow manufacturers greater freedom to develop competitive and visually dramatic cars without requiring them to produce homologation specials in large quantities. Unlike Group A, which required the base model to be produced in runs of at least 2,500 and demanded the road car carry features relevant to the competition car, the World Rally Car regulations allowed manufacturers to base their entries on common volume models without any direct mechanical relationship between road car and race car. This enabled entries based on the Peugeot 206, Citroën Xsara, and Škoda Fabia, none of which had turbocharged petrol engines or four-wheel drive in their production forms.
Under the original specification, World Rally Cars were required to be built upon a production car with a minimum production run of 2,500 units. Permitted modifications included increasing engine displacement up to 2.0 litres, adding forced induction including anti-lag systems, installing four-wheel drive, fitting a sequential gearbox, modifying suspension layout and attachment points, applying aerodynamic body modifications, and reducing weight to a minimum of 1,230 kg. Maximum width was set at 1,770 mm with front and rear tracks not to exceed 1,550 mm.
To limit power output, all forced induction cars were fitted with a 34 mm diameter air restrictor before the turbocharger inlet, restricting airflow to approximately 10 cubic metres per minute. The intent was to hold power below 220 kW (300 hp), though some engines were believed to produce 330 to 340 hp. Development focus shifted toward producing a very wide power band rather than chasing peak figures, with power outputs above 220 kW typically available from 3,000 rpm all the way to the 7,500 rpm maximum.
By 2004, leading teams had developed cars with ABS, electronic clutch control, paddle-shift transmissions, traction control, three active differentials, GPS-linked ride height control, electronic dampers, and active suspension. From 2006, new regulations required mechanical front and rear differentials with only the central differential remaining active, and banned active suspension and water injection as cost-control measures. Maximum width was increased from 1,770 mm to 1,800 mm from 2005.
From 2011, World Rally Car regulations were significantly revised and became more restrictive. The new rules derived from the Super 2000 specification with an added aerodynamic kit. Cars could be based on smaller models, with the minimum 4-metre length requirement removed. Engines were limited to 1,600 cc direct injection turbocharged units with a 33 mm air restrictor and a maximum boost pressure of 2.5 bar absolute, limiting torque to approximately 400 Nm. Exotic materials including titanium, magnesium, ceramics, and composites were forbidden unless present in the standard production model.
The three-differential arrangement of the previous era was reduced to two differentials, with no central differential, and a mechanical clutch to disconnect the rear axle during handbrake use. Paddle-shift gear changes were banned, requiring a mechanical linkage, though paddle-shifts were re-permitted from 2015. Minimum weight was set at 1,200 kg empty and 1,350 kg with driver and co-driver, rising to 1,360 kg from 2013.
The 2017 regulations retained the 1.6-litre turbocharged engine but increased the turbo restrictor diameter from 33 mm to 36 mm, raising power output from 230 kW (310 hp) to 280 kW (380 hp). Minimum empty vehicle weight was reduced by 10 kg, while the combined weight with crew and spare wheel remained at 1,360 kg. Manufacturers were given substantially more aerodynamic freedom, including large brake cooling ducts integrated into enlarged wheel arch fairings. Electronically controlled active centre differentials were reintroduced, while front and rear differentials remained mechanical.
Cars built to the 2011 specification were permitted to compete in 2017, but the new 2017 World Rally Cars were restricted to manufacturers' teams only, preventing privateer entries.
The World Rally Car specification governed 25 seasons of the WRC manufacturers' championship and produced some of the most recognisable names in rallying history. It was superseded by Group Rally1 from 2022, which introduced hybrid power units and stricter cost controls through a greater use of standardised components.