This article is from the Motorsport FAQ, by A H Henry firstname.lastname@example.org with numerous contributions by others.
These are used for touring car championships in Britain, Italy,
Germany, France, Scandinavia, Japan and Australasia.
Cars must have four doors and be longer than 4.2m. 2500 road cars
must be produced within 12 months for the car to be homologated. The
minimum weight is 950kg for front wheel-drive cars and 1050kg for
rear wheel-drive cars.
Engines are 2 litres with a maximum of six cylinders. They can
either come from the homologated car or another model in the
manufacturer's range. If the engine is taken from another model, at
least 2500 engines have to been built in a 12 month period. An
electronic limiter restricts engine revs to 8500 rpm. The gearbox is
free but cannot have more than six ratios. The original layout of the
engine must be retained from the car (ie longitudinal or transverse).
Tyre width is limited to nine inches. At BTCC meetings only six
dry, six wet and six intermediate tyres can be used for the whole of
the meeting. At double header races, where the races are held ten
minutes apart, tyres are free for the second race.