Having recently purchased GTR, I wanted to know a bit about the FIA-GT
technical specifications. Namely, whether or not ABS and Trac-control were
used in the series. I sent an email to FIA and this was their response &
they offerred tecnical regulations relevant to GTR:

Thanks for your email. I hope you enjoy the game - many of our drivers
have
tried it out, and they all agreed that it was incredibly realistic.
Some of
them were using the simulator to practice some of the circuits, and
were
very impressed...

The full technical regulations can be found on the FIA's web site,
http://www.fia.com/sport/Regulations/gtregs.html

For a brief summary of the technical regulations for 2003/2004 (ie
relevant
to the GTR game) :

Ø Vehicle type eligibility:
Vehicles are eligible in two different classes: GT and N-GT. For a
vehicle
to be eligible, it must be a car homologated by the FIA (GT and N-GT)
or a
car from the list of acceptable cars drawn up by the FIA (N-GT).
Ø Electronic system:
Any automatic or electronic chassis control system or function is
forbidden
even if it is fitted on the original car. This includes anti-lock
braking
system, traction control, damper, suspension or ride height adjustment,
power braking, four-wheel steering, movable ballast in both categories
as
well as automatic or semi-automatic transmissions, power-driven
clutches,
electronically or automatically adjusted final drive differential
systems in
the GT category. Semi-automatic or automatic gearboxes and
differentials
with electronic, pneumatic or hydraulic slip control and closed-loop
electronically controlled system are prohibited, unless they are fitted
on
the series vehicle homologated by the FIA or the list of acceptable
cars
drawn up by the FIA in the N-GT class. A simple open-loop electrical
switch
activated by the driver acting on a system is not considered to be an
electronic control. Power steering may be employed as long as it is a
simple
system, without programmable control.
Ø Bodywork dimensions:
All bodywork dimensions and shape must remain original with the
exception of
alterations permitted under Article 3.6 (strengthening of the chassis
and
bodywork, rear wing, bodywork width, air inlets, etc) and those
required by
Article 3.51 (Between the front and rear wheel centre lines, all
bodywork
visible from directly beneath the car, with the exception of wheel
arches
and exhaust tunnels, must lie on one plane. This plane, called Flat
Bottom
or Reference Surface, must be a uniform, solid, hard, rigid (no degree
of
freedom in relation to the body/chassis unit), impervious surface,
under all
circumstances).
Ø Minimum weight: The weight of the car must not be less than 1100 kg.
Ø Engine: The make and type of engine used must remain original.
Ø GT: The position of the engine is free provided the location and
orientation remain original. The interior dimensions of the cockpit
must
remain original if the engine is re-positioned.
Ø N-GT: Its location, position and orientation, but replacing the
original
mountings to the chassis is allowed.
Ø Fuel capacity: the maximum amount of fuel, which may be carried on
board,
is 100 litres.
Ø Transmission: The transmission system is free.
Ø Brakes: The brake discs must be made from ferrous material. The use
of
titanium is authorised for the brake pistons. Any anti-lock braking
function
and any power braking function are forbidden.
Ø Complete wheels dimensions:
Maximum width: GT: 14 inches
N-GT: 12 inches for a weight < 1300 kg
14 inches for a weight >= 1300 kg
Ø Maximum diameter: 28 inches
Ø The maximum authorised diameter of the rims is 18''