The Triumph TR3 is a British sports car produced between 1955 and 1962 by the Standard-Triumph Motor Company of Coventry, England.

The stock car is powered by the Standard wet liner inline four, a 1,991 cc (121.5 cu in) straight-four OHV engine initially producing 95 bhp (71 kW; 96 PS), an increase of 5 hp over the TR2 thanks to larger SU-H6 carburettors. This was later increased to 100 bhp at 5000 rpmby the addition of a “high port” cylinder head and enlarged manifold. The four-speed manual gearbox could be supplemented by an overdrive unit on the top three ratios, electrically operated and controlled by a switch on the dashboard. In 1956, the front brakes were changed from drums to discs, a first for a British series production car.

The suspension is by double A-arms, manganese bronze trunnion, coil springs and tube shocks at the front, optional anti-roll bar, and with worm and peg steering. Unlike MGs of the same period, the steering mechanism and linkage have considerable play and friction, which increase with wear.

The rear is conventional leaf springs, with solid axle and lever arm dampers, except that the (box) frame rails are slung under the axle. The wheels are 15 inches in diameter and 4.5 inches wide (increased from 4 inches after the first few TR2s).

Under most conditions the car is very responsive and forgiving, but it has some handling issues. The chassis, which is shared by the TR2, TR3, TR3A and TR4 has limited wheel travel. As a result, on very hard cornering, the inside rear wheel can lift, causing sudden over-steer due to the increased load on the outside rear tire. This is particularly true with radial tires; the original TR2/3/3A suspension was built for crossply tires. The wheel lifting is more sudden than that of other cars, because it is caused by coming to the end of the suspension travel while there is still load on the tire, so the load on the other (outside) rear wheel is a discontinuous function of cornering load, rather than just changing slope.

The TR3 is a true roadster, designed for sunny weather but with removable rain protection. It has a convertible hood (US top) that snaps on and off and removable side curtains, allowing very low doors with padding for the driver’s arm to rest on. There are holes in the floor, with rubber plugs, so that the originally supplied jack might be used from inside the car, as did the Jaguar XK120. The optional heater is poor, and the shut-off valve is under the bonnet (US hood). There is room for a third person or child sitting sideways behind the seats, but no accommodation for them.