The Triumph TR4 is a sports car produced by the Triumph Motor Company from 1961 to 1965. As the successor to the TR3A, the car was based on the chassis and drivetrain of the previous TR sports cars, but with a modern body designed by Michelotti.
In spite of its modern styling, a total of only 40,253 cars were built during its 5-year production run. In comparison, the TR2 sold 8,635 units in its 3-year run from 1953–1955; 74,800 TR3s in an 8-year run from 1955 to 1962; 94,500 TR6s in an 9-year run from 1968–1976 and 111,500 TR7s over a 7-year run from 1975–1981.
Styling and coachwork
Code named "Zest" during development, the new TR4 body style did away with the cutaway door design of the previous TRs to allow for wind-down (roll-up) windows in place of less convenient side-curtains. The angular rear allowed a boot (trunk) with considerable capacity for a sports car.
Advanced features included the use of adjustable fascia ventilation, and the option of a unique hard top that consisted of a fixed glass rear window (called a backlight) with an integral rollbar and a detachable, steel centre panel (aluminium for the first 500 units). This was the first such roof system on a production car and preceded by five years the Porsche 911/912 Targa, which has since become a generic name for this style of top.
On the TR4 the rigid roof panel was replaceable with an easily folded and stowed vinyl insert and supporting frame called a "Surrey top". The entire hard top assembly is often mistakenly referred to as a Surrey top. In original factory parts catalogues the rigid top and backlight assembly is listed as the Hard Top kit. The vinyl insert and frame are offered separately as a Surrey top.
Features such as wind-down windows were seen as a necessary step forward to meet competition and achieve good sales in the important US market, where the vast majority of TR4s were eventually sold. Dealers had concerns that buyers might not fully appreciate the new amenities, therefore a special short run of TR3As (commonly called TR3Bs) was produced in 1961 and '62.
As of Q2 2022 there were approximately 953 licensed and 216 SORN TR4s registered with the DVLA.
Engineering
The pushrod Standard inline-four engine, was designed for use by the Ferguson TE20 tractor. The TR4 engine was continued from the earlier TR2/3 models, but the displacement was increased from 1991cc to 2138 cc in the TR4 by increasing bore size. Gradual improvements in the manifolds and cylinder head allowed for some improvements culminating in the TR4A model. The 1991 cc engine became a no-cost option for those cars destined to race in the under-two-litre classes of the day. Some cars were fitted with vane-type superchargers, as the three main bearing engine was prone to crankshaft failure if revved beyond 6,500 rpm; superchargers allowed a TR4 to produce much more horsepower and torque at relatively modest revolutions. The standard engine produced SAE but, supercharged and otherwise performance-tuned, a 2.2-litre I4 version could produce in excess of at the flywheel. The TR4, in common with its predecessors, was fitted with a wet-sleeve engine, so that for competition use the engine's cubic capacity could be changed by swapping the cylinder liners and pistons, allowing a competitor to race under different capacity rules (i.e. below or above 2 litres for example).
Other key improvements over the TR3 included a wider track front and rear, slightly larger standard engine displacement, full synchromesh on all forward gears, and rack and pinion steering. In addition, the optional Laycock de Normanville electrically operated overdrive could now be selected for second and third gears as well as fourth, effectively providing the TR4 with a seven-speed manual close ratio gearbox.