Advanced features included the first use of adjustable fascia ventilation in a production car and the option of a unique hard top that consisted of a fixed glass rear window 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 5 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. However, dealers had concerns buyers might not fully appreciate the new amenities so a special short run of TR3A (commonly called TR3"B") were produced in 1961 and '62.
Despite dealer concerns, the TR4 proved very successful and continued the rugged, hairy-chested image that the previous TRs had enjoyed. It became a celebrated rally car in Europe and the UK during early to mid-sixties. In America, the TR4 also saw a number of racing successes, even winning an SCCA class championship as late as 1991. In Australia the TR4 was a common site at hill-climb events and various club rallies and circuit racing events.
Some cars were fitted with vane-type superchargers, as the three main bearing engine was liable to crankshaft failure if revved beyong 6,500 rpm. Superchargers allowed a TR4 to produce much more horse-power and torque at relatively modest revolutions. The standard engine produced 105 bhp (78 kW) SAE but supercharged and otherwise performance tuned a 2.2 litre version could produce in excess of 200 bhp (150 kW) at the flywheel. It should be noted that 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 (ie below or above 2 litres for example).
TR4 were originally fitted with 15x4.5" disk wheels. Optional 48 lace wire wheels could be ordered painted the same colour as the car's bodywork (rare), stove-enameled (matte silver with chrome spinners, most common) or in matte or polished chrome finishes (originally rare, but now more commonly fitted). The most typical tyre originally fitted was 165x15 bias ply. In the US at one point, American Racing alloy (magnesium and aluminium) wheels were offered as an option, in 15x5.5" or 15x6" size. Tyres were a problem for original owners who opted for 48 spoke wire wheels, as the correct size radial ply tyre for the factory rims was 175x15, an odd sized tyre at the time that was only available from Michelin at considerable expense. The much more common 185x15 radials were too wide to be fitted safely. As a result, many owners had new and wider rims fitted and their wheels re-laced.
In 1965, the Triumph TR4A with IRS or independent rear suspension superseded the TR4. Apart from the rear suspension, which required a redesigned frame and a number of small styling changes and refinements, the two models appear nearly identical. In fact, an estimated 25% of TR4A were not equipped with IRS, but instead reverted to a live axle design similar to the TR4.Source: Wikipedia.