In the first part, the evolution of the first Triumphs through the TR-3B's was discussed. The Triumphs were redesigned and modernized with the TR-4. The first production TR-4 was built on July 18, 1961. The production of the TR-3B's continued for 18 months after the introduction of the new TR-4 due to their immense popularity.
The more modern body design was a joint effort between Triumph and the German firm Karmann. It was very similar in construction to the TR-3's. The central section and the chassis was of the same design with the dimensions being different. As in the TR-3's, the outer panels belted on to the center section. No aluminum paneling was used.
The driving and handling characteristics were updated with an improved steering system and brakes. The steering was a true rack and pinion type manufactured by Alford & Alder. It resulted in much lighter and more precise steering.
The brakes were the new Girling "B" type split caliper for the front with 11-inch discs for the front and 9-inch drum-type brakes on the rear.
The 2138 cc wet-liner type engine used in the TR-3 was extremely reliable and was mostly unchanged when used in the TR-4 and TR-4A. By increasing the compression ratio the horsepower was increased to 105 h.p.
The TR-4 series was well accepted and its sales continued to set records during the early 1960s. However, it became apparent that in order to continue to maintain its market share in the sports car markets, more performance was needed. Some production changes were made and in 1965 an independent rear suspension (IRS) model was introduced as the TR-4A. p>
The answer to the increased performance was in the new 6-cylinder engine used in the TR-5/250 and later in the TR-6. The first TR-250 was built in July of 1967 and the first TR-5 was built in August of 1967. They were similar cars but had short production runs. In September 1968 the first TR-6 was produced.
This car had a 2498 cc engine producing 150 h.p. Later versions were subject to the U.S. emission restrictions. The car was updated and was quick but was still refined. The car was popular with its relatively comfortable interior, elegant wooden dash, roll-up windows, fully synchromesh transmission, independent rear suspension and its powerful six-cylinder engine. By the end of production in 1976, 91,850 TR-6's had been produced.