Editing Triumph TR4 (section)

== Development ==
Triumph began planning a successor to the TR3 as early as 1956. At the time, the company was facing a number of challenges. Lack of capital to fund development was partly relieved by the sale of Triumph's tractor division to Massey-Harris of Canada. A long overdue refresh of their small sedans was further complicated by the departure of chief stylist Walter Belgrove over a disagreement with the direction of the redesign.<ref name="krausebook-ch3"/>

After being introduced to [[Giovanni Michelotti]], Triumph managing director Alick Dick invited the Italian designer to produce a [[concept car]] for the British company.<ref name="krausebook-ch3"/> Michelotti responded with the Triumph TR3 Speciale, also called the "TR Dream Car".<ref name="alkureishibook"/>

Built by [[Vignale]] on an unmodified TR3 chassis, Michelotti's TR Dream Car incorporated many styling cues from contemporary American practice, including tailfins, a full width grille, lidded headlamps in the tops of the front wings, and a two-tone paint treatment.<ref name="krausebook-ch3"/><ref name="rlh-history"/> The TR3 Speciale debuted at the [[Geneva International Motor Show]] in March 1957.<ref name="auwm-oct2012"/> Triumph deemed the car too expensive to put into production, but did give the job of designing the new [[Triumph Herald]] to Michelotti.<ref name="pa-prototypes"/><ref name="krausebook-ch3"/>

Later in 1957 Standard-Triumph commissioned Michelotti to develop a serious proposal for a revised TR. A prototype, code-named ''Zest'' and built on a TR3A chassis, was complete by 1958.<ref name="pa-prototypes"/><ref name="auwm-oct2012"/><ref name="rlh-history"/> The ''Zest'' received a full-width body style, with headlamps that were inset from the sides and set high in the grille to stand above the bonnet, which was shaped into cowls over the lamps.

Around this time Triumph's Competitions department was working on a new high-performance engine with the development label ''20X'', later named  [[Triumph Sabrina engine|Sabrina]] after contemporary British actress [[Sabrina (actress)|Norma Ann Sykes]], the 20X is an inline four cylinder engine with [[Overhead camshaft engine#Double overhead camshaft (DOHC)|dual overhead camshafts]], and was expected to develop {{cvt|160|hp|kW|0}}. To accommodate the engine, a chassis was created that widened the track by four inches and extended the wheelbase by six inches over those of the TR3.<ref name="rlh-history"/>

In late 1958 Triumph commissioned Michelotti to create a body for the 20X development chassis. The new shape, named ''Zoom'', was a full-width body, with tall doors having wind-down windows, and headlamps moved to the tops of the front wings. Two prototypes were complete by 1959; one convertible and one coupé with a removable roof panel.<ref name="auwm-oct2012"/><ref name="revington-zoom"/>

The ''Zoom'' body was used for the three Triumph TRS race cars fielded at the [[1960 24 Hours of Le Mans]], which were powered by three 20X DOHC engines.<ref name="auwm-oct2012"/> The cars staged a formation finish, but were unclassified due to having failed to cover their mandatory distance. The cars were revised and entered again in the 1961 race, where they finished ninth, eleventh, and fifteenth overall, and claimed the manufacturer's team prize for Triumph.<ref name="pendine-nov2018"/>

By the middle of 1960, Triumph had two potential TR replacements — ''Zest'' and ''Zoom'' — with a combined program cost of £676,000.<ref name="aro-rtpart2"/> Originally, ''Zest'' had been conceived as the TR3's replacement, while ''Zoom'' was considered for production as an upmarket model. Having seen ''Zoom'', some at Triumph wanted it to become the next TR, but the cost to produce a detuned 20X engine killed the project.<ref name="auwm-oct2012"/><ref name="krausebook-ch3"/>

Ultimately management decided that neither ''Zest'' nor ''Zoom'' adequately addressed the target market, so the final design for the TR4 was based on ''Zest'', but included some features from ''Zoom'', including the wider track and hardtop option.<ref name="aro-rtpart3"/><ref name="auwm-oct2012"/><ref name="krausebook-ch3"/>