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.
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 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. 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.
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.
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.
The TR4 was originally fitted with 15 x 4.5" disc wheels. Optional 48-lace wire wheels could be ordered painted the same colour as the car's bodywork (rare), stove-enamelled (matte silver with chrome spinners, most common) or in matte or polished chrome finishes (originally rare, but now more commonly fitted). The most typical tyres originally fitted were 590-15 cross ply or optional radial tyres.