Visually similar to the TR4 (also styled by Michelotti), the TR5 roadster sported Triumph's much more powerful 2.5-litre straight-6, fitted with Lucas mechanical fuel-injection and producing 150 bhp (110 kW). Price pressures and tighter emissions standards in the U.S. resulted in a much less powerful carburetted version, the TR250, being sold on the North American market.
At the time, fuel injection was uncommon in road cars. Triumph claimed in their sales brochure that it was the "First British production sports car with petrol injection".
The TR5 was available with the "Surrey Top" hard top, a weather protection system with rigid rear section including the rear window and removable fabric section over the driver and passenger's heads.
A curious feature of the TR5/Lucas petrol injection system was the very frequent occurrence of an intermittent power failure when the fuel tank was no more than a quarter full. In order to provide fresh fuel at the distributor, free from overheating/soak, unused fuel was returned to the tank where it entered very close to the high pressure fuel pump. When the fuel level fell below critical (about 3 gallons), sloshing would cause the pump to pick up a slightly aerated mixture which was sent to the fuel distributor. Unused fuel (still aerated) then passed back to the tank and was discharged close to the pump, a proportion of it being picked up and recycled to the distributor. As this cycle was repeated, gradually the volume of air in the pumped fuel reached a level where it began to affect the running of the engine. Adding as little as one gallon to the tank seemed to cure the problem. The similarly engineered contemporary saloon overcame this problem with a petrol tank specially designed for the fuel injected model. This incorporated an anti-slosh cup to ensure that the fuel outlet remained covered with fuel when the tank level was low.
The fuel-injected engine could propel the TR5 from 0–50 mph (80 km/h) in 6.5 seconds, reaching a top speed of 125 mph (201 km/h). Road tests at the time reported slightly different performance figures:
The TR5 was produced in small numbers when compared with the later TR6, with just 2,947 units produced; the first car was assembled on 29 August 1967 and the last on 19 September 1968. Of these, 1,161 were destined for the UK market, the remainder were left hand drive and were exported to France, Belgium and Germany amongst other countries. In the first quarter of 2011 there were approximately 410 licensed and 74 SORN TR5s registered with the DVLA.
The Triumph TR250 was built during the same period for the North American market. Price pressures and tighter emission regulations resulted in twin Zenith-Stromberg carburettors being fitted instead of the TR5's Lucas fuel injection system. Otherwise it is nearly identical.
The TR250's engine delivered 111 bhp (81 kW), 39 bhp less than the TR5; 0–60 mph (0–97 km/h) acceleration took 10.6 seconds. The TR250 was also available with the Surrey Top system.
In 1968, the TR250 sold in North America for approximately $3,395, with wire wheels a $118 option, overdrive $175, and air conditioning $395.
2,498 cc, inline-six cylinder, 74.7 mm (2.9 in) bore, 95 mm (3.7 in) stroke, 8.5:1 compression ratio, 111 bhp (83 kW; 113 PS) at 4,500 rpm