You have to go back in history to appreciate the reason for specifying the Gardner engine in the Citybus Tigers.

Citybus was the successor to Belfast Corporation Transport Department which, with few exceptions since the Second World War (ex-LT Daimler CWA6's with AEC engines being the main one), had bought Daimler and Guy chassis all with Gardner units. The Chief Engineer of Citybus since its inception was a municipal transport engineer through and through. This long experience with the Gardner engine and its frugal fuel usage and high mileage reliability was the driving force behind the adoption of this engine for urban application rather than the Leyland TL11 which was the Ulsterbus standard. Hard one fuel economy was not going to be readily sacrificed even if the Gardner was more expensive! Unfortunately to squeeze the much larger Gardner unit into the available space Leyland found it necessary to cut and modify the chassis which was generally felt had a detrimental effect on the smoothness of these particular vehicles. Ulsterbus did take one Gardner example (although with a different engine model) several years earlier which was generally regarded as a better vehicle than the Citybus machines - it has now been preserved in England. The Citybus examples, of which 35 were purchased, differed in several other respects, most notably in being fitted with Taperlite springs (as opposed to air bags of the Ulsterbus vehicles) and low profile tyres to help reduce the entrance step height. This was of course a few years ahead of the general introduction of low-floor vehicles by manufacturers.

Other operators, most notably within the Scottish Bus Group, also specified Tigers with Gardner engines but with the air suspension.

In general it can be said that the Citybus Tigers were probably the least liked of all the vehicles purchased by Citybus and Ulsterbus, a lot of that being down to their lack of speed and noise.