Buses are often classified as being either 'light' or 'heavy'. The majority of Bristol types fall into the 'heavy' classification.  Although all the Bristol chassis are very similar in construction, they have generally been designed specifically for the type of body that they were intended to receive; thus though there was a strong family resemblance between the K and the L types, the K was specifically a double-deck chassis, the L a single-deck one.   The the typical Bristol chassis is formed from deep steel pressings a quarter of an inch thick.  Corrosion problems are rare, as is chassis distortion due to accident damage.  As a friend of mine put it, when looking at some parts removed from my own bus for reconditioning, 'that's GWR engineering, that is!'.  An interesting comment given the association between the Tilling bus group (to which Bristol belonged) and the main-line railways in the 1930s.

Bristol did manufacture some light-weight vehicles, in the 1950s the LS ('light saloon') type, the SC (small capacity') and in the '60s the SU ('short underfloor') and the LH ('light-weight Horizontal' ), the latter two indicating the position of their engines in the type code.  The SU and the SC departed from normal Bristol practice in that some running gear was bought in, notably axles from Bedford and Austin and gearboxes from David Brown.

The railway connection continued in the 1950s when, like all the Tilling transport companies, the Bristol came under the aegis of the British Transport Commission.  This led to the building of two Bristol/ECW railbuses which had useful lives on the Scottish Region of British Railways.

The Lodekka was an innovation for which the railways were largely responsible;  the number of low-clearance railway bridges that had been constructed during the period in which the railways were being developed meant that uncomfortable 'low bridge' double-deck bodies had been constructed with an upper deck with four seats in a row and a side gangway with limited headroom.  These were very unpopular with the travelling public so, the Lodekka addressed this issue by a clever design incorporating some ideas developed by the LGOC in the 1920s.  The Lodekka's running gear was kept  low down and to one side in the chassis, thus allowing the lower deck gangway to be lower. The use of a patented drop-centre rear axle kept the gangway low between the wheels. This in turn led to an overall reduction in height comparable with a standard 'low bridge' model.   The Lodekka, technically sophisticated for it's time,  proved to be  an excellent vehicle.  Although never sold on the open market, many still exist either in preservation or in use all around the world.

From the mid-1930s on Bristol buses have been powered by diesel engines, either the ubiquitous 4, 5 or 6-cylinder light-weight Gardner or a 6-cylinder power plant of Bristol's own manufacture.  Experiments with engine positioning in buses had been carried out since the late 1920s, there being various arguments in favour of not having the engine in front alongside the driver.  The Bristol, however, retained its engine in the traditional position until 1949 when in line with trends in the rest of the industry Bristol introduced the LS model with its engine mounted amidships.  In 1962 the RE ('Rear Engine') single-deck chassis was introduced and arguably became the UK's most successful chassis of this type; starting life with a traditional Bristol synchromesh gearbox it soon gained a semi-automatic epicyclic gearbox manufactured under licence from Wilson.  At last provincial Bristol drivers acquired some of the luxury that London Transport drivers had enjoyed for many years!  In retrospect it seems this modification was probably brought about as a result of a change in circumstances for Bristol Commercial Vehicles.  This occurred  in 1965, when Leyland took a substantial share in the company, Bristol was once again allowed to sell its vehicles on the open market after being restricted to government-owned companies from 1950.  

In 1966 the VR ('Vertical Rear') double deck chassis was introduced and although suffering from some controversy in its early years, the VR went on to become the last 'pure' Bristol design manufactured by Bristol Commercial Vehicles.  The VR was the standard double-decker for the National Bus Company until the introduction of the Leyland B45 Olympian (initially built at Bristol then later at Workington)  in 1981.  The VR, Lodekka and RE were all offered with Leyland diesel engines later in their production life.

On the following page are some views of the different vehicles produced by Bristol over the years.