Miles per gallon

[Mike Wattam <101714.1343@domain.elided>]

Hi David

What you are rhinking of was the introduction in the UK of the "Passenger
car fuel consumption order 1977" which made all vehicle manufacturers quote
fuel consumptions in fixed driving conditions which were;

1.  urban test cycle
2.  constant speed of 56mph (90kph)
3.  optional high speed test at 75mph (120kph)

As the Stag had already dropped out of production, it was never tested or
publicised in this cycle.  However, the other figures published may still
be relevant because compulsory exhaust emissions testing as part of the
MOT, has probably resulted in Stags running very economically.

It has also subsequently been found that the cycle was not truly
representative, as all manufacturers went for ridiculuously high economies
at the 56mph constant speed.  However, for comparison purposes here are a
few similar test results you might be able to work out the Stag figures
from.

                        URBAN   56      75      Triumph*
Stag manual o/d         -       -       -       30.8
MGB-GT Manual o/d               24.1    41.1    34.4    
Dolomite 1850 manual o/d        30.3    46.7    31.6    33.7
Doly Sprint manual o/d  23.4    40.4    31.9    35.3
Doly Sprint Auto                23.1    36.5    27.4
Spitfire 1500 o/d               28.7    52.9    36.3    47.0
TR7 8-valve 5 speed     22.7    37.9    30.7
TR7 8-valve auto                26.2    41.5    29.7
Rover SD1 3500 manual   16.2    36.3    27.9
Rover SD1 3500 auto     19.1    31.6    23.5
Rover Vitesse Sport Turbo       25.6    47.5    38.0

*Triumph brochures of the period claims at a constant 50mph

From personal experience of vehicles in the above list, the Doly 1850 o/d
would do about 31-32 mpg regardless of how it was driven, Sprint 25-28, an
SD1 manual would achieve 28-30 and my current Vitesse Sport does 30-34.  In
all cases these cars are driven as quickly as safety allows and certainly
well above a constant 56mph!  Most surprisingly of all, the crude and
simple old MGB did pretty well on economy.

My experience of the Stag(o/d) is that provided it is not subject to
excessive amounts of harsh acceleration and braking as you would get in
Central London, it will return 25-28mpg driven rapidly.  On continental
motorway cruising at 80-100mph, it still turns in 28mpg.  The cruncher is
this.  In the 1974 fuel crisis when motorway speeds were restricted to
50mph, it would turn in less than 24mpg at a consistent 50mph on a motorway
trip from Lancashire to London and back.  On the next trip I kept to a
consistent 70mph, and it returned 27mpg.  

The major factors which influence fuel consumption on the Stag are;
1.      a heavy car, so hard acceleration eats fuel more than average
2.      small frontal area aids economy at high speed
3.      some roof configurations (soft-top, open) add a lot to drag
4.      smooth body shape aids economy (hard top)
5.      inherently very efficient engine aids economy
6.      very susceptible to bad tune (ignition, fuel)
7.      auto 'boxes eat fuel, especially the standard 3-speed

So, this was a long way to a short answer.  There is no reason to expect
that the 'magic' 56mph will give you good economy.  Best pay attention to
points 1-7.

Mike Wattam
Triumph Stag Register

p.s. this trawl for old information also yielded colour charts for the
Allegro and Marina, pretty exciting stuff eh?.  First to offer over £100
gets these!