As I mentioned a couple of installments ago, it is very easy for
recent inductees into the truck spec and purchase fraternity (no gender implied)
the get lost in the nomenclature of truckdom. Complicating that fact is that terms
are a moving target. Language it seems is malleable, continually bending and
accommodating new interpretations and usages. Example: When I was a kid, a dope
was someone behaving stupidly, then somehow it became slang for drugs of
various types. More recently it has been adopted to mean something profoundly
cool – IE: “That bike was dope, man!”. At least there is good news in truck’ese;
these shifts and changes happen more slowly, largely due to the usage being technical
in nature.
Today’s topic: Chassis stuff
Once upon a time I remember treading water trying to absorb all
the TLA’s (three-letter acronyms), so I now pass along a few more of these
trinkets to hopefully help-out others on that path and reduce some head-scratching.
So here goes.
CA: “Cab-axle”- the distance between the back of the cab and the
centerline of the rear axle (sorry, only two letters not three, but important
in both light and heavy trucks). This determines the type and dimension of a
bed you can put on a truck, the dynamics of the truck’s balance and how
maneuverable it will be once in service.
CT: “Cab-trunnion”. Not unlike the CA term, but with a different
application. The trunnion is the center pivot from which the rear axles
articulate on a tandem drive-axle truck. On some tandems (mostly air-ride
suspension jobs), there is no trunnion per se, so the term has come to mean the
centerline between the two rear axles. That’s where the distribution of the
rear load will rest.
“Clean” CA: having defined CA, it is sometimes important to know
this facet of that dimension. “Clean” means there are no protrusions and/or
equipment mounted on the outside of the frame rails between the cab and the
rear spring hangers. No so important if you are building a dump-truck, flatbed
or 5th-wheel tractor, but hugely important if you are mounting a
utility bed or something else that sets down over and extends below the frame.
BBC: “Bumper to Back of Cab” – In our world this isn’t the home of
British sitcoms, but rather the distance between the front bumper and the rear
of the cab. This is steered by physical engine size and cab configuration and ultimately
determined by the end use of the vehicle. IE: over-the-road trucks typically
use big-bore engines that take a lot of real-estate. They can have a long(er)
BBC as they aren’t required to do sharp turns continually in city-traffic &
stretching the truck smooths out the ride and reduces front axle requirements.
AF: “Axle to end of Frame” The distance from the centerline of the
rear axle to the rear-most frame-rail end. This dimension can be specified on
big-trucks and needs tuning to accommodate certain upfits.
OAL:” Overall Length”. ‘Nuff said?
COE: “Cab-over-engine”. Once as common as childhood fears due to
Tractor/Trailer length restrictions, Cabovers are now scarce. From their
enclosed-cab debut in the 1930’s through the mid 1950’s the term meant a
portion of the cab was mounted up over the rear part of the engine, but the
truck still had a sort of a nose. However, by 1954 a COE built by a little
company named Freightliner had lost virtually all signs of what had become a
vestigial nose and gotten a slab front-end, so the term evolved. Now the engine
was truly under the cab, so what do we call the short-nosed trucks with the
engine partially under the cab now?
LCF: “Low-cab/Forward”. Fine points will be argued as to when, but
by observation trucks that had been categorized as Cabovers before the
slab-front Freightliner was introduced were now starting to be called LCF’s
after its introduction. And indeed, on these trucks the cab sat forward from
where it was on a “conventional” truck and was “low” enough that there was a
pronounced hump in the floor where the engine stuck back under part of the cab,
followed by a flat floor. Look up a picture of a GMC “Cannonball”; slang term
for a style of road tractor popularized by a 1958 TV show of the same name. Yes,
the cab is still well up there, but not quite as far up as what Cabovers had gone.
This LCF term evolved further though. In certain more recent specialty
applications (think front-loading trash trucks since the late 1970’s), the
operator is seated slightly ahead of the front axle with the engine behind.
This is to allow a very low cab-height for increased overhead clearance. Examples
would be the GMC/Volvo/Autocar Expediter and Mack MR688 series. No idea where
the term is headed next, so hold on for the ride.
Conventional: Like the name implies, the engine is out front with the
cab behind it. IE, the truck is in a “conventional” configuration. The Cabover’s
day in the sun ended sometime shortly after the 1982 passage of a highway bill
which lifted the 53’ length restriction (mentioned earlier) for interstate tractor-trailers.
Cabovers still have some advantage in urban settings were tight turns are the
norm, so they still enjoy some success in America (and even more in Europe) as
delivery trucks. However, they are a hard-sell to modern drivers covering mostly
open highway. Truck for truck, a conventional will be quieter and ride more
smoothly than a Cabover in the same application.
So by all means, jump in your LCF instead of your COE, as this may
help you manage your OAL due to the shorter BBC. Just remember your CT is
longer, so if you don’t want to clean your own CA, mind your turns.
© 2019 D.W. Williams
