Wednesday, February 20, 2019

Truck’ese 101, Ver 3.0: Say What?


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