Cab over

Vintage COE: 1942 Chevrolet

Preserved International Harvester Metro Van in Portland, Oregon in 2012

The first truck in the United States was built by Autocar in 1899 using a format then called "engine-under-the-seat" and was available with optional 3.7 or 6.0 kilowatts (5 or 8 hp) motors.[1] Although early Autocar trucks were not exactly "cab-over", since the truck did not have a cab, per se, they were the fore-runners to COEs. The Sternberg company of Wisconsin produced cab-over trucks as early as 1907, though by 1914 only their seven-ton model was a cab-over. They reintroduced the cab-over layout in 1933 with their "Camel Back" model, which allowed the cab to be tilted to access the engine.[2]

The introduction of the first modern cab-over layout in the United States is credited to industrial designer Viktor Schreckengost, who, with engineer Ray Spiller, designed a cab-over truck for the White Motor Company in 1932. Schreckengost was later joined by other designers such as Raymond Loewy who designed the Metro series of vans and trucks for International Harvester. The bodies for these vehicles were initially produced by the Metropolitan Body Company (MBC). The company produced a wide variety of truck and commercial bodies for several vehicle manufacturers such as Chevrolet, Ford, Dodge Bros., and International Harvester until 1948 when they were purchased by the latter. MBC was instrumental in the development of COE route delivery bodies in the 1930s.[3]

The laws of the time limited overall truck length to 12.8 metres (42 ft) on highways. Setting the cab over the engine and front axle shaved several feet off the length of the tractor, feet which could then be added to the length of the trailer while keeping the dimensions of the entire truck within the permissible limit. Schreckengost patented the design in 1934.

Autocar reintroduced the engine-under-the-seat format with their Model U in 1933, which became a staple of U.S. roads and the U.S. military through World War II and well into the 1950s.[1]

White-Freightliner introduced its first tilting cab-over design in 1958, which allowed the entire cab to tilt forward for access to the engine.[2]

The 1962 Sisu KB-112/117 was the first European serial produced truck with a hydraulically tiltable cabin, enabling easy access to the engine.

A Mack F series truck

In Class 8 tractors (using the US designation), the cab-over design allows the vehicle's wheelbase to be shorter than in the conventional arrangement, wherein the engine is placed in front of the cab, covered by a horizontal or sloping hood that opens to allow engine access. Its shorter wheelbase allows cab-over semi trucks to have a shorter overall length, thereby allowing for longer trailers to be used. For light- and medium-duty solid- or rigid-axle trucks, the cab-over design requires less length for the cab and engine, in a given wheelbase, and therefore allows a greater length for the truck body or load area.

In both class 8 tractors and light- and medium-duty vocational trucks, the cab-over-engine design gives the COE model an advantage in maneuverability over a conventional model. And since COEs are generally lighter than conventionals, they can often haul heavier loads, given equal gross vehicle weight rating (GVWRs) and gross combination weight rating (GCWRs). Despite the COE designs' being smaller in general, over-the-road tractors can still be fully equipped with single or bunk beds. Also, lack of a hood gives better visibility to the driver and a tighter turning radius, and significantly reduces the forward blind spots.

One critique is that the shorter wheelbase in the COE semi-trucks gives a rougher ride than those with conventional cabs, as the driver's seat is above the front axle. In the 1970s, COEs used to be noisier, because the engine is directly below. This was an important consideration back then: Interior noise in the cab was between 80 and 90 db(A), creating an unhealthy work environment.[4] As of 2017, US long-distance trucks provide an interior noise level of 60–70 db(A) at highway speed, while European long-distance trucks, all built as a COE, provide a level of 60–65 db(A). As highway speeds are a slightly higher in the US, this performance can be viewed as equivalent.

Because of their flat front design, early COE semi-trucks had significantly worse aerodynamics than conventional tractors. Modern cab-over designs, in both semi-trucks and light- and medium-duty models, have improved aerodynamics significantly over early models, but often still have higher drag coefficients than their modern conventional-design counterparts. This works against fuel economy, and offsets some of the improvement in fuel consumption garnered from the lighter weight of the cab-over truck when running less than fully loaded.

Although the tilting cab gives comparatively unobstructed access to the engine, its deployment causes unsecured items in the cab and sleeper (if equipped) to fall onto the windshield or under the instrument panel.[5] Vehicles without a tilting cab will usually be equipped with removable floor panels through which mechanics can access and service the engine. In Europe, Mercedes-Benz was the last manufacturer to use such panels instead of a tilting cab, with the last non-tilting cabs produced well into 1983.

Safety aspects

Isuzu Elf Box truck

Tatra 813 Kolos 8x8 Drive Military Truck

Land Rover 101 Forward Control with radio-vehicle body

Truck occupant safety depends on survival space within the cab, with "rollover" being the most significant heavy truck accident causing occupant casualties. [6] In the 1950s, when many truck cabs were still wooden structures, knowledge about the most common accidents was already established, and led to the first mechanized truck cab crash test in 1959, performed by Volvo. The test became a Swedish standard, and was adopted by the European Community in simplified form as ECE R-29 in 1974. During the early 1980s, the safest place for a truck driver was a European truck, usually a cabover.

As decision-making is primarily based on human perception, the results of safety statistics might not be considered valid. Motor placement before or under the cab does not have much influence on the results of rollovers. Behind the danger of a rollover, heavy truck on heavy truck crashes are the second most relevant reason for occupant casualties. With a 1980s US conventional, the result of such a crash was: Frame, front axle and wheels would go under the truck in front, while the motor got pushed into the cab (which was very small in a 1980s conventional).[7][8] Contrary to these real-world results, the motor in front, which would crush the truck driver in an crash, was nonetheless perceived as "protection", and this perception was an important factor for the adoption of these trucks in the US, during the 1980s.

Both conventionals and cabovers need structural protection against rollovers, and special protection against massive objects at the height of another truck body. The survival space should be able to move backward on the frame.

In military use, the COE design increases the chance of crew injury or death in the event of running over a landmine. This is because the tire that detonates the mine is directly below/beside the driver.[9]

• Terminal tractor
• Tractor unit
• Kei truck
• List of Low Cab Forward trucks

Wikimedia Commons has media related to Cab-over-engine trucks.