Disadvantages
Some drivers have complained, however, 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; and that the cabs tend to be noisier because the engine is directly below, though some of this is dependent on the amount of noise-dampening insulation used in the construction of the individual vehicle.
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. Vehicles without a tilting cab will usually be equipped with removable floor panels through which mechanics can access and service the engine. Unfortunately, some components might require servicing or replacement that either will not fit through the hatch or remain inaccessible. This necessitates removal of the engine by lowering it out from under the vehicle, a time-consuming and expensive procedure.
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 tyre that detonates the mine is directly below/beside the driver.
Read more about this topic: Cab Over