Judging by the photos, I would say the main design concern of these trucks was the ability to operate in tight spaces. Notice that there is almost no wasted space between the front of trailer and the back of the tractor. Also moving the trailer axles forward allows the truck to turn with less off-track*, but also puts a larger portion of the weight on the trailer axles, hence the three trailer axles and only one drive axle. The trailer’s kingpin (the thing that attaches to the tractor) also seems to be further back on the trailer (compared to US trailers) which would also help operation in tight spaces.
I don’t think these trucks would be very comfortable or stable for long straight highway trips.
The Cab-Over Engine design (COE or Cabover) allows for a shorter wheel base and therefore making tighter turns with the tractor, but does not affect off-track. The European tractor seems to have a slightly longer wheel base to accommodate the further forward kingpin mentioned above.
I must disagree with MC’s first two statements—
[li]The single tire (or tyre for you brits) design that replaces duel tires (AKA Super-singles) uses one larger tire with the same load capacity as two standard tires.[/li][li]Several mechanics I have talked to have complained that changing Super–singles is a pain due to their greater weight, almost twice that of standard tires, which weigh over 100 lbs. with the rim.[/li][li]With standard duel tires, if you have a blowout you can still drive a short distance at reduced speed to get it repaired.[/li][li]Super singles do see limited use in the US, particularly on spread axle trailers, but I am not sure what their advantages are.[/li][li]I don’t get to use the list command very often ;).[/li][/ul]
MC is somewhat correct on his third statement, US trucks must be designed to comply with the ‘bridge formula’ that sets limits on how close axles can be to each other. Also US trucks are limited (in most states) to 38,000 Lbs. per set of tandems (two axles), many states do not allow more weight for using a third axle (Michigan is one notable exception). I suspect the European design truck would not comply in many US states due to the axles being to close together and to much weight being carried on the trailer axles.
*Off-track – When turning a vehicle with a trailer, the trailer will follow a tighter radius than the tractor. This is why trucks must swing into the left lane before making a right turn.