[tgtweak]

Lots of conjecture. The reality is most of the drag is encountered on the trailer, tires and underside. This is the reason you now see "skirts" on almost all trailers, and the general reduction in distance between tractor and trailer and not long airplane-like tractors.

More important to fuel economy is maximizing cargo per trip, as having 20% more cargo in the trailer has no impact on aerodynamics and minimal contribution to rolling resistance and acceleration losses. This is the main argument against the length restrictions in the EU. Longer trailers + more aerodynamic tractors would lead to a significant increase in fuel economy - albeit at the cost of road safety: EU records nearly identical deaths per year for trucking related accidents as the US - around 5000 - but has 300% as many trucks on the road and 50% more population than the US.