VNL62T780

VNL62T780
VNL64T780

V= Volvo
N= North America
L= Long Hood
6= Number of Hubs
2= Number of Hubs that drive the vehicle
4= Number of Hubs that drive the vehicle
T= Tractor
780= Cab/Sleeper Model

So in Layman's terms, they both are rear tandem axle trucks.

The VNL62 is a rear Tandem Axle Truck where only (1) one of the Rear Axles is powered, (the #2 position), the other Rear Axle (the #3 position or trailing) is a Tag Axle.
(No Inter-Axle Differential) (6x2)
(2) two Hubs powered)

Customers spec'd this type of truck for fuel economy, lighter weight (no Inter-Axle and only (1) one Differential) and less drag, (when equipped with a low rolling resistance SmartWay approved ECO tire of a ribbed design, instead of a lugged design) at the expense of traction, especially in the wintertime.

These trucks are usually spec'd with Traction Control to offset the disadvantage of not having a Inter-Axle Differential setup.

The VNL64 is a rear Tandem Axle Truck with all of the rear Axles powered. (#2 position at all times)

The #3 axle position is not powered until the Inter-Axle is locked into position using the switch on the dash.

(Equipped with a Inter-Axle Differential)
(6x4)
(4) four Hubs powered

This is the traditional spec'd truck that you will most likely have driven, and that has been commonly used the most for decades.