Still, in the wide open spaces of our test location in Utah, and on roads generally built to accommodate supersized pick-up trucks, the GLS hides its size surprisingly well. You quickly become adjusted to it when behind the wheel, helped by the machine’s phalanx of cameras, sensors and other driver assistance systems. That said, we suspect its dimensions might cause some nervous moments on the UK’s tighter roads.
Although there has been considerable focus on passenger comfort, Mercedes hasn’t forgotten about the driver. Given its size and kerb weight (2490kg), the GLS handles relatively nimbly, aided by the smooth ride of the air suspension, a system suited to a car of this bulk.
It likely helped that our test car was fitted with 21in tyres and Mercedes’ E-Active body control system, which constantly scans the road and can adjust the suspension settings to suit. Neither will make it to the UK, with 22in tyres standard and the E-Active system not being offered on right-hand-drive cars yet.
A run in a GLS 580 without the E-Active system (and powered by the 4.0-litre V8 mild-hybrid petrol engine that sadly won’t be offered in the UK, either) suggested that the ride was marginally hampered without when tackling sharper corners or rougher roads.
The sole engine destined for Britain at launch will be a 325bhp 3.0-litre diesel. Once the initial effort of getting the hefty GLS moving is done, it offers brisk progress, with plentiful power and torque on tap when needed. It’s quiet, and well suited to the sort of mileage GLS buyers are likely to be doing. European fuel economy ranges from 28.9 to 32.8mpg on the WLTP cycle (the final UK figures are yet to be determined).
Although the GLS 580 won’t reach the UK, the 450 version, powered by a 362bhp 3.0-litre six-cylinder in-line petrol engine, is due next year.
Regardless of powertrain, we suspect GLS buyers are unlikely to do too much off-roading, although Mercedes engineers have expended considerable effort on ensuring it can tackle tough trails with aplomb. Selecting the optional £1495 Off-Road pack gives the GLS extra drive modes, a low-range transmission option and a torque on-demand inter-axle locking system, which made relatively easy work of the mountainous Utah ATV trails we were invited to try it on.