Mercedes-Benz 2011 GL-Class Operator's Manual page 360

Wheel/tire combinations
358
as standard equipment or as an optional
extra.
If you want to equip your vehicle with
approved winter tires, it may be necessary
to obtain wheel rims in the corresponding
size, as the size of the approved winter tires
may differ from the standard tires. This is
dependent on the model and the
equipment installed at the factory.
Tires, wheel rims and further information
can be obtained at a qualified specialist
workshop, e.g. an authorized Mercedes-
Benz Center.