Chains can be fitted!
First reason: they will give a more comfortable ride.
However many opinions on this forum suggest the Airmatic will compensate for this and a smooth ride is still assured. I have basically confirmed this in my test drive with 20" and airmatic.
Second reason: Mercedes handbook advises chains should only be fitted with 7.5x17, 8.0x18, or 8.0x19 rims.

The W164 manual says the same thing, so I ordered it with 18" rather than the then standard 19". When I fit the chains, I have adequate but not excessive inner guard clearance.
I did notice the W166 seemed to have a bit more room so the dealer was kind enough to let me fit my chains on the 20" demo wheels.
Result: There is more clearance on the inner guard on the 20" W166 than with the 18" W164. Due to the larger width and overall diameter of the 265/45R20 tyres, the radius of chain on the outside is larger, so there is little chance of rim damage despite the rim being larger.
So fortunately the dealer was able to modify my order, and now the 20" wheels will be supplied.
If I lived in Colorado let alone Canada, I would be out to purchase some Nokian snow tyres straight away.
However I have two homes, one just out of Melbourne, the other 400 km away in the Alps. The Rangers provide $500 bonus prizes for anyone who fails to carry chains in the mountains, and whilst 4WD are usually exempt from fitting them, they are occasionally required.
Last weekend there was a blizzard which gave me a testing time without chains, but a GL500 was driving around town with chains. The driver said he was annoyed at having to fit them until he hit the storm.
Yes I know you have heavier falls than the pic shows, but we still have to be prepared.
Last edited by iankayem; Jul 1, 2012 at 09:49 PM.
Size 255 fits 255/55R18, 255/50R19 and 265/45R20. These are the ones for the ML.
The GL had size 266 for the 275/50R20.







