I live in the California Sierras, and snow storms and road controls are a part of life around here.
There are 3 levels of requirements:
* R1: Chains, traction devices or snow tires are required on the drive axle of all vehicles except four wheel/ all wheel drive vehicles.
* R2: Chains or traction devices are required on all vehicles except four wheel/ all wheel drive vehicles with snow-tread tires on all four wheels.
(NOTE: Four wheel/all wheel drive vehicles must carry traction devices in chain control areas.)
* R3: Chains or traction devices are required on all vehicles, no exceptions.
For all practical purposes under R3 conditions you should just stay at home, or be in a motel.
4x4's do fine under R2 and R1 if they have snow tires. The larger the vehicle the more difficult they are to handle in snow and ice.
Unfortunately we have a lot of people driving around who are not used to snow, and many of them can be hazardous to your health. I think this is why California DOT puts up chain controls at the first sight of snow.
Nevada on the other hand just tells drivers that snow tires and or chains are required and then leave it up to the driver.
As far as chains go, a single set on the rear, I use the type with the diamond pattern. If you had a second set they would go one the front tires to aid with steering and traction.
If you are running chains front and rear you either shouldn't be on the road, or you are extracting yourself from a difficult situation and are heading back home or to a Motel.