I have 4x4, on my SRW I always carried chains for all 4 only had to use them once coming out of Yosemite in really icy conditions R2 for my own piece of mind. On my 4x4 dually I carry front and rear chains but not dually chains, just for the outer rears only. So far I have not needed them but my fire department rescue vehicle which was a 4x4 GMC 3500 dually with an ambulance box we used chains every winter on the ridge where I worked and we only chained up the outer dually and never had a problem.