I personally do not lock anything on ice / snow.
From experience, I can tell you that a Discovery driving at highway speed (6 lane highway, probably 45 MPH) at dawn in light-snow-falling-and-melting condition hitting a icy (1/2" layer of ice) bridge can avoid a Renault Super 5 while that car was doing two 360 degree loops.
The Discovery did not have the CDL locked, my mom was driving it and I was driving the other car. I got surprised, _touched_ the brakes trying to slow down... too late.... big error! nobody got hurt, touched the side rail, needed fender job only, drove the remaining 100 miles; can't say the same about the totalled ford-taurus-equivalent car 200 yards away.....
(Renault Super 5 info: http://jpracing.racerplanet.com/modu...thumbs/184.gif
Here is my (unverified) theory:
- On ice and snow on regular paved roads, you want to avoid any tire slipping which a locker could induce. This is also why you typically will drive a 5-spd "one gear higher than normal" (not sure if automatic can do anything about it except keeping a very very light foot).
- On ice and snow on non-paved road or deep snow on paved roads, I'd lock the CDL because in this case, you are likely to need to go up/down irregular terrain and would loose traction quickly otherwise plus you are at much lower speed (max 25 mph?).
Now, I'm sure someone with more experience can give us the "official" word.