I have a Toyota 4Runner which has 2WD, 4WD (high) and 4WD (low).  I
often drive to the mountains and when conditions are bad use 4WD
(high) with my S&M tires.

However I am thinking about bringing snow chains and have a few
question regarding their use on 4 wheel drive vehicles.  I have done a
fair amount of research on my own, and the jury seems to be equally
divided about whether or not to put them on the front tires or the
rear tires. Both approaches have benefits and downsides, and both
sides argue their case strongly...

So what I am looking for is this :
1) Is there even a safety benefit of using 1 set of tire chains on a 4
wheel drive vehicle over just using 4 wheel drive on its own?  Has
this been measured - any data?
2) Is it better to just use 2WD and chains on the rear wheel (rear
wheel drive) rather than 4WD and chains on the rear or on the front.
3) Can you refer me to some definitive, authoritative source - such as
a Highway Patrol web site in a snowy state where the rear-front issue
is discussed and advise given.  I have loads of anecdotal information
from both sides already.

thanks

Peter

When I reseacrhed an almost identical question, the consenseus was if
you are using 4WD, to put the chains/cables on ALL 4 TIRES:

4WD Pickup Truck - Where to put ONE pair of chains for ice and snow driving.
http://answers.google.com/answers/threadview?id=442812

Coming from an area with lots of mountains and winter snow:  You
ALWAYS put chains on the front wheels of a 4WD vehicle if you're only
going to use one set...there is no other correct answer.  If you need
2 sets you're driving in some extremely nasty conditions.

See what I mean - 2 different sets of advice.. maybe there is no right answer?

cynthia says always put them on the rear in the link she includes and
phantomflyer says always put them on the front. I am off to Tahoe soon
- let's see ;-)

Peter
p.s. Obviously on all 4 tires is better, but I knew that already ;-)

yes, all 4 wheels with will help in extremly low traction driving, but
for normal ice and i believe that you should put them on the front
wheels as phantomflyer does, but ill provide some reasoning

1. (obviously) the two front wheels steer the car and should need more traction

2. when braking the front wheels provide about 60% of the force. this
is why front brakes are always bigger/better than the rear, if the
rear brakes were bigger/better it would cause the rear end of the car
to swing around (try driving a racing go cart)

Yup thats what I was going to say. But also i suggest getting a good set of tires.
     Maybe yokohama geolander m/t, bfg mudterrian t/a ko, or goodyear
Mt/r which I personally like. Probally get desent prices from
tirerack.

i too read that article about where to put chains on a 4wd.  here's
the reasoning that doesn't make sense to me - what that article also
says is this:

" A vehicle needs traction for 3 things: acceleration, steering and braking.

Snow and ice do not provide much traction.
4WD provides 100% more traction than 2WD. 4WD has twice the amount of
traction than 2WD. The 4WD advantage in snow is marginal over 2WD.
Good winter tires make some difference - but not significantly.
We all know rubber on snow and ice produces very little traction. As
said before 4WD has twice the traction of 2WD - so you get twice the
amount of very little. Still not very much. Definitely not enough to
be really safe. Only aggressive steel chain links put between rubber
and the surface are able to elevate traction to a safe level. A
vehicle needs traction for 3 things: acceleration, steering and
braking.

Snow and ice do not provide much traction.
4WD provides 100% more traction than 2WD. 4WD has twice the amount of
traction than 2WD. The 4WD advantage in snow is marginal over 2WD.
Good winter tires make some difference - but not significantly.
We all know rubber on snow and ice produces very little traction. As
said before 4WD has twice the traction of 2WD - so you get twice the
amount of very little. Still not very much. Definitely not enough to
be really safe. Only aggressive steel chain links put between rubber
and the surface are able to elevate traction to a safe level."

so then it seems the obvious solution is to put your 4wd into 2wd and
put the chains on the front axle - just like any normal 2wfrontd. 
after reading this:

"Chains mounted on all 4 with 4WD/AWD - perfect acceleration, crisp
steering, super braking. However, part time systems will show
understeer. Full time 4WD systems are best. This is what everyone
should have for snow and ice. Be careful anyway.
Chains mounted on front axle with 4WD/AWD - good acceleration, good
steering, good braking. However, since the rear wheels have no lateral
guidance, the rear end might come around - fast. Not good. Feather
your brakes. Go slow.
Chains mounted on rear axle with 4WD/AWD - good acceleration, lousy
steering (no lateral guidance), so so braking (remember, 80% of brake
force goes to front wheels and isn't put to use without chains). No
fishtailing. Best compromise for 4WD with only one pair of chains. Go
slow."

that last line "best compromise for 4wd..." seems ridiculous.  give up
good braking and steering just to counteract possible rear-end drift? 
and like i said above, if it's the 4wd (drive going to all tires),
that causes that tendency to drift (because the wheels will spin
instead of just track), then the best solution (if you have to add
chains), is to switch to 2wd and put the chains on the front (im
assuming all 4wds when switched to 2wd drive the front axle).

no?