A few years ago, on my way up to Tahoe, I had a brief chat with the poor soul manning a highway 50 chain control checkpoint during the slow, snowy overnight shift. I asked, "Is there ever a situation where I would require chains on my Subaru (AWD Legacy)?"
The answer I received was a very definitive "NO". Other law enforcement officers, CalTrans personnel and high-country residents have indicated the same.
However, a lot of low-landers I work & play with (some 4WD owners) seem skeptical of this advice, and a current thread here (Snow chain required to sugarbowl) would seem to indicate the advice I've received may not be entirely correct.
FWIW, I chuckled to myself Thursday morning cruising the crud up Hwy 80 from Auburn when I breezed by a Subaru Forester with chains on the rear wheels only.
From experience, I know the Subarus (at least the manual transmission variety) are very sensitive to minor differences in front vs. rear tire diameter. If I wait too long between tire rotations, giving the front tire the opportunity to wear down sufficiently more than the rear, I begin to develop an noticable and irritating (and mechanically harmful) driveline vibration.
Point being, if I were in a situation where I'd use chains in a Subaru, I would presume I would want them on all four tires.
This might not be the case for other manufacturers' "AWD" vehicles where front and rear output is not coupled full time.
A quick web search dug up this interesting thread on the subject: http://forum.ski.com.au/scripts/ulti...2;t=000014;p=0
Here's an informative excerpt from that thread, a reply from a Subaru engineer:
"Many thanks for your email. To answer your question, yes- the Subaru All-Wheel-Drive system meets the exemption & snow chains would not be required.
"Our Chief Engineer has recently made an enquiry to VicRoads & received this reply:
"1. VicRoads did not release any bulletins, acts or regulations related to snow chains and A-W-D vehicles.
"2. The VicRoads Act states that snow chains are required on Buses that carry over 12 persons.
"All Subaru vehicles from approx: MY1997 are fitted with a permanent All-Wheel-Drive system. If for example a front wheel looses traction, the drive will go to the rear. The drive is always available at both front and rear wheels, unlike some other brands that wait until wheel slip occurs. In addition to this & dependent upon model, some pre-MY1997 Subaru vehicles were also fitted with an All-Wheel-Drive system.
"The Subaru owner's manual indicates that driving on snowy grades or icy roads may require the use of snow chains, in which case put the chains on the front wheels. As to when the chains are required, this is determined by Government regulation or the directions provided by the Authorities in the snow field/park that you enter.
"If the front and rear wheel sizes vary; and the vehicle is driven over a prolonged period, eventually damage can occur to the Viscous Coupling centre differential fitted to manual transmission Subaru's, or to the Transfer Clutch fitted to automatic transmission Subaru's.
"The A-W-D Subaru Automatic Transmission is fitted with a full time All-Wheel-Drive transfer clutch that is electronically controlled. This ensures that the vehicle maintains 50:50 traction levels at the front and rear wheels. Torque transfer is dependent upon tyre to road contact to ensure no wheel slippage occurs.
"The A-W-D Subaru Manual Transmission is fitted with a Viscous Coupling centre differential, which transfers a full time 50:50 drive to the front and rear wheels dependent upon tyre to road contact to ensure no wheel slippage occurs.
If you look at the Subaru All-Wheel-Drive system as a whole, in both Manual and Automatic transmission. Based on their operating principles, the Subaru A-W-D system outperforms most other 4WD systems; hence snow chains may only be required in extreme conditions on the front wheels for steering purposes, NOT for tyre to road surface slippage."