This article is from the California Driving (and Surviving) FAQ, by "George J Wu" firstname.lastname@example.org with numerous contributions by others.
from ajh@Xenon.Stanford.EDU (Alan Hu) on 10 dec 1992:
According to my memory according to a pamphlet put out by CalTrans a
few years ago, chain requirements come in three varieties:
1. Chains required. Four-wheel drive or snow tires OK.
2. Chains required. Four-wheel drive with snow tires OK.
3. Chains required on all vehicles, including four-wheel drive.
Usually you'll see #2, although I've seen #1 before. The pamphlet
said they'll usually close the road instead of doing a #3. Tires
marked M/S or M+S qualify as snow tires [CVC 27459]. Chains must be
installed on at least two drive wheels [CVC 27459]. Four wheel
drive vehicles must still carry chains.
The chain requirements used to surprise my non-CA friends. If you
haven't seen them enforced yet:
You'll see the Chains Required sign. Lots of people will be
pulled off the side of the road putting on chains. Various
people wander from car to car offering to put your chains on
for a fee (but they're not allowed to sell chains). Farther
down the road, a checkpoint checks EVERY car that tries to continue.
If you don't meet the chain requirement, they turn you back.
In short, if you're driving in the Sierra, they're very good to have.
Also, there's a toll-free CalTrans road condition number [see the
phone numbers question in this FAQ].
from email@example.com (Dan Hepner) on 9 dec 1992:
Most people could indeed drive the passes when snow covered without
chains, IF the road were more or less clear of other cars. But in
stop-n-go driving, common in the Sierra during a snow storm, required
chains are what prevents total chaos.
-- And, if so, what would y'all recommend?
For infrequent usage, such as having the bad luck to hit snow on a
Sierra pass during a drought, consider the cable type. For frequent
usage, or maximum effect, use the real thing.
Watch out for oversized tires, or even maximally sized tires on front
wheel drive. The chains can extend wide enough to hit other front-end
components. Cables mitigate this problem.