Where do I get them?

america's tire company.

costco

that used tire place on south van ness @ 19th

you get what you pay for though

i usually go all the way down to sears in tanforan for all 4 new tires

Costco but be prepared to WAIT all frickin' day.

Rynck is the best.  Great prices and great service.  Closest place to SF is Alameda.

What Maggie Said - American Tire Company

If you want the absolute cheapest you can find a used tire shop.  Surprisingly enough you might find some good tires there.  I used to go to a used tire shop to find tires that I could waste away at the drag strip.  I often found Pirelli's, Firestone, Bridgestone, and Goodyears for super cheap with lots of tread still on them.

If you are looking for brand new tires then either tirerack.com or a place like America's/Discount Tire Co.

Big O...  then tell them you would buy their tires if they can match Tirerack.com prices.    Tirerack or Discount Tires are the cheapest tires prices for any tire you can find.  You should be able to get four tires for the price of three.   Remember.. most places will hit you up at least $45.00-$90.00 for alignments if the need them.

some costcos have a deal right now where there is a $60 discount when you get 4 tires. check it out

At Costco the tires for my car (a VW Beetle) were really expensive...

If you can wait, I recommend tirerack.com. Otherwise try Paul's - yelp.com/biz/pauls-batte…

They are fast, honest, and can find you a great deal on tires. I saved about $400 in total by using them. And they were done in an hour!

Oh.. And Paul's does free tire repair if you get a flat, and they balance and rotate for free every 5K or 6 months. They ROCK! You can have your tirerack.com tires shipped there too if they don't have your specific tire in stock.

Larkin Bros. on South Van Ness

FYI: Costco's name brand tires are cheap because it's specially made for Costco. It wears and tears much faster. I suggest buying it elsewhere.

I love my $50 13 inchers.....

I vote for Costco. I have been buying tires from them for years. They have a location in The City at 450 10th Street, SF 94103.
They have a very good replacement/warranty policy. Once they replaced a two year old tire for free! More recently, I had the tires for my Volvo replaced and they pro-rared the cost of the replacement, since the former tires were also purchased at Costco, even though the tires were well worn. Make sure you come 30 minutes before they open, otherwise you will wait all day. Also, they do have a promotion through February 3 where you can get a $60 discount. A one year basic membership does, however cost $50.
Check out: costco.com/Tires/Landing…;eCat=BC|3960|3961&lang=en-US&whse=BC&topnav=

Its important to recognize that tires are all you have between controlling a 2000LBS of steel, 1LBS of CDs and 1/2 Pounder McDonalds burger on Bay Area unmaintained roads.   When your car does go in... things to ask for, are alignment costs, disposal fees, rotation / balancing, shock and brake test, steering and wheel adjustments, with possible other other services.    The concept of cheap tires might be so for your pocketbook, but the effort and environmental issues in creating a tire is entirely another thing. Also, instead of risking your life (and mine) on tires that are cheap and underated for the cars use or size can forever change lives.  If you can't afford proper tires for a car, take the bus.  
Some Brands worth looking into..

Nitto, Bridgestone, Michelin, Pirelli, Firestone, Goodrich and Goodyear

definitely check out tirerack.com first.  read their tire survey to see which tire in the class you're looking for, performs the best.

then check out discounttire.com (America's Tire Co. website) and discounttires.com (SoCal tire chain, not affiliated with America's Tire Co.).  I just bought some new tires for my truck from discounttires.com and they had the tires about $30-$40/tire cheaper than tirerack or America's Tire.  Big-O, I've been told, will also give you deals too...if you mention you can get the tires at tirerack for cheap.

costco and tirerack. but don't buy cheap tires. Get the good ones, insurance and hospital bills are not worth it.

tirerack.com is usually cheaper than costco, in my experience.

I think Firestone has great deals especially financing and all