Think multi-mode... I live in North Austin (Duval and Mopac), and the folding bike and the train get me downtown easily. But a full-size bike will fit on the train too- they're usually empty.

Anyway, having experienced both Austin and SF, if I could afford SF, I'd be there now. Austin is brutal in the summertime with temperatures and humidity hovering in the 90's for 5 months straight- it's actually dangerous to strenuously cycle in the summer here (starting to get nice now though with highs merely in the mid-80's). The governor and the legislators are staunchly bible-belt Republican and legendarily corrupt- we have several unused toll roads that were no-bid construction contracts to the gov's buddies and state-guaranteed toll revenue to other pals of his- but nobody ever uses them since they're expensive and don't go anywhere; the traffic is worse than ever. Governor "Goodhair" vetoed the bike safety act SB488 (would have required 3 feet of room to cyclists when passing, among other things, overwhelmingly passed in the legislature); he said "bikes already have enough rights". Generally, it seems that people here think that Austin somehow invented hip and happening, but it's actually about 15 years behind the times compared to the coasts. If I weren't an economic refugee, I'd never have moved here, and as soon as the economy on the west coast recovers, I'm outta here.

I digress- OP *will* need a car in Austin. Being in a red state, the public infrastructure is weak at best, consisting of one train line to the north with limited schedule, and infrequent buses, with most things spread widely apart (cheap land and no land-use laws and no natural geographic boundaries means hundreds of thousands of acres of mini-malls along the arterials and suburbs between). OTH, SF's BART, trolley and bus system means that being car-free is quite possible, even preferable in the city- when I lived there, my car was used maybe three times a year- and you can join one of those car-share services for the 3 times the car is needed.