Well, I read more of the reviews and amazingly some people got 30k miles out of these tires. I don't know how it is possible. The vast majority though change them at about 13-15k in average. Some only after 5k. So Cal has pretty nice roads trust me. The concrete might be a little rough at some spots but compared to Oregon where people drive with studded tire in the winter even when there it snows an average of 7 days a year...
I only have 3000 miles on my car and I only drove 800 of them as I bought it used. The rear are already down to 8/32" I usually change my tires with about 2/32" left so I am basically 1/3 through the treadlife already.
2000 Z3 2.8 TiAg (retired)
2002 330i Orient Blue (retired)
2005 330Ci TiAg (retired)
2009 Z4 30i Space Gray (retired)
2011 Z4 35is Space Gray
2011 535i GT xDrive Space Gray