Solar System tests disfavor $f(R)$ gravities
  Using the elegant method employed recently by Erickcek, Smith and Kamionkowski, on the premise that the space-time of Solar System is described by a metric with constant-curvature background added by a static perturbation, we show that many $f(R)$ gravities are ruled out by Solar System tests. 
Xing-hua Jin, Dao-jun Liu, Xin-zhou Li