Here's the online owner's manual for the RC350: http://drivers.lexus.com/t3Portal/document/om-s/OM24636U/pdf/OM24636U.pdf
Page 614 is where the tire pressures are listed. Not too sure but your rear tires could be under-inflated.
Page 614 is where the tire pressures are listed. Not too sure but your rear tires could be under-inflated.