according sa KYB website, best way to know kung sira shocks is a test drive. kapag may naririnig ka na parang bouncing sound sa rough (yun labas na bato sa concrete, hindi lubak) road, time to have it checked. i just replaced mine, una diagnosis is 1 lang may sira, pero i opted to replace 2 sa front, lumabas below par na ang performance ng isa, yun isa sira na talaga, as in naitutulak pababa ng isang daliri at hindi bumabalik until 30secs. marami may free estimates, have it checked.