hey guys

ever since i got my coilovers installed and upgraded from 16's to 17's i've noticed my car seems to float at high speed like on the highway. the back end seems to move and sway alot. car is fine at 60K or less.
I was wondering if i would have to adjust the damper of my coilovers at the back to make them stiffer to recitfy this issue? i got told i needed to 'back my suspension off'.
what is a good setup? i.e slightly softer at the front and full stiff at the rear.
please advise

cheers