Before you condemn your tires make sure you check out your swingarm bushings,steering head bearings,fork integrity(proper oil level,good seals,etc.),wheel trueness.
Man....you shoulda seen the slop in my swingarm a few years ago before I rebushed it.Everytime I got to speed on the freeway....got the shakes goin' but when I hit that grooved concrete sh!t.......man...I thought I was goin' down!!