This is a replacement part that in our Black Series application is over 200% stiffer than the original rubber bush to withstand increased loading seen by this position on the car. PFF5-1901GBLK provides +/- 0. 75 caster offset that can be adjusted on the car for improved steering feel. Additional caster will also create additional negative camber on turn giving improved tyre contact with the road under heavy cornering. For a non-adjustable version of this bush por favor use PFF5-1901BLK.