Prothane polyurethane bushings are manufactured firmer than the O.E. Not only does this increase the longevity of the bushing but gives the suspension a boost in handling performance. With a firmer bushing, there will be a slight increase in NVH (noise, vibration, and harshness), but the performance boost far outweighs this slight increase. Replacing the entirety of your suspension bushings maximizes your handling and ensures it stays that way for a long time.