From the factory, engine and transmission mounts are rubber and thus a wear component. Worn out engine or transmission mounts create sloppiness and a disconnect between the driver and your BMW's powerplant. If your vehicle is purpose built for the track, we recommend solid engine and transmission mounts. These have zero deflection, but come at the expense of added NVH (noise, vibration, and harshness). Poly engine and transmission mounts offer a good balance between OEM rubber and solid mounts for those with mixed purpose vehicles, offering great performance and connection with little sacrifice in terms of NVH.