BMR Suspension CB005R Mustang Cradle Bushing Lockout Kit (15-17), 1 Pack

Solidifies the rear end so it's not so squirmy under acceleration. I'm not drag racing, so I'm not concerned about wheel hop or 60' times, but it's a noticeable improvement in every day driving. This and a front end X-brace are two mandatory upgrades for any S550 imo.