Bilstein 5100 shocks utilize a monotube design, with a 46mm digressive piston, to increase road handling characteristics both on and off-road. The single tube body allows for rapid heat transfer between the shock oil to the shock body, and then dissipated further to reduce shock fade. German engineering combined with US manufacturing ensures optimum performance and longevity for upwards of 100k miles (real customer feedback!). The 5100 series is more compliant in tougher situations and off-road terrain compared to the 4600 series. Factory spec vehicles should use the 4600 series shocks as the valving is more appropriate for daily driven vehicles and pavement environments.