Suspension systems that not only transform the stance of the vehicle but also maintain ride quality and improve upon handling are what Dinan suspensions are known for. This is accomplished by pairing springs sets with bump stops, spring perches, or both to maintain suspension travel resulting in a smooth ride while also improving mechanical grip and handling. This is what makes Dinan suspension systems unique. While we sell each component separately, it is highly recommended that both the spring sets and the supplemental ride quality and handling kits are used in tandem in order to maintain the Dinan quality standards our customers are used to. Experience the Dinan difference with this combination and enjoy the ride it provides. Dinan's Performance Spring set for the G01 X3 M40i and G02 X4 M40i provides greater control over body roll by virtue of carefully calibrated spring rates. Additionally, Dinan lowers the car for improved suspension geometry and an even more aggressive stance. The Dinan springs are CNC wound with high tensile chrome silicon wire and shot-peened for stress relief to last the life of the car. The increase in stiffness will reduce the rear suspension compression under acceleration and front suspension compression (or dive) under braking, giving your car a more controlled feel. The Dinan performance springs will also provide a noticeable improvement in grip for high-speed driving situations that will inspire confidence in your car's capabilities. The reduced body roll makes the steering more responsive to driver input and will be noticed at low speeds up to the top speed of the vehicle.