ST Suspension XTA Height/Rebound Adjustable Coilover Kit w/ Top Mounts for 03-08 BMW Z4 (Z85)(18220804)

ST Suspension XTA Height/Rebound Adjustable Coilover Kit w/ Top Mounts for 03-08 BMW Z4 (Z85)(18220804)For those who demand the absolute best performance comes the ST XTA coilover. The full driving behavior of your car can be adjusted using KW damper technology along with an adjustable aluminum uniball top mount for fine tuning of the camber and caster! Performance driving in mind ST XTA coilovers feature KW damping technology which allows the suspension to be made either stiffer or softer depending on the driving conditions. This damping adjustment is

For those who demand the absolute best performance comes the ST XTA coilover. The full driving behavior of your car can be adjusted using KW damper technology along with an adjustable aluminum uniball top mount for fine-tuning of the camber and caster!

Performance driving in mind
ST XTA coilovers feature KW damping technology which allows the suspension to be made either stiffer or softer depending on the driving conditions. This damping adjustment is made on the upper end of the chromed piston rod allowing the setup to be changed almost instantly. If the rebound force is increased, the car will drive with more track stability and reduced bodyroll. If the rebound force is decreased, the car will feel more comfortable when on the move. For increased performance, the ST XTA features an aluminum adjustable topmount allowing the camber and caster to be adjusted depending on your driving needs or vehicle setup.

Easy lowering adjustment
Like all ST coilovers the lowering adjustment is made via a continuous thread on the galvanized strut. This even allows the lowering to be made when the kit is installed by turning the spring plate higher or lower! NOTE: The lowering of each vehicle differs greatly with ST XTA coilovers due to the type of construction. For example, older vehicles such as the Honda Civic (EJ9) can be lowered between 40-75mm with ST XTA coilovers, while newer models such as the Audi S3 (8P) can be lowered between 10-40mm due to being much lower from the factory.

KW Engineering: Exclusive for ST suspension
The high-quality ST XTA coilover is based on the twin-tube damping principle of low friction combined with pressure-resistant damper housings. Manufactured directly at KW, a mono block guide and seal package reduces the friction of the damper as well as protecting it against corrosion and dirt. Each galvanized strut is sealed multiple times to ensure maximum longevity in ALL weather conditions.

• Latest damping technology for maximum longevity
• Reduced system friction for effective damping adjustment
• Individual lowering within the TUV-tested adjustment range
• Front and rear axle (when possible) with thread adjustment
• Galvanized coilover struts with additional coating for an optimized corrosion protection
• Complete solution with adjustable spring plate, race spring system and bumpers with dust protection
• Aluminum adjustable uniball top mounts (when possible)
• Scaled camber adjustment (optionally also caster)
• Externally adjustable damping

ADVANTAGES OF A ST COILOVER SPRING STRUT:

• ST Suspensions - Spring Strut Construction
• Excellent all around performance, provides a balance between performance and comfort for everyday use
• High-quality components for long durability
• Use of twin-tube technology, independent reactions from damping inputs minimized chassis vibrations and increase driving dynamics
• Coilovers come with all necessary components, vehicle-specific certificate and insallation instructions

Functional principle of twin tube shock absorbers
With a Twin-Tube shock absorber, the piston works inside of an inner Tube. The space between the inner tube and the casing is used as an equalization chamber. Changes in volume due position of the piston rod change the oil level in the equalization chamber between the outer casing and inner Tube.

Compression phase:
When the car swings downwards in the direction to the road, the piston rod is moved downwards.The oil displaced by the piston rod is pressed into the equalization chamber between the Tubes via specially designed orifices in the compression valve at the lower end of the inner Tube. The resistance that is created through this valve creates the actual compression forces. Oil underneath the piston also flows upwards through the piston check valve with low resistance which also influences the damper characteristics.

Rebound phase:
When the car swings upwards, away from the road, the shock absorber is extended. The piston rod is extending outward from the housing. The rebound phase valve at the lower Tube resists the oil that flows downwards through the holes in the space above the Tube. Therefore the upward motion is slowed down. When the piston rod is pulled out of the case, its volume is balanced out by the oil that flows from the equalization chamber back into the inner tube through the compression check valve.

Functional principle of mono tube shock absorbers
With a one-piston shock absorber, the piston works directly in the damping case. Both, traction and also compression phase valve are integrated into the piston at the end of the piston rod. Depending on the velocity with which the shock absorber is compressed or extended, the forces rise. A characteristic is the separating piston that separates the oil from the gas space which is under strong pressure. The gas space balances the oil expansion with temperature differences and volume changes while the piston rod retracts. The separating piston thereby moves upwards and downwards. The gas pressure of 25-30 bar in the separating space is necessary in order to support the damping forces in direction of the pressure direction.

Compression phase:
When the car swings downwards in the direction to the road, the piston rod is moved downwards. The compression phase valve on the top of the valve resists the oil that streams upwards through holes. Therefore, the downward movement is slowed down. The separating piston is thereby lowered by the same degree as the piston retreats downwards. The gas pressure underneath the separating piston thereby prevents the oils from foaming above the piston.

Rebound phase:
When the car swings upwards, away from the road, the shock absorber is extended. Thereby, the piston rod is moving out of the damping case. The rebound phase valve at the lower piston resists the oil that flows downwards through the holes in the space above the piston. Therefore the upward motion is slowed down. The separating piston is thereby lifted upwards by the same degree as the piston extends.