Coilovers: Tech, Buyer Guide & Brand List

[DreadAngel]

Coilovers: Advanced

Now that you know some coilover basics, let's check out the more varied features that coilovers can come with and the science behind them.

Coilover Features

• Damper Type - There are two types of dampers:
  
  
  Credits - Tein
  
  
  
  • Twin-tube - Hydraulic & Low Pressure Gas - [LHS of Pic]
    
    
    • Construct - Twin-tube refers to a shock absorber that contains two cylinders: inner and outer. The piston valve that displaces the fluid is located in the inner cylinder.
      
      
    • Advantages
      
      • Suspension Stroke - Twin-tube stroke length is along the entire body of the shock absorber, whilst the monotube's is shorter because the oil and gas chambers are stacked on top of each other.
        
      • Comfort [Due to gas] - Using low pressure gas allows twin-tubes to absorb shock better, resulting in greater comfort.
        
      • Durability [Due to gas] - Low pressure gas also means less pressure is forced against the seal so there is less friction, which allows it to last longer.
        
      • Cost - Twin-tubes are invariably cheaper to make than monotubes because of their components, design and manufacturing process
      
      
    • Disadvantages
      
      • Lack of fluid capacity - As the twin chambers take up more space inside the shell casing, twin-tubes contain less fluid than monotubes, reducing their ability to maintain consistent performance for long durations.
        
      • No Precision Dampening [Due to gas] - The twin chamber design means a smaller piston is required; therefore a twin-tube typically can not provide as precise dampening as a monotube.
        
      • Aeration [Due to gas] - The entire unit is under high stress because both the fluid and gas chambers are not separated. The combination of the rapidly moving piston, fluid and valve creates friction. If the fluid is forced through the value at a sufficiently high speed, this forms air bubbles in the fluid behind the piston, which is called aeration. This can lead to foaming that results in the shock absorber not dampening properly.
      
      
    • Suitable Application - Street (and Track for high quality twin-tubes)
    
    
  • Monotube/Inverted Monotube - [RHS of Pic]
    
    
    • Construct - Unlike the twin-tube, all of the shell casing's interior acts as the cylinder.
      
      
    • Advantages
      
      • Consistent level of dampening - The monotube design has a greater fluid capacity, allowing for increased heat dissipation and therefore more consistent performance.
      • Precision Dampening - Monotubes can run a larger piston due to their single cylinder design. This allows for a wider distribution of pressure that enhances the shock's precision.
      • No Aeration - Both the fluid and gas are completely separate so there is no aeration to hinder dampening consistency.
      
      
    • Disadvantages
      
      • Lack of Stroke/Bottom Out - As the oil and gas chambers are placed on top of each other, a monotube typically has issues with maintaining sufficient stroke. This makes it more prone to bottoming out.
      • Stiffness [Due to gas] - Monotubes by nature require high pressure gas in the gas chamber. This impairs shock absorption ability, making them comparatively stiffer than twin-tubes.
      • Durability [Due to gas] - As mentioned above, the requiring high pressure gas also leads to accelerated seal wear, thus causing increased internal friction that leads to premature failure.
      • Durability [Due to inverted design] - Unique to inverted monotubes, their complex design and additional moving parts means more things can fail.
      • Damage Resistance - The internals of the shock absorber are placed very close to the shell casing; so if the shell casing is damaged, it will also damage the internals.
      
      
    • Suitable Application - Circuit and Street [High quality coilovers can provide sufficient dampening and stroke]
    
    
  • Threaded Type - There are 2 types:
    
    
    • Traditional/Partially Threaded - Not as common but still found on some basic coilovers. Traditional threaded or partially threaded coilovers have a threaded section which does not run along the entire length of the shock body. This means that when adjusting height, the lower spring seat is adjusted and not the lock nut. The result is this:
      
      
      Credits - Cusco/JDM Option
      
      Improper height adjustment will mean that the spring will be loose and therefore lose damper stroke, resulting in the car hitting the bump stops or "bottoming out"; making the car uncomfortable.
      
      
    • Fully Threaded - Fully Threaded Coilovers have thread that runs along the whole length of the shock body. When adjusting the height, the lock nut is adjusted and not the lower spring seat. Damper stroke is retained as the springs remain unchanged and in place. This picture illustrates the height adjustment process:
      
      
      Credits - Cusco/JDM Option
      
      Preserving damper stroke minimises the chances of bottoming out and retains comfort.
    
    
    
  • Damper Adjustable - The most basic coilovers are usually non-damper adjustable; they're pre-tuned from the factory. On the other hand, the compression and/or rebound settings of adjustable dampers can be changed using a knob. Simply put, this allows you to adjust the 'damper force' or 'stiffness' of the coilovers. Different types of damper adjustability available are:
    
    
    • One-Way Adjustable Damper - Controls only compression or only rebound or combines compression and rebound. This setup is normally found on low-end coilovers and is the most user-friendly.
      
    • Two-Way Adjustable Damper - Controls compression and rebound independently. Allows for finer tuning of coilovers and is usually found on entry-level competition coilovers.
      
    • Three-Way Adjustable Damper - Controls compression and rebound independently, but one has a high/low speed setting (usually compression). You will find these on professional competition coilovers and the Hi/Lo speed adjustment on the remote/piggyback canister/reservoir.
      
    • Four-Way Adjustable Damper - Controls compression and rebound independently; both have high speed and low speed settings. As above, found on the most expensive coilovers.
    
    
  • Damper Valving - Something that is often disregarded is the damper's valving. A damper's valving is its ability to control compression and rebound during all conditions. It's what makes some setups beautiful on smooth tarmac while being absolutely nerve-racking on the street. A shock absorber with good valving will compress and rebound in a way that gives the driver confidence; it will not behave erratically or harshly when pushed but it will absorb the force to allow the driver to retain control and push on. Different types of damper valving available are:
    
    
    • Linear - Linear, as the name implies, means that the shock absorber's dampening force increases at a linear rate as the piston speed increases. This is the most common valving found on coilovers.
      
    • Progressive - Progressive at low piston speed has softer dampening force but this increases at high piston speed.
      
    • Digressive - Digressive is the opposite of progressive in that it has harder dampening force at low piston speed but decreases at high piston speed. This is generally used in high-end coilovers.
    
    
    N.B. This is purely a comparison of each type at extremes and their general behaviour.
    
    For example, when you ride a bump, a linear valved coilover will react with equal force. A progressive valved coilover will suddenly stiffen while a digressive valved coilover will soften the blow.
    
    
  • Spring Rate - Spring rate is basically how stiff the springs are in the coilovers. You can tell a lot from simply comparing the spring rate of the coilovers to other benchmarks like other coilovers of the same application.
    
    Spring rate is read like this: a 2kg/mm spring means that to make the spring compress 1mm, a load of 2kg needs to be applied. In the context of cars, this example is a very soft spring and usually found on base econoboxes where ride and comfort are key.
    
    Stiffness is not universal however; it is determined by your car's weight, suspension layout and application. The heavier the car is, the higher the spring rate needs to be to counteract its weight. Similarly cars with double-wishbone (Pre-2000 Civics/Integras, Preludes, S2000, Accord Euro, etc.) can run higher spring rates without experiencing the harshness felt by those running Macpherson (Post-2000 Civic/Integras, etc.). Application plays a key part too; in general street cars should run more conservative spring rates than those of track cars to account for unpredictable surfaces and conditions.
    
    
  • Active/Variable Dampers - The latest innovation in suspension technology is the active/variable dampers as seen in some of the latest cars from Ferrari and Nissan, which are slowly becoming available in aftermarket parts. These dampers, as their name suggests, actively alter the dampening to suit driving conditions. They are typically smooth and comfortable but firm when needed.