Suspension: Different Springs, MonoTube vs TwinTube Dampers

Discussion in 'Suspension / Tyres / Brakes / Wheels' started by MeisterR, Sep 17, 2012.

  1. MeisterR

    MeisterR Paid Member

    The goal of this article is to provide some general information to the enthusiast community.

    I often get ask how coilovers springs differ from lowering springs and how mono-tube dampers differ from twin-tube damper, so I decided to write this article to provide the enthusiast community with some general information on suspensions.

    Many owners install Coilovers suspension looking to enhance their vehicles looks and performance.
    While there are many different parts that make up a suspension system, the heart of the suspension is the springs and the dampers.


    So what exactly does a spring or a damper do?
    Well, at the most basic level springs control the amount the suspension moves up and down.
    The dampers control the speed at which the suspension moves.

    In driving terms, the springs control the amount of body roll, squat and dive the vehicle has.
    The dampers control the speed of those movements.
    The combination of spring rate and damping force are what determines the performance and ride quality of the suspension.


    Type of springs
    There are two basic types of springs, linear and progressive.

    A linear rate spring is one that has a fixed spring rate, this means the amount of weight, needed to compress the spring does not change with the load.

    A progressive spring is one in which the spring rate changes depending on the amount of load placed on the spring, therefore the actual spring rate is not a fixed number.


    Characteristics of Linear Springs

    [​IMG]

    Linear rate springs have a fix springs rate throughout its rate of compression, therefore the first inch of compression will require the same weight as the second inch of compression.

    Most coilovers suspension offers a straight internal diameter (ID) linear rate springs, this makes changing springs rate much easier and most springs manufacturers offer springs in a wide selection of springs rate, ID, and free length.

    The main advantage of linear springs is the consistency in the way that the weight transfer from one side of the car to the other side, it should be very smooth and consistent, this makes the cars dynamics much easier to predict as the driver can anticipate weight transfer and body roll more accurately.

    When exiting a corner, a linear spring will settle the cars body in a smooth manner because both sides of the car are compressing and rebounding at the same rate (1 mm of compression to 1 mm of rebound).
    This is a great advantage and allows for more confident use of weight transfer because the driver will not experience unpredictable weight shifts.


    Characteristics of Progressive Springs

    [​IMG]

    Progressive springs rate changes depending on the loads placed on the springs, therefore the first inch of compression will require a different amount of weight to the second inch of compression.

    Most aftermarket lowering springs are progressive springs.
    The main reason, is that the springs must be soft enough initially for the car to reduce its ride height, but hard enough at the compressed state to prevent the standard damper from bottoming out.

    When exiting a corner, a progressive spring will send the compressed force from outside of the car to the inside.
    Since the spring rate is not constant from side to side, the spring on the inside of the car will compress from the force absorbed, it will then send the compressed force back to the outside.
    This happens back and forth as the car slowly settles down. This excessive body roll requires more attention to control effectively.

    In winding road driving, progressive springs make steering more complex and demanding compared to linear springs.



    Type of Dampers
    There are two basic types of dampers used in the auto industry, Mono-Tube and Twin-Tube dampers.

    Mono-tube dampers use a single outer tube.
    A floating piston separates the oil and nitrogen gas inside the damper unit.

    Twin tube damper use an inner and outer tube which separate the oil and gas inside the damper.
    The smaller inner tube houses the piston valve & shaft assembly, base valve and oil.
    The outer tube contains both nitrogen gas and the damper oil.

    [​IMG]


    Characteristics of Mono-tube Dampers

    The main advantages of mono-tube dampers are that mono-tube pistons are much larger than those of twin-tube dampers.
    The larger mono-tube piston create more flow through the valves than the smaller twin-tube piston as it can displace more oil through the valve; this makes the mono-tube damper more sensitive to small suspension movement.

    The deflected-disc valve system found in mono-tube system is more precise and consistent than the system of check valve, springs, and orifices commonly used in twin-tube dampers.

    Mono tube dampers use much higher gas pressure also run much cooler than a twin-tube damper.
    These means mono-tube dampers are able to provide consistent damping performance under the harshest condition (such as track use).

    The main disadvantage of a mono-tube damper over a twin tube damper is the cost.
    Precision, consistency, and performance advantage mean parts used in mono-tube dampers have to be produce with higher accuracy than twin-tube dampers.
    A much more expensive, seamless-type tube are needed for the mono-tube damper casing, and precision seal are needed to contain the high internal pressure of a mono-tube damper.

    The performance advantages of the mono-tube dampers make them the choice for serious suspension tuners looking for the best possible dampers.
    Most high end suspensions from renowned suspension tuner employ mono-tube dampers, as with high performance vehicle application such as Nissan GTR, Porsche Carrera, Mitsubishi EVO MR, Subaru WRX STi, etc.


    Characteristics of Twin Tube Dampers

    The main advantage of twin-tube dampers is lower manufacturing costs.
    Twin-tube damper use much lower gas pressure than mono-tube dampers. This eliminates the need to have a highly polished piston chamber with a floating piston to separate the pressurized gas to the oil inside the damper.

    Twin-tube damper are also more durable against external damage.
    Since the internal of a twin-tube damper are located inside the inner tube, damage to the outer tube (such as dent) will not cause the damper to cease functioning.

    The main disadvantage of a twin-tube damper over the mono-tube damper is the inferior performance.
    By using smaller internal parts, twin-tube dampers provide less sensitive damping and produce higher temperature under hard use than a mono-tube damper.

    While twin-tube dampers still offer great performance, their construction limits their performance when compared to that of mono-tube dampers.
    Due to the lower cost and ease of manufacturing, twin-tube dampers are the most commonly used type of dampers by OEM (Original Equipment) manufacturer.
    Most OEM replacement dampers and low-end aftermarket suspension products are twin-tube dampers.



    With suspensions, there are alot of variance (such as some twin-tube dampers that use deflected-disc valve system) and it is impossible to cover everything.

    I try to produce this article with an unbiased view, it is up to the reader to decide what product best suit their needs, budget, and requirement.
    I hope this information is useful and should anyone have question, please feel free to contact me info@meisterr.com

    Thank you for reading and I hope to be able to assist you in the near future.

    Jerrick Lo

    Director of MeisterR Ltd.
     
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