why base height Adjustable Shocks are Flawed

One of the biggest, most polarising differences between MCA Suspension and other suspension brands that are around our price point is that we set specific and correct wheel travel ranges using the adjustable bottom mount position and then adjust the ride height by the spring seat.

For whatever reason, most suspension products around our price point use a “base height” method of height adjustment. We have no idea how this method of design and adjustment came into existence however, we can only assume that it was due to a decision to make cheap/affordable adjustable suspension (when previously nothing like this existed) but without spending the time to gain the knowledge and understanding required.

Below we’ll demonstrate the issues associated with the base height adjustment method and why the spring seat adjustment method is the correct form of height adjustment. We’ve tried to keep the explanation brief, but have provided some more detailed information via the “Read More” buttons if you’re interested to learn more.

Base height adjustment demo.

What is base height adjustment?

In summary: base height adjustment is an incorrect form of height adjustment that is suggested by most cheaper/more affordable suspension brands and is shrouded in misinformation.

Base height adjustment is how most cheaper/more affordable brands of aftermarket adjustable suspension tell you to adjust the ride height of your car. These brands say that to adjust the height of your car you are to shorten or lengthen the shock absorber by moving the bottom mount (base) position. There are two main suggested benefits of this method which are listed below.

The spring preload can be set and stays the same no matter the ride height.
The compression and extension travel of the suspension stays the same no matter the ride height.

Whilst both of these statements are true, the idea that these things provide any benefit at all is false and in fact, can cause some fairly serious problems.

Why is keeping the same travel no matter the ride height bad?

In Summary: As your ride height is changed, the amount of room your car’s suspension/tyre has to move upwards changes also. It doesn’t make sense for a shockabsorber to have more or less travel than the car can fit at a certain ride height. A shockabsorbers travel range should match that of the vehicle’s suspension design/limitations at all ride heights.

When adjusting the vehicle’s ride height from the base (also known as the bottom mount) the coilover keeps the same compression and extension travel, no matter what ride height you set the car to. This is often mentioned as a positive thing, a selling point even, however, it’s actually a huge negative. In reality, the amount of compression travel the shockabsorber has should match the amount of compression travel your vehicle can physically fit.

If a shockabsorber has more compression travel than the car can fit at a certain ride height, there are a number of serious and potentially damaging things that can happen as a result of that:

Tyre contacting body/chassis
Suspension arm or suspension component contacting the chassis
Ball joint reaching maximum articulation
The brake line being stretched tight

Any of these things could cause damage and instability to your vehicle due to sudden contact with other components or sudden, undamped stops in suspension travel.

Alternatively, a shockabsorber that has less compression travel than a car is able to fit, is missing out on compression travel that it could be being benefitting from. For example, the car could be sitting at a near factory ride height, but only have as much compression travel as a significantly lowered car. Generally speaking, you always want as much compression travel as you can get, as it leads to improved ride quality, improved grip, improved performance and improved stability.

Whilst it’s true that there could be a particular ride height that may be perfectly matched to the base height adjusted shockabsorber’s compression travel, the problem is that you won’t really know what the ride height is, and even if you do, the chances of it being the ride height you want to set your car to aren’t great.

The tyre contacts the chassis before the shockabsorber stops the travel. Meaning the tyre can travel further and cause damage. In this example, we are showing the tyre contacting, but depending on the vehicle there can be other issues like suspension arms hitting, brake lines snapping, etc.

Shockabsorber stops the wheel before the wheel contacts the chassis however, this happens too soon which results in wasted wheel travel that could be used to provide improved ride quality, stability and control.

So how does MCA Suspension do it better?

In Summary: We set the vehicle’s suspension travel to an optimal and safe range via the bottom mount position, then the vehicle’s ride height is adjusted within this travel range via the spring seat.

As you lower the car’s ride height, compression travel will be reduced which is matched to the reduced tyre to fender gap, and as you raise the car compression travel will be increased which is matched to the increased tyre to fender gap. This way you will always have the correct amount of suspension travel, no matter the ride height.

The first thing we do when looking to design a suspension package for a new vehicle is determine the limiting factor for the vehicle’s compression travel, as obviously a tyre can’t travel upwards forever, something will hit something at some point.

The limiting factor for compression travel can be a number of things:

Tyre contacting body/chassis
Suspension arm or suspension component contacting the chassis
Ball joint reaching maximum articulation
The brake line being stretched tight

Once we’ve determined what that limiting factor is, we note the length of the shockabsorber at this limit and set the fully compressed length of our shockabsorber to that same measurement. This way the shockabsorber will fully compress (bottom out) and stop the vehicle’s tyre/suspension from travelling any further upwards past this limit, giving the vehicle the maximum safe suspension travel, no more and no less.

The vehicle’s tyre/suspension travel range is adjusted via the adjustable bottom mount of the shockabsorber. So we set the correct length of the shockabsorber by pre-setting the bottom mount position. The vehicle’s ride height is then adjusted to a position within that safe travel range by the adjustable spring seat.

Why can't the spring seat height adjustment method be used on any product?

In Summary: the spring seat height adjustment method can only be used when the correct travel range is already set. By definition, this hasn’t been done on products that suggest using base height adjustment.

The Spring Seat Height Adjustment method relies on the vehicle’s suspension travel range to be set up correctly first. If the travel range isn’t set correctly then the same base height adjustment risks are present.

Most of the time suspension products that are designed around base height adjustment can’t be adjusted to physically achieve the correct travel range due to incorrect shaft lengths or damper body lengths.

It’s only because we, at MCA Suspension, have completed a more thorough initial design process with the spring seat height adjustment method in mind, that our products feature the correct travel range out of the box.

Spring Preload Myth

In Summary: preloading a spring makes no difference to the handling or ride quality of vehicles because the vehicle’s weight always compresses it the same amount no matter if it’s preloaded or not.

Because our suspension is designed to have the ride height adjusted by the spring seat, we often get questions about spring preload.

Thanks to the spread of misinformation it’s commonly thought that preloading a spring makes the suspension stiffer, however, this is simply not true. A spring’s “stiffness” is referred to as its Spring Rate. A spring rate is represented as a measurement of kg/mm, lb/inch, etc. We’ll stick to kg/mm for simplicity. A 10kg/mm spring means that for every 10kg, the spring compresses 1mm.

So if the corner of a vehicle weighs 400kg, the 10kg/mm spring will compress 40mm. Even if the spring was preloaded 10mm, it would still compress the extra 30mm under the vehicle’s weight. So this shows that the preload makes no difference to the handling or ride quality as the vehicle’s weight always compresses the spring to the same point, no matter what preload.