Coilovers vs springs and struts/shocks

One of the common ways to increase suspension performance and looks is by lowering your vehicle. Lowered vehicles look more aggressive and benefit from improved handling. There are different ways to achieve this, each with their own benefits and characteristics. So let’s have a look at the difference between Coilovers, replacement springs and struts or shocks. 
If you are not familiar with the term coilover it is short for coil spring over strut. Coilovers look vaguely similar to the stock suspension spring and strut setup.  A performance orientated spring and strut replacement look exactly the same as factory suspension.  While lowering springs and coilovers will both serve to make your car lower, they achieve this in different ways and provide noticeably distinct handling characteristics. With Coilovers offering additional benefits.
Some drivers are unsure on the best option to go with. Some want their car to just sit lower, while others want the ability to adjust the ride height and real enthusiasts will require the flexibility of fully adjustable coilovers with rebound and compression adjustments in addition to ride height and camber plates.
 coilover and strut
 Lowered Springs
The simple option is to replace the existing springs with lowered springs. Like factory springs, lowered springs are made to support the weight of the vehicle and fit in place of the factory spring with no modification required.
Lowered springs are physically shorter than OEM springs when installed, so the ride height of the vehicle is lower. Now since spring rate is measured in Kg per mm, a spring that’s shorter than stock will have a higher spring rate which means a firmer ride. For performance driving, this is considered a benefit. This firmer spring rate results in less body roll keeping your car flat and the lower center of mass improves your handling and stability.
Lowered springs are cost effective and offer better handling than OEM.  They are mostly compatible with existing parts meaning only the springs are replaced. However the match between shock and spring may not be perfect and the result in performance improvement may not be as decent as a coilover. No adjustments are required or possible after fitting as the spring rates are set as is the ride height. However springs are available in linear or progressive spring rates.
king lowering springs 2012 brz frs
Non Adjustable Coilovers
Non shock adjustable coilovers are an entry level option. They look the same as a coilover and come with the damper and are height adjustable. No adjustments are provided for stiffness, compression or rebound. Most will be pre-assembled and ready to install. The top mounts are without camber adjustment and included with units.  These are a good choice for those who want to lower their car, have ability to adjust the amount of lowering, and want something reliable. The price is less than fully adjustable units and often competitive with replacing both struts and springs.
Fully adjustable Coilovers
Fully adjustable coilovers replace the entire unit just like the non-adjustable units. The Performance characteristics of the damper and spring are matched to provide maximum performance and unlike lowering springs, coilovers offer a much greater range of adjustability including ride height, spring pre-load, shock damping and rebound. Camber adjustment is also possible with camber tops when fitted.  High-end coilover kits are lighter than the factory components reducing unsprung weight to further increase handling.
These fully adjustable coilovers allow you to fine-tune suspension settings for each corner independently for the ultimate in vehicle balance and control. Typically a coilover set features spring rates set for the vehicle weight. It is possible however to swap to springs with different spring rates for an even greater range of adjustment and tuning. 
Summing up the advantages of coilovers over strut and springs are adjustable ride height and the higher spec units offering adjustable dampening and rebound and the ability to change springs to fine tune spring rates combined with lighter assemble reducing unsprung weight. Top end units will also be fully serviceable.
Coilovers designed for hard use like Rally or off road will have remote canisters which increase fluid capacity to aid cooling to prevent aeration.
MCA gold
How are coil overs adjusted?
There are two basic ways coilovers are manufactured to allow ride height adjustment. In one system the spring seat is moved to compress the spring against the top hat which lowers the vehicle. The fault with this system is you are changing pre-load on your springs which will adversely affect handling. The preferred method is where the manufacturer has threaded the actual shock body to allow the base mount to be lowered or raised. This doesn't affect the compression of the spring and is the preferred way to adjust the height. C Spanners are used to perform the adjustment.
c spanner
Performance and cost
Racked from a performance perspective. Cost is indicated by ($)
Lowered springs with stock shocks are the cheapest option. ($)
Lowered springs with performance shocks come in second.  ($$)
Lowered springs with performance adjustable shocks ($$$) Cost Vs performance does not add up for this option.
Sleeve type coilovers and non-adjustable shocks ($$) 
Sleeve Type Coilovers with Performance Adjustable Shocks ($$$)
Full body nonadjustable ($$$)
Full Body Coilover fully adjustable Kit ($$$-$$$$)
In reality the only downside of fully adjustable coilovers is cost and set up time.

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