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harris.racing

Thought I'd put together a quick post with regards to suspension kits/setups. 

 

I regularly see the same questions asked, particularly on social media with regards to suspension kits, lowering cars etc; so I thought I would try and generalise some advice.

 

Generally, the majority of people seem to want to lower their car, which can be achieved in several ways.

 

Cheapest option:

 

IMG_1603.JPG.84875e17ce2e3420dcdafb399703efe4.JPG

 

Lowering springs.

 

These can be bought cheaply, and of different brands and quality.

 

Often designed with a few of the coils designed to go coil-bound under the vehicles weight, this ensures the spring is still properly seated with the suspension in full rebound, but also allows it to sit lower under its weight.

 

Generally, you get what you pay for - the springs will tend to be a different rate to standard, and totally change the character of a car, therefore the standard dampers will no longer be matched to the rest of the vehicle. You may find it doesn't drive too great with just lowering springs, or you suffer premature wear of your dampers.

 

Spring and shock kit:

 

IMG_1604.JPG.91c76c6ac679e4c11ca2bef83e7a49e1.JPG

 

As mentioned above, damping can be an issue with lowering springs - not just the damper settings themselves, but also the range of travel the damper has - generally a lowering spring will be both shorter and stiffer, so to ensure it has the correct amount of pre-load, dampers matched to lowering springs tend to have reduced travel.

 

You can spend between £100 and probably £1500 on a spring and shock kit.

 

Cheaper kits will do the job - but probably won't be as good a quality, or have had any of the R&D which a more expensive kit will have had (Bilstein for example)

 

Dependant on your vehicle platform, ride heights can be adjustable with a spring and shock kit via a circlip on the damper body, however, not as accurately as 'coilovers' 

 

Coilovers:

 

 

IMG_1605.JPG.2b010bcfbb4b6a39a07a020b0a05170b.JPG

People commonly describe a lowering kit with threaded height adjusters as coilovers, when really coilovers just means a coil spring over the damper, so technically every standard polo has coilovers on at least the front, and on the rear on some models too.

 

However, for ease of description, coilovers are a spring and damper kit, which generally has threaded adjusters for adjusting ride heights. 

 

This is what people tend to go for to get their cars really low (although a lot of them aren't actually approved to go as low as people run them) 

 

These are great for tweaking your ride heights, and particularly if you have a track car, setting up the corner weights accurately. 

 

Again, you get what you pay for, cheap coilovers can be had for around £150 and up to and over £2000. Cheaper ones tend to again 'do the job' by lowering the car, however handling and ride quality tend to be somewhat sacrificed. More premium brands such as KW put more development into their kits, therefore you are paying towards that, but essentially end up with a better product.

 

Air Ride

 

 

IMG_1606.JPG.5188eb395e4dee1ac8f7cfd4fe39df30.JPG

I don't really have any experience with after market air suspension, so wouldn't like to comment on what is good and bad.

 

Air will let you drive your car at a sensible height, then release air from the air springs to lower your car to look better.

 

Air springs can be a very tunable component, however I have no idea how much thought is put into this for after market kits. Certainly sleeve bags can be made to have linear and non linear rates so you could essentially make a great kit if the effort was made.

 

From what I have seen a lot of kits use bellow style bags, which I don't really know anything about.

 

Air can be bought cheaply second hand, or you could pay up to £10000 getting a good kit professionally installed.

 

Summary

 

When it comes to suspension, the first thing you should ask yourself is 'What am I trying to achieve?'

 

Generally you are compromising a car from what the manufacturer originally created when you start fitting after market suspension, so you need to decide what you are willing to compromise, whether that be ride quality, handling, durability, practicality and so on.

 

Personally I would save up as much as possible to buy the best quality kit you can, it may even pay to buy a premium Spring and Shock kit, instead of a cheap coilover kit.

 

I have witnessed lots of horrors with after market suspension kits, with regards to how they are fitted, or removing parts to make cars lower etc. Just bare in mind, if things like helper springs and bump stops are supplied with a kit, they are supposed to be fitted - if the manufacturer didn't deem them necessary, they wouldn't put them in!

 

When you are driving along and the vehicle goes into a heave moment, such as a small "jump" in the road the main springs become unloaded, without helper/tender springs, the force of the spring acting on the tyre contact patch is lost, the same thing happens when cornering - as the car rolls and the inside of the car essentially lifts up, the spring becomes unloaded, this results in a huge difference in contact patch loading on the tyre, which could well result in erratic and dangerous handling characteristics. 

 

Here is an example with a tender spring correctly fitted. The vehicle has its wheel off the ground, so the damper is at its maximum rebound travel, yet the spring is still preloaded:

 

IMG_1607.JPG.dcea3f75bc1b465e6f68a42d9105c69d.JPG

 

Here is an example without a tender spring fitted, note the gap at the top of the spring, this means there is a lot less force acting on the tyre (basically just the weight of the unsprung mass hanging down) but also when the suspension is compressed again it will have very little force due to no spring resistance, and then a sudden large build up of force:

IMG_1608.JPG.364cba92dfab429dc37cec05000f9691.JPG

 

You will find with more expensive coilover kits, the height adjustment range is a lot less than that of cheaper ones, this is because it has been designed to work around a certain range, and optimised for that. This is a key indicator that cheaper kits which have a huge lowering range aren't perhaps as great as people think.

 

I have tried to explain in simple terms to help people understand, but anyway, I hope this brings some help to someone!

 

 

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