Understanding Coilovers and How to Get the Best Performance Results.
Updated: Jun 1, 2019
Despite initial appearances, not all Coilovers that may be available for your performance car are of the same quality, nor will they all offer the same performance.
The worst quality will tend to corrode most easily or begin to leak or rattle within as little as a few months of being fitted. As the old saying goes, buy right and buy once: It's better to spend more for a quality brand that offers good after-sales service than cheap offers found on eBay and such-like.
Remember many brand recommendations you see on forums, FB chats, etc. are from people who have very limited experience.
In our case, here at Newera Imports, we've not only experienced every Japanese Coilover brand in the thousands of cars we've supplied over two decades, but have also chosen the best brands to use on our own cars and even had bespoke coilovers built for specific road & race applications.
Like most experienced enthusiasts, we avoid compromising as much as possible, so our preferred choices for our own vehicles have included Nitron, Ohlins, Bilstein & Aragosta to name a few of the brands we've had the best results with, and for more road-based applications have had good results with Apexi N1 & Nismo Struts & Bilstein sports shocks too.
We've avoided well-known brands such as HKS Hypermax, or TEIN because we've had to replace so many of these as part of preparation work on cars that Newera has supplied for sale.
We'd rate TEIN as low in quality as some of the S.E. Asian manufactured brands, as they've too often been found to have fluid leaks, pillow ball rattles and other quality issues, as well as poor after-sales backup, despite being a Japanese brand.
As our example on this occasion, we've chosen to showcase Nitron, which would be our first choice where budget isn't the main constraint.
Nitron is a company specialising only in the manufacture of performance suspension, both for motorcycle and car applications and they have an especially large following for Motorcycle racing applications.
In this example, fitted to a Skyline GT-R, their coilovers offer all of the desirable qualities, such as:
Independent Height Adjustment (Useful for corner weighting), Separate Bump & Rebound setting adjustments, helper springs and main springs, Remote oil Reservoir & high-quality precision-made components.
When specifying coilovers, Nitron asks each customer not only what the vehicle's intended use will be, but what sort of tyres, weight and surfaces it'll be driven on. Naturally, a car that will be driven on bumpy country roads with up to 5 occupants and on street tyres in all weather conditions, will need softer springs and correspondingly different damper settings than the same model of car, stripped out, with a lot more power, being driven on smooth circuit surfaces, using slick tyres - in a much higher speed racing environment.
For this particular customer's Skyline R32 GT-R, the setup specified is for fast road use, but not for intended for circuit or racing.
Spring rates were therefore set accordingly by Nitron during bespoke manufacture. As the Skyline GT-R carries most of its weight at the front, it follows that spring rates are harder at the front than at the rear (As would be the case with most coilover brands for a 32 GT-R).
The harder the spring rate, the firmer the suspension will naturally feel. Too soft and the coilovers will bottom out on some bumps, possibly leading to damaged oil seals. Too hard and the car will tend to jump over bumps rather than absorb them.
I won't specify what rates were used for this particular case, to avoid misleading the reader, but rates and spring length are an important aspect that changes with suspension design & car model, plus intended use.
Suffice to say, Nismo's spring rates for their S-Tune Suspension kits are roughly half of what some coilover manufacturers offer for track-day suited coilover kits; both of which are road legal.
We see many enthusiasts wanting to run their cars as low as possible, with coilovers set as low as they can get away with. Whilst a low stance can look cool, it doesn't necessarily make the best use of a car's design geometry.
Running too low can lead to accelerated inner tyre wear resulting from excessive camber and can also contribute to other problems such as premature wear of suspension components.
Older Hondas are one example where we see many being run extremely low. This can lead to damaged exhaust manifolds, which can restrict exhaust flow, or lead to other damaged underside components, or dented chassis rails, broken front bumper splitters, damaged wheel arches, etc.
Some will remove inner plastic arches (Which can lead to water leakage and other problems), roll their fender edges, etc. but remember - other problems such as much reduced tyre life can result.
In our case, for road-cars, we tend to drop ride by no more than around 20-25mm, but its a matter of preference, if not compromises.
Damping: Keep it to a minimum.
Damping is often misunderstood. By understanding this important point, you can avoid the pitfalls:
A vehicle's suspension is meant to absorb a bump, such that the car body's oscillation vertically over a given bump is kept to an absolute minimum.
As the front wheel goes over a bump, the suspension should compress and then drop quickly as the tyre begins to drop off the summit of the bump.
The rear wheel naturally goes over the same bump and ideally, it should be set so the suspension travel and speed of damping response is the same.
Where the suspension is set right, pitching over bumps should be at an absolute minimum.
We see many people talk about "firming up" their suspension by adjustment of damping. Actually, what they are often doing unwittingly is increasing damping so much that the shock absorber becomes "lazy".
In such case, the spring's work is reduced, as now the damper's travel is so slow that the spring's work is reduced.
Instead of the coilover assembly correctly absorbing a bump, it's resistance has been increased so much that the wheel no longer travels over the contour of the bump, with suspension neatly "absorbing" the undulation. Instead, the car pitches or even jumps over the bump with minimised suspension travel. Worse, as the car comes down the bump, the rebound damping may now be so over-applied, that the spring cannot cause extension of the coilover fast enough and the tyre momentarily loses some of its available grip. When measuring the difference on a circuit, this can amount to a loss of as much as a second a lap or more. Although very firm damping feels faster, it's usually not.
Where damping is set too soft, the oscillation from a damper isn't stopped, so the car tends to wallow over bumps, for example. Where there's been fluid leakage and no damping exists at all, then a bouncing can occur over bumps, which is undesirable, but might help to imagine the results of too little damping.
So for road use, as an example - the best thing is to start with too little and gradually increase damping to where it's most comfortable and the car pitches the least. Usually left to right settings are the same but rear settings may be less than forward if the front is where most of the car's weight is carried.
Remember also, that the faster a car is travelling, the more kinetic energy the dampers and springs have to deal with; travel over a given bump becomes more violent.
So for such applications, if spring rate isn't enough - then the shock absorber may bottom out. You can increase damping a bit, but this isn't the way to fix the problem.
The professional way to increase firmness and avoid bottoming-out is to increase the spring rate. This is where increased damping is then called for since the spring then stores more kinetic energy.
To help give some understanding, the way coilover damping works is by having fluid travel past shims with small holes, which are sometimes referred to as "valves". By changing the valving characteristics (such as moving shims closer or further apart), fluid can travel faster or slower past these shims. In better designs, the fluids are pumped through a system of an inner and outer cylinder (Bilstein and Ohlins have patented such systems for example), so that heat created by fluid friction can be dissipated during travel (The hotter the fluid, the less the viscosity - this is why you'll find the higher quality coilover kits offer remote fluid reservoirs).
As part of maintenance, it helps to also keep coilover moving parts lubricated. Pillow upper mounts can wear (this is where choosing brands that offer good after-sales service, also counts), especially when not lubricated, but ride height adjustment, etc. can seize if not cared for. Copper grease can be useful to help stop seizure if applied when fitting new coilovers.
In our experience, it's best to avoid the use of Poly Eurethane bushes, where spherical bearings or conventional rubber bushes are available. Poly bushes can disintegrate in alarmingly short spaces of time.