To achieve the best lap / stage your cars wheels and tyres need to be in contact with the track or stage as much as possible. The springs need to be strong enough to support the weight of the car and can also play a role in reducing roll and weight transfer (combined with the anti-roll bar, more so if the model does not have one fitted). The damping needs to control the movement of the spring to allow the suspension to respond quickly to the changing track surface. Suspension choice can be rather complicated, but if the best choice is made it can turn your vehicle into a front runner. Continue reading this competition suspension guide to make the choice a little simpler.
Before deciding on the suspension set up to use it is best to check the regulations for your championship, some specify the type of damper and spring, even the brand if you compete in a one-make championship. The various elements of suspension rules to check are below :
Check the rules state if the damping must be fixed, or is adjustable allowed, if adjustable does it have to be single adjustment or can double / triple adjustable be used. It is worth checking if the rules state if piston rod size must be standard and if gas pressurised dampers are allowed. Some rules will not allow remote reservoir units. For those not familiar with suspension terms :
This means the compression and rebound strength / damping is not adjustable at all. ( compression is the suspension being pushed upwards, rebound is when it extends away from the car ) The damping can be as the factory setting or uprated but there is no means of altering the settings.
Single adjustable damping
Single adjustable dampers allow the compression and rebound to be adjusted at the same time so both will increase in strength proportionally. This can be at the top of the damper piston rod on strut type units or at the bottom on bolt on dampers.
Double adjustable damping
Double adjustable dampers ( sometimes known as 2-way damping ) have separate adjustment for compression and rebound. This allows the damping to be fine tuned to the track or driving style
Triple adjustable damping
Triple adjustable / 3-way damping has two settings for slow and high-speed compression damping and another adjustment for rebound
Four-way adjustable damping
Not so common but both compression and rebound damping have low and high-speed settings.
Mono Tube / Twin Tube
Mono tube is the generally preferred choice for Motorsport use, the damper has the oil and valving pressurised by a free-floating piston, so it is always ready to provide damping. The body is a single tube so the piston and valving can be bigger than the twin tube. The single tube also allows better cooling as the oil is closer to cooling air much reducing the chance of fading. Twin tube dampers have the valving and piston in the centre of the unit with the oil reservoir on the outside, some have gas pressure or inert gas to help reduce fade and air bubbles forming. These can work very well especially adjustable units and tend to be more cost effective and more widely available than mono tube.
This is a separate chamber either piggy backed or connected by piping to the main damper body. This allows more damping oil to be used to allow better cooling and can house adjusters.
If the damper has a spring seat the rules might state to use standard platforms to take stock or uprated and lowered springs that fit the factory fitted suspension. Some rules may allow adjustable height units to be used, in other words the spring seat sits on threads so the ride height can be changed.
The type of spring will be specified, this could be the factory fitted spring, or spring that fits in the stock position but allows free rate or length, or if adjustable platform dampers are allowed may allow use of coil over springs, that can be had in most free lengths and rates.
The rules may state to use the factory fitted. If uprated bars are allowed these can be larger diameter for increased roll control and some are adjustable in stiffness.
The bushes may be stated same as fitted as standard, if they are free then uprated polyurethane versions will give much better location, and some can adjusted to change geometry to make more suitable for competition use.
Mounts / control arms
if the rules allow changing mounts for uprated types this will allow better positive suspension location. Again, if suspensions / control arms can be changed for adjustable types of the car can be made much more suitable to motorsport use by fine tuning castor and camber settings.
Fixed Damper Choices:
The B4, B6, B8 dampers are on offer with Bilstein. The B4 is gas pressurised and slightly uprated to compensate for any wear. This can be used as a stock replacement damper if the rules allow the brand. The B6 is mono tube damper that has high pressure gas to make sure the valving is always in the damping oil to give very positive almost instant damping. Mono tube dampers also allow the oil to cool quicker to resist fade. Most units have a larger diameter piston rod which helps the damper resist side loads much better than standard sizes. The B8 is very similar to the B6 but has a shortened piston rod to suit lowered springs. Bilstein also offer motorsport specific dampers for popular motorsport cars, these are fixed but have quoted bump and rebound strengths listed
The STR.T is uprated and a very quick reacting unit but designed to work with standard or uprated springs, and will work with lowered springs up to around 40mm lower.
KYB Supply many of the Japanese car manufacturers with OE dampers. They offer fixed rate dampers; most are twin tube Excel G which are slightly uprated. Ideal replacements for worn out units. Some applications have the choice of Gas A Just which is 30% stronger damping and mono tube construction and others applications the Ultra SR, which is uprated above the Excel G and is aimed at harder use.
Adjustable damper choices:
AVO have a range of single adjustable twin tube gas pressurised dampers, these are all adjustable on the car, either at the top of the unit or at the base by the bottom mount depending on the design. AVO also offer a range of universal telescopic dampers with poly bushed eyelets or spherical bearing ends, available in single or double damping adjustment in a selection of open and closed lengths. There is also a choice steel or alloy bodies These are ideal for rare / unusual or classic cars where nothing is listed, or for conversions to replace lever arms or friction dampers etc.
The Sport units from Koni are single adjustable, some adjustable on the car, some adjustable off the car. The dampers can be twin tube or mono tube depending on the application. Classic as the name suggest covers older vehicles. These are mostly adjustable off the car and twin tube design, a big improvement over the originals. 4×4 are covered by the HT Raid range, adjustable off the car, big bore damper body for increased oil capacity and cooling.
Spring Choice for Standard Platforms:
If the rules dictate the springs fit the standard spring seats but rate and ride height can be changed. A lowering spring set will lower the centre of gravity, reducing squat during acceleration, body roll in corners and excessive nosedive under braking and can be bought for most models. The following brands are available.
A popular name in performance springs are Eibach. They offer two spring kits. The Pro-Kit lowers around 25-30mm on most models and the progressive springs mean they increase in rate as they compress and are much more resistant to bottoming out than straight springs. Some models have the option of Sportline springs which are lower and higher spring rate than the Pro-Kit
H&R offer their Sport spring kit. This lowers 25-40mm depending on the application. The springs are progressive or linear again depending on application.
German spring maker Vogtland have their Sport spring kits which lower 25-40mm depending on the fitment. Good quality lowering springs at a lower price than the above brands.
Adjustable height and damping coilover kits:
If the rules allow a ride height and adjustable damping a coil over suspension kit will allow the suspension to be fine tuned for the intended use, the options are as follows :
AVO list a selection of kits to cover most budgets. GTZ are single adjustable with twin tube dampers and primarily aimed at road and track day use but very cost effective. The RT kit is a step above the GTZ and includes bearing top mounts in most applications, and struts are 40mm mono tube piston rod type. Again, this is aimed at track day use but is lower cost than the pure motorsport kits.
The following are AVO’s kit intended for race / rally. The R1 kit is single adjustable, fronts are 40mm inverted mono tubes and rears can be mono tube or twin tube depending on the application. This kit is intended for race or rally use. The R2 kit is as above but bump / rebound can be adjusted separately again this is intended for race or rally use the double adjustment allow fine tuning. The R3 kit uses two- or three-way mono tube dampers with remote reservoirs and gives the ultimate set up. Avo can supply springs to suit race or rally on all their R kits and can either advise on the best set up for the intended use. Alternatively, they can supply to your own specifications if you have a specific set up in mind.
Offerings from BC Racing are the BR, RM, ER, HM, and ZR, kits, which fit a very comprehensive range of cars. Their kits have height adjustment which is independent of spring compression, so the height can be adjusted without losing travel. The BR kit is single adjustable, and damping has 30 settings, some with adjustable top mounts depending on the application. The RM kit uses monotube dampers with 30 settings and most come with adjustable top mounts. The ER series has two-way adjustable dampers and remote reservoirs, the extra oil capacity helping cooling the adjustable top mounts on most kits. The HM series has mono tube dampers but with separate bump and rebound adjustments, again most have adjustable top mounts.
The ultimate kit is the ZR series, this has three-way adjustable damping which offers 30 clicks of rebound adjustment, 15 clicks of low-speed compression adjustment, and 12 clicks of high-speed compression. Front and rear camber plates are standard on all applicable Kits or Pillowball mounts are standard when camber plates are not possible.
Bilstein offer the Clubsport kit which is aimed at trackday and club racers. These are double adjustable with ten clicks each via red adjusters for rebound and blue for bump. Camber adjustable top mounts are supplied.
The GAZ Gold coil over kits are single adjustable dampers which are adjustable with an external knob. These come with 62mm bodies and large 22mm piston rods for increased strength. The Gold range covers a lot of older models not listed by other brands.
The NTR-R1 Nitron kit is double adjustable with 24 click adjustments. They have alloy bodies which have less weight and better cooling. The top specification kit is the NTR-R3 kit which has remote or piggy-back reservoir and three-way adjustment. High speed compression has 16 clicks, low speed has 26, and rebound has 24 clicks.
The Ohlins Road And Track kits offer premium quality combined with either DFV or TTX valving. Bump and rebound adjustable separately.
The kits offered by Tein are aimed at specific disciplines. The Super Racing kit is mono tube construction, bump and rebound with 16 settings can be set individually. Camber adjustable top mount or Pillowball mounts depending on the applications. This kit is aimed at circuit use. The HG Rally kit is aimed at rallying or rough terrain use as the name suggests. This kit is double adjustable and has steel bodies for strength. These kits can be run at stock ride height or slightly lower or higher if required.
Older / classic cars with struts and removeable inserts can be converted using weld on threaded tubes, very useful if no uprated springs or suspension kits are available.
Replacement coilover springs are available in a vast selection of lengths, ratings and internal diameters from Faulkner, Eibach, and Tein.
A stiffer anti roll bar will control roll without upping the spring rate, meaning the suspension can be more compliant, which can follow the track surface better. A stiffer bar can also alter the balance front and rear to help turn in and fine tune under or over steer. A front wheel drive car will have reduced understeer with a stiffer rear bar, generally the same for a four-wheel drive car. Rear wheel drive will benefit from a stiffer front bar. Most production cars have a small bar size to give neutral handling so most will benefit going bigger front and rear, kits are sized to change the balance front to rear to suit the application. Some bars have adjustable mounts to further fine tune the handling.
Eibach offer a good selection of anti-roll bar kits very good range for VAG group cars.
H&R list probably list the largest range of bars for European cars.
Hardrace specialise in Far Eastern models and offer front and rear kits.
Superpro have a range covering mostly VAG group cars.
Ultra Racing cover both European and Far Eastern brands, often the less common cars. Front and rear bars for many applications.
Whiteline are perhaps the best known supplier of anti-roll bars, many models have a choice of size and fixed or adjustable.
Replacement bushes in polyurethane will locate suspension components much better and stop unwanted geometry changes, allowing to place the car better on the corners. Some kits allow changes in caster or camber to allow adjustment from the factory setting.
Powerflex offer probably the largest range of vehicles. They have the purple range which is firmer than standard but has reasonable compliance, and the black range which is aimed at motorsport use. Some of these bushes allow adjustments to caster or camber often where there is no adjustment as standard.
Another brand is Hardrace. They list harder Hyper rubber bushes, pillowball mounts for suspension bushes depending on the application, and stiffer mounts for subframes. Hardrace offer a very comprehensive range for Japanese and Korean cars.
Superpro have a selection of uprated polyurethane bushes, some are supplied as a replacement arm with bushes already fitted.
This brand offers a small selection of harder rubber suspension bushes.
Whiteline cover a wide selection of European and Far East models, bushes are polyurethane and some alter stock settings or allow adjustment.
Mounts / Control Arms:
Adjustable control arms and suspension mounts will allow adjustments to fine tune the handling for competition where there is either no adjustment or a limited range as standard. Brands that offer suitable parts are below :
GRP4 cover Ford Escort Mk1/2 top mounts several types available.
Rix have universal concentric or eccentric top mounts, easily machined to fit almost anything that has top mounts.
Superpro have a range of arms for mostly VAG group cars.
Whiteline list a very wide selection of adjustable arms, and mounts .
Cars with front or rear struts with two bottom retaining bolts can use camber bolt kits to allow camber adjustment, we list a selection of brands in all common sizes.
A production car with uprated suspension will always benefit from strut / body braces which will allow the suspension to work hard without flex from the body changing the geometry. These are available from BAF Motorsport OMP & Ultra Racing
Suspension Single Seater / Kit Car / One Offs / Autograss
If you have a single seater or monocoque racing car, kit car, Autograss car, or a car where you have made your own suspension set up, you are likely to need to buy dampers with open and closed length to suit your application. Dampers to suit are typically (but not always) an eyelet on both ends and will accept flat ground race springs. The springs are available in a vast range of lengths and ratings. If you are replacing existing dampers, they may have numbers on them that you can use to identify them. If there are no markings, you will need to know the following:
- Extended Length, centre to centre of bush / bearing or if stem type to the centre of the two bushes
- Compressed Length, measured as above
- Internal Diameter of bush or bearing (width / depth of bush is worth checking to)
- Spring internal diameter & free length
If you are buying to suit a bespoke suspension set up, we would recommend taking the suspension to full extension and full compression. It is recommended adding 1” / 25mm to the extended length and subtract 1” / 25mm from the compressed length. This will prevent the damper topping out (pulling at full extension) or bottoming out in use. The bushes or bearings are normally ½” bore but some can be ordered in different sizes. The units available are below:
Avo offer a range of twin tube dampers in alloy or steel, single or double adjustable, available with bearing or bushes. Great value. They also offer the same without spring platforms for cars with torsion bars or separate springs
We can order other brands so if you don’t see what you need, please contact us
Race springs are available in a vast selection of lengths, ratings and internal diameters from Faulkner, Eibach, and Tein.
We could carry on with lots more information as this is a very involved subject, but we hope the above helps narrow down the basic options. We are happy to answer questions on anything suspension related by phone or e-mail. Demon Tweeks was founded on selling suspension. We will always do our best to assist.
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