Modifying Suspension


We can modify aspects of our cars suspension so that we can increase the tyre’s grip on the track during acceleration, braking and cornering and to control weight transfer during these phases to. An increase in grip will reduce braking distances and raise cornering speed. The car spends more time accelerating than braking hence overall speed increases and lap times reduce.

Let us first consider tyre grip. Your OE suspension will be set to maintain a compliant ride (that caters for a wide spread of customer requirements), safety (most cars are set up to understeer at the limit of tyre grip) and economy (both in terms of fuel economy and component wear such as bushes, tyres, bearings etc.

In the first instance for a track car build we want a lower ride height to reduce the cars weight centre and a stiffer spring set to control body roll and weight transfer. Ideally we want to build in some adjustability into the suspension geometry to increase the tyre contact patch with the track and some adjustability into the dampers and the ride height so we can dial out unwanted understeer and oversteer so we achieve a more neutrally handling car at the limit of grip.

SUSPENSION SHOPPING LIST


Whilst there are alternative products on the market our personal view on track car suspension would include the following where applications exist.
  • Uprated Bushes
  • Uprated Engine and Gearbox Mounts
  • Stiffer Antiroll Bars
  • Metal Bearing Top Mounts
  • Strut and Chassis Braces
  • Adjustable Suspension Arms
  • Adjustable Coilover Kit
  • Professional Suspension Geometry Alignment Set Up
  • Continual Checking and Testing of Set Up
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PROFFESIONAL SUSPENSION ALIGNMENT SET UP


Whilst getting a professional suspension geometry alignment set up is at the bottom of our list because you have the suspension geometry alignment set up done when you have installed all the other components on the list, it is important to understand what it is so you can understand what the other parts on the list will do for you in respect of this.

When you take you car to an experienced alignment specialist (one that understands the needs of race cars (not just putting the alignment back to original settings) they will usually have a conversation with you about what you are doing with the car (road and track day, mostly track day, full race car etc) and what your preferences are (safe understeer or a fast loose rear).

Based upon your needs and their experience they will be setting all four corner weights (to even out the weight of the car on the track at the tyres), front toe, camber and caster and the rear toe and camber where adjustability is possible. They will be looking to set the wheels of the car in such a position that the tyres will maintain their maximum contact patch with the track during hard cornering for maximum grip with either the understeer or oversteer characteristics you want at the limit.

This service cannot be underestimated as a very good initial set up for your car after bolting on your suspension modifications. With adjustable parts (arms top mounts antiroll cars, coilover ect) you can tweak the set up to further maximise cornering speed or change handling characteristics.

Be aware though that OE parts such as suspension bushes and top mounts (even if they are brand new) will allow a degree of flex in suspension components thus allowing the suspension alignment to change a little under hard cornering (and acceleration and braking for that matter). OE suspension parts (dampers, springs, antiroll bars etc) rarely give you the adjustability you need to get the correct suspension geometry alignment. Hence it is worth planning to upgrade as many of the suspension components on the shopping list as possible for the greatest increases. Read on to find out why!

UNDERSTANDING GRIP


Your tyre’s grip on the road allows you to accelerate, brake and turn. There is a limit to the amount of grip your car will have depending upon a number of factors such as the drive layout (RWD, FWD, 4WD), the weight distribution within the car, suspension setup and weight transfer. We will assume you won’t be changing the drive layout or significantly altering the weight distribution within the car. We could of course increase grip by fitting sticky track day tyres and be done with it (although the high side loads generated by these tyres will quickly ruin your OE dampers or road biased coilover kit very quickly) but it is far better to understand grip, what and how components can affect it so we can change them, have a professional alignment done then fit some sticky tyres so we have the most gain in grip possible.

Weight transfers occur as a result of the chassis twisting around the car's roll centre. In simple terms, whilst accelerating, braking or steering, your car’s body “rolls” in the opposite direction. If we move weight away from a pair of tyres, grip will reduce, if we move weight towards a pair of tyre, grip will increase.

It stands to reason then, when you accelerate, the weight of the car is transferred towards the rear of the car, the rear suspension compresses and grip at the rear increases whilst decreasing at the front. In a rear wheel drive car this increase in grip at the rear can help increase traction and reduce wheelspin, whilst in a front wheel drive car, as the front wheels loose grip due to the rearward weight transfer, traction loss and wheelspin becomes more likely. The opposite happens when you brake, the weight of the car is transferred towards the front of the car the front suspension compresses and available grip at the front increases whilst decreasing at the rear which can cause instability under braking causing the car to spin.

When you turn a corner, the weight of the car is transferred laterally. If you are turning right, weight is transferred towards the left side of the car, the left side suspension compresses and available grip on the left side of the car increases whilst decreasing on the right hand side (and vice versa). It is worth noting that weight transferred whilst cornering can increase grip and get you through the corner quicker ONLY if the steering is used progressively and weight is transferred smoothly. However, if you turn into the corner too quickly, the sudden transference of weight can unsettle the car and cause the tyres to break traction suddenly often resulting in a spin.

So now we understand what is happening to our tyre’s grip on the road when we accelerate, brake or turn we, can look at increasing grip where it is needed. We will assume you have reached the limits of your available grip whilst cornering and that one of two things is happening. Your car is either understeering or oversteering. So how do we deal with it?

Understeer

In the understeer condition, your car will be trying to plough on straight ahead rather than driving around a corner. Accelerating makes the condition worse, taking your foot off the accelerator and even light braking sees grip return to the front wheels as weight is transferred to them but this takes time. Ideally we want to reduce understeer so we can get back onto the throttle early in the corner for maximum corner exit speed.

Reducing Understeer

To reduce understeer we need to induce greater weight transfer to the front wheels to increase their grip. If we stiffen one end of the car, we allow weight transfer away from that end. We can also alter toe and camber settings to increase front tyre grip.
  • Soften the front damping or stiffen the rear damping to encourage weight transfer to the front wheels.
  • Fit softer front springs or harder rear springs.
  • Fit a softer front anti-roll bar or (more likely) a stiffer rear anti-roll bar.
  • Increasing toe-in at the front and/or setting toe-out at the back encourages the rear of the car to break traction more readily than the front which has the effect of increasing grip at the front.
  • Increasing front camber can increase the front tyres contact patch on the road increasing its grip during cornering.
  • Reducing rear camber reduces the rear tyre contact patch at the rear will again encourage the rear to break traction more readily than the front increasing front end grip.
Oversteer

In the oversteer condition, your car’s rear end will be trying to get round the corner before the front! Accelerating makes the condition worse, steering into the slide and taking your foot off the accelerator can sort things out unless momentum has taken over at which point a trip backwards into the trackside scenery, tyre wall or crash barrier is very likely. Ideally we want to reduce oversteer so we can get back onto the throttle early in the corner for maximum corner exit speed without spinning into the scenery.

Reducing Oversteer

To reduce oversteer we need to induce less weight transfer to the front wheels to maintain grip at the rear. If we soften one end of the car, we resist weight transfer away from that end. We can also alter toe and camber settings to increase rear tyre grip.
  • Soften the rear damping or stiffen the front damping to reduce weight transfer to the front wheels.
  • Fit softer rear springs or stiffer front springs.
  • Fit a stiffer front anti-roll bar or a softer rear anti-roll bar.
  • Reducing toe-in at the front and/or increasing toe-out at the back encourages the rear of the car to break traction less readily than the front which has the effect of increasing grip at the rear.
  • Reducing front camber can reduce the front tyres contact patch on the road reducing front end grip with the effect of increasing rear end grip.
  • Increasing rear camber increases the rear tyres contact patch on the road increasing its grip.

UPRATED BUSHES


Suspension bushes are some of the most highly stressed components fitted to a motor car. They undergo enormous strains and in the most arduous of conditions with no maintenance or lubrication.

The material they are manufactured from is a rubber compound containing natural products which deteriorate with age. It becomes softer and more pliable, resisting the forces placed on it less and less. Therefore allowing more and more movement of suspension components and offering less and less control over the suspension geometry. This in turn causes accelerated tyre wear, braking instability and poor handling. This is the single biggest reason you can instantly tell the difference driving a three year old car compared to a showroom new one.

So we fit uprated polyurethane bushes to maintain our suspension geometry alignment because their superior design offers much more effective control of the suspension components to a much greater extent than normal rubber items. Polyurethane bushes are generally 25-30% (more in “race” versions) stiffer than new rubber items but with exactly the same noise absorbing properties.

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UPRATED and ENGINE GEARBOX MOUNTS


OE engine and gearbox mountings have a notorious reputation for premature failure, particularly when used in performance applications and under extreme driving conditions such as track days and motorsport. Fitting uprated engine and gearbox mountings give us a the piece of mind that these components will not fail but there are other benefits too.

The engine and transmission is typically a 200+kg mass swinging around under the bonnet of your car like a pendulum on its original equipment mounts. There are two primary ways this affects the handling. Firstly, the physical movement of the mounts under extreme accelerating, braking and cornering. This actually shifts the centre of gravity of the car in the worst possible direction. This can severely affect the car balance at the most critical time. When you control this physical movement of the drivetrain, it can significantly improve the precision feel to the handling, especially on a car running competition tyres and suspension. Secondly, they reduce “engine shake”. This is the movement of the engine caused by bump inputs from the main suspension system causing the engine to wobble on its mounts. The very large engine mass shaking around will cause unwanted dynamic forces on the car.

Lastly, lowering overall engine movement significantly reduces the stress on engine connections such as inter-cooler pipes, fuel lines, exhaust systems etc. Clearance between the engine and other critical parts such as a strut brace and other under bonnet hardware is maintained.

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STIFFER ANTI ROLL BARS


As with all OE suspension components anti roll bars are a compromise. They are fitted to give a degree of body roll control during cornering without having to stiffen the main road springs which would affect the comfortable OE ride quality. During hard cornering uprated anti roll bars resist body roll to a greater extent than OE items to push all four tyres into the track for extra grip. Many anti roll bars are adjustable giving you control over how much they act upon body roll. Fitting an uprated rear anti roll bar to the rear of a front wheel drive car can reduce understeer, an absolute must for track focused cars

Using uprated anti roll bars along side uprated springs and dampers allows you to specify main springs that will still have enough compliance to maintain traction over bumpy tracks and over the kerbs.

TOP MOUNTS


Whilst many coilover manufacturers supply their kits with camber adjustable font top mounts, some very respected brands do not on the basis that many race formula still don’t allow adjustable camber on grounds of cost (go figure!), you can still fit fixed and adjustable top mounts to these kits.

Uprated top mounts have a metal bearing instead of a rubber bush thus maintaining suspension geometry alignment during hard cornering. This improves grip and traction for faster more predictable corning and quicker lap times.

Camber adjustable top mounts allow you to increase or decrease front tyre grip to reduce understeer or oversteer for a more neutrally, faster handling car.

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STRUT BRACES


Believe it or not, car bodyshells are flimsy things, especially in older cars. We have even seen bolt in roll cages being hit by the bodyshell during hard cornering on certain older small hot hatches! Stiffening suspension mounting points with a strut brace and the body shell (with chassis and floor braces) helps to reduce this body flex during hard cornering to maintain suspension geometry alignment for faster cornering. They may also offer a greater degree of safety in the event of an off!

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ADJUSTABLE SUSPENSION ARMS


Most manufacturers do not build cars with much adjustability in the suspension arms and geometry alignment is set to understeer which is considered the “safe” default in road cars. In track cars understeer will slow you down and increase lap times as you are off the throttle for longer waiting for grip to return.

Fitting adjustable suspension arms will give us control over camber, caster and toe settings so we are able to set the cars geometry alignment so the tyre is flat to the track during hard cornering to reduce understeer and oversteer for a more neutrally handling car at the limit of grip for faster lap times.

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COILOVERS


For many modifiers fitting a set of coilovers is the be all and end all of suspension modification but there are many factors to consider of you want a useful increase in grip and traction rather than just stiffer suspension which may feel faster but often is not!

For track focused cars, fitting a set of height and damping adjustable coilovers will help to increase the total tyre grip by lowering the ride height for lower weight centre and increasing body roll control and weight transfer. They also have the advantage of allowing us to alter ride height and damper stiffness at the front relative to the rear. All of these factors allow us to alter settings so we can reduce understeer or oversteer for a more neutrally handling car at the limit of grip for faster lap times.

Many coilover manufacturers supply their kits with camber adjustable font top mounts (where space in the turret makes them a worthwhile addition). These are useful again to dial our understeer or oversteer although be sure that your chosen race formula allows these.

Some Words of Wisdom on Coilovers

It is worth noting that most retailers will want to shift boxes of coilovers with the minimum of fuss and thought. They would rather you buy online and don’t ask too many questions. Here at Corby Motorsport we work a little differently! We are able to offer full customisation of certain brands of coilover kit based upon the use and specification of your car. This is particularly useful as it means you pretty much get the ideal spring rates and damper valving for your cars use and spec straight out of the box.

It is also worth noting that all coilover kits are not made the same. We don’t get involved with cheap kits as these seem to be aimed at the modifier who simply wants a low ride height with little concern to performance and handling. These kits will have a soft damper to give some semblance of ride quality with a hard spring to combat the springs going coil bound. This mismatch give unpredictable handling. If you are looking for performance coilover kits, expect to pay a minimum of £500 - £600 depending upon the car. Look for brands that have a proven involvement in motorsport such as sponsorship of MSA sanction events. The MSA does not sanction cheap shit coilovers, if you are a track day enthusiast or racing in circuit events, you should not consider them either. We could sell shed loads of cheap kits and retire early. But we don’t!

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TESTING AND FINE TUNING OF SET UP


A great many modifiers simply through a set of coilovers on a car and immediately feel it faster. Chances are that is it actually a little quicker through corners due to the stiffer springs and dampers controlling weight distribution but it could probably be so much faster!

If you have fitted the components required to increase your cars suspension adjustability, had a company (such as ours) specify your coilover kit correctly and had a professional alignment performed, you are almost there. Certainly ready to hit the track with the best possible initial set up! Testing and fine tuning your set up now becomes important but incredibly so few track dayers actually bother!

What we have tried to achieve with our uprated parts and suspension geometry alignment is a car that corners neutrally without exhibiting excess understeer or oversteer, if we have achieved this then the tyre contact patch on the track will be flat during hard cornering for maximum grip. This means the tyre temperatures measured on the outside, middle and inside of the tyre should be about equal.

Tyre Pyrometer

Purchasing an inexpensive tyre pyrometer will allow you to measure tyre temperatures and make adjustments to geometry alignment to even out any mismatched tyre temperatures to increase the overall tyre contact patch with the track. There is a lot of information on the internet about using tyres temperatures to determine set up changes and it is a procedure that will help you get the most from your set up.

Set Up Sheets

Most track day organisers do not allow timing but if you can find a way then recording camber, caster and toe settings along with tyre pressures and temperatures and the weather against lap times is a good way of proving which settings you change over the course of the day worked for your driving style, confidence and lap times. There are plenty of examples of set up sheets and you can use them as simply or as complicated as you want or need to!

So if you made it this far you should now be ready to plan your suspension modifications. Click through to visit our SUSPENSION SHOP for the best brands and the best deals!