Suspension setup explained

[92GTSTproject]

Basic Concept

Ride

Basically, suspensions are employed to deal with humps in the road surface, in other words, enhancing ride comfort. When a car rides over a hump, the springs are compressed, store the energy thus provide shock absorption. The energy will be released quickly when the springs bounce back. Dampers are employed to smooth and slow down the bounce motion, this is called "Damping". Without dampers, the car will bounce up and down severely and quickly, this is perceived as uncomfortable. Study found that ride is perceived as comfortable by human when the bouncing frequency is 1 to 1.5 Hz. If it exceeds 2 Hz, most people feel the ride harsh. Therefore ride quality is mostly controlled by the selection of suitable springs and dampers.

Handling

In order to achieve ride comfort, we create suspensions that let the wheels move with respect to the car body. Inevitably, this creates many many problems in handling. When the car is turning quickly into a bend, centrifugal force will roll the car body. Body roll leads to the weight transfer towards the outside wheels, it also changes the suspensions geometry which changes the camber angles of wheels. Change of camber accompanies with weight transfer result in unwanted understeer or oversteer. If brakes are applied in the bend, castor angles will also be changed, that may further deteriorated understeer/ oversteer or even introduces torque steer. (Don't understand ? No problem, you will have a clearer view in the following paragraphs)

Camber
This is a very important concept we must learn before going on
As shown in below, if a wheel is not perpendicular to the road, then it is cambered. If it leans towards the center of the car, then it is negative cambered. If it leans outwards to the car, it is positive cambered (as shown in the following picture.)


When a wheel has positive camber, due to the elasticity of tires, the wheel will be reshaped to something like the base of a cone. It will have a tendency to rotate about the peak of the cone, as shown in the picture. Now, you will see the wheel tries to steer away from the center of the car.

If both the right and left wheels are positive cambered (that means they lean towards opposite directions), the steering tendency will be cancelled so that the car remains running in straight line. If the car is turning into a corner, body roll puts more weight on the outside wheels than the inside wheels, that means the outside wheel's steering tendency will have more influence to the car. As the positive-cambered outside wheel tries to steer the car to the outside of the corner, the car will understeer.

On the contrary, if both wheels are negative cambered, the car will oversteer.

A Good Suspension must :

1) Provide independent shock absorption to individual wheels. That means, when one wheel rides over a hump, the shock will not be transferred to other wheels.

2) Has adequate body roll. Excessive body roll leads to too much weight transfer thus influence the steering response. It is not comfortable too. Restrict body roll to minimal may create uncomfortable feeling because of excessive g-force. Moreover, body roll could provide information to the driver, telling him the state of cornering and whether the car has reached its limit. Completely eliminate body roll is not at all good.

3) Has a good geometry such that wheel cambers remain unchanged in all conditions, that is, acceleration, braking, cornering, load and bumps.

Body roll suppression usually conflict with ride comfort, because the former requires stiffer spring and dampers while the latter vice versa. Nevertheless, clever suspension geometry may improve body roll without altering the ride. Here in below we are going to discuss the most popular kinds of suspension geometry.

Non-independent suspension

Live / Dead axle



Until the late 70s, most cars still used this simple non-independent suspensions, especially at the rear axle. Basically, it is a rigid axle fixed between left and right wheels. The car body is suspended by leaf springs or coil springs on the axle / wheels unit.
As you can see, the wheels are not independent. When one wheel rides on a hump, the shock will be transferred to another wheel. Besides, both wheels will be cambered, thus non-neutral steering is inevitable.

If the axle is also the driving axle, it is called Live Axle. Live axle is very heavy. It consists of the final drive / differential, drive shafts and a strong tube enclosing all these things. Since the whole axle is rigidly fixed to the wheels instead of suspended by springs, the so-called Unsprung Weight is very high.

What is the result of high unsprung weight ? Assuming a live axle meets a hump and "jump" quickly upward, the more weight it has, the more momentum it gains (because momentum = the product of mass and velocity). That means the more momentum the springs have to deal with. Of course, springs cannot absorb all the momentum, so eventually part of the latter will be transferred to the car body in the form of shock. Therefore live axle is never good at ride quality.

If the axle is not the driving axle, it is called Dead Axle. Without the driving mechanism incorporated, dead axle has much less unsprung weight, so its ride quality is better than Live Axle. Anyway, comparing them is useless - it does not make sense for a car to use dead axle in the non-drive wheels while using a suspension advancer than live axle in the driving wheels. Independent MacPherson suspension is rather easy and cost-effectively to replace the non-drive dead axle. If a car maker cannot afford such little additional cost, it must not willing to employ advancer suspensions in the driving wheels also.

Live / Dead Axle have another disadvantage - body roll is not sufficiently suppressed. Springs are the only element which control the body roll, however, stiffen the springs will inevitably deteriorate ride quality. Moreover, if coil springs are used, lateral force due to cornering will lead to transverse movement of the car body, thus result in weight transfer and affect steering response.

The popular solution was to add some control arms between the car body and the axle, such as Panhard rod and Watt link. However, they are out of our scope.

Advantage: Cheap. Body roll does not influence the camber of wheels.
Disadvantage: Non-independent, bad ride quality, both wheels cambered on bump.
Who use it ? Some American sedans, Ford Mustang, Falcon, most SUV.


DeDion Axle



Although independent suspensions were invented decades ago, non-independent suspensions still dominated the market until the late 70s. The first reason was: cheap. The second reason: it offers quite good handling despite of poor ride. Since the wheels are rigidly linked by an axle, they remain perpendicular to the road surface regardless of body roll. Therefore the car corners quite stable. In contrast, in many types of independent suspensions, camber angle may be changed due to body roll.
However, as explained before, live axle has too much unsprung weight, thus leads to poor ride quality. Therefore many budget sports cars or coupes chose DeDion Axle (rear) suspensions over live axle.

DeDion axle suspension has much less unsprung weight because the final drive / differential and driving shafts are not rigidly attached to the wheels. Like independent suspensions, they are part of the car body and flexibly linked to the wheels by universal joints. In other words, they are sprung.

The wheels are interconnected by a DeDion Tube, which has a sliding joint to permit wheel track variation during suspension movement, this help refining ride quality too. The DeDion tube keeps both wheels parellel to each other under all conditions, so they are always perpendicular to the road surface regardless of body roll.

Advantage: Still cheaper than most independent suspensions. Body roll does not influence the camber of wheels. Better ride quality than Live Axle.
Disadvantage: Non-independent, ride is still worse than independent suspensions. Both wheels cambered on bump.
Who use it ? Caterham, Vector, Smart.

[92GTSTproject]

TUNING YOUR SUSPENSION SETUP

A proper lowered suspension uses aftermarket adjustable arms and links to lower the vehicles center of gravity and still be able to keep with in proper alignment specs set by the manufacture or for best handling a custom setup can be used knowing how each change affects handling

Ride height is usually measured in inches, from the rocker panel to the ground. A good wheel alignment chart should provide specs, but the main thing is that the measurements should be within 1/4 inch from side to side and front to rear.


Caster:
Viewed from the side, the caster is the tilt of the steering axis. When the wheel is in front of the load the caster is positive. Three to five degrees of positive caster is the typical range of settings, with lower angles are being used on heavier vehicles to reduce steering effort.



If the caster is out of adjustment, it can cause problems in straight-line tracking. If the caster is different from side to side, the vehicle will pull to the side with the less positive caster. If the caster is equal but too negative, the steering will be light and the vehicle will wander and be difficult to keep in a straight line. If the caster is equal but too positive, the steering will be heavy and the steering wheel may kick when you hit a bump.

Caster has little or no effect on tire wear.

One of the best ways to visualize caster is to picture the caster on a shopping cart. The pivot while not at an angle intersects the ground ahead of the wheel contact patch. When the wheel is behind the pivot at the point where it contacts the ground, it is in positive caster.

Like camber, on many front-wheel-drive vehicles, caster is not adjustable. If the caster is out of adjustment on these vehicles, it indicates that something is possibly bent from an accident, and must be repaired or replaced.

Negative Camber:
increases the cornering grip of the tire during cornering, helping to maximize grip and providing better traction. Too much Negative Camber will increase the inside tires wear and could result in handling imbalances.

Neutral Camber:
best suited for maximum acceleration and braking, this set up makes sure a flat contact patch is retained on flat road surfaces. The inside wheels may lift on the inner contact edge of the tire duration extreme cornering.

Positive Camber:
used more for off road applications, especially with agricultural vehicles as this setting helps the wheels to turn with lighter steering effort required.The outside wheel under extreme cornering loads will benefit, but camber levels are normally linked ( might be a consideration for oval tracks).

Anti-Roll /Sway Bars:
can provide adjustable settings in the suspension set up. Especially useful in dialing out oversteer, or understeer handling characteristics and getting a better balanced car. They are the same effect as changing the springs, but their effects are only used in lateral cornering forces.

The reason this is so useful, is that you can make adjustment to front and rear independently with out affecting other suspension settings. Stiffer settings will reduce body roll, while softer settings will increase body roll. The relationship between the front and rear settings ( roll coupling), will also have a direct affect on the handling of the car. Like most suspension adjustments, it is best to take small incremental adjustments rather then going to one extreme to the other.

It is critical that the right Anti-Roll/Sway Bar is also selected to complement the other suspension components. I would suggest seeking profession advice on the overall suspension set as a whole and not just individual upgrades, when considering suspension adjustments.

It is generally accepted that it is better to reduce the settings, rather then increase them to get a better balanced car. Softer settings will make weight transfer more gradual, with less abrupt loading, bending into corners rather then darting into them. Great care needs to be taken with too soft a setting as well, if the car has a low center of gravity, a soft setting could result in the car bottoming out. Also camber settings ranges could be affected with a soft setting, where the tire exceeds the optimum set up.

Having too stiff a setting could result in poor handling in tight corners, with the inside wheel lifting off the ground. Also if either of the two wheels linked on the axle are on different road surfaces (one wheel on track, other on the side of the track), having a stiff set up will result in imbalances being transmitted through the Anti-Roll/ Sway Bar to the other driven wheel.

Understeer: reduce front or increase rear anti-roll/ sway bar settings.
Oversteer: increase front or reduce rear anti-roll/ sway bar settings.

Damping Effect On Cornering:

Bump:
Front Bump Increase= Understeer.
Front Bump Decrease= Oversteer.
Rear Bump Increase= Oversteer.
Rear Bump Decrease= Understeer.

Rebound:
Front Rebound Increase= Understeer.
Front Rebound Decrease= Oversteer.
Rear Rebound Increase= Oversteer.
Rear Rebound Decrease= Understeer.

The center of gravity:
can be seen as the balancing point of the car, if you hung a car from a cable above the ground it would be balanced perfectly. It can be hung from any dimension and would remain balanced, it can be viewed as the center point of where the majority of the mass of the car is located and is a 3-D location across different axis's.
It is critical to understand that all acceleration, braking and lateral g-forces go through this point and the whole suspension system is set up and designed around this point. Although in reality we have little adjustments of the center of gravity (unless we design a race car ourselves), understanding it's importance and effects is import on fine tuning suspension set ups.

Generally speaking we want to have a car with a center of gravity as low to the ground as possible, this helps reduce weight transfer loads acting on the roll center. Less weight transfer downloads through high suspension loads, will result in better tire performance. This is because as the load increases on tires, their ability of efficiently converting the vertical download decreases (coefficient of friction). The longer the wheelbase and wider the track of the car, in relation to the center of gravity, the less the weight transfer loads.

This also affects the cars dynamic roll centers, as the center of gravity acts as a lever on this point. The roll center is a point at which the suspension is designed to rotate around, this point changes fore and aft with acceleration and braking forces, also horizontally with left and right lateral forces in the opposite direction. The further the roll center is away from the center of gravity, the more roll or weight transfer happens, getting a balanced suspension set up which handles predictable past the limit is the ideal set up.

Weight Distribution:
the final section we need to look at, we might of adjusted all the other settings listed above but the car still might be displaying understeer or oversteer characteristics during left or right cornering loads ( normally one or the other). The ultimate aim of suspension tuning is to try and get a perfectly set up car, which is balanced during cornering in both directions and maximizes equal loads through the tires. Also cars with rear wheel drive layouts will have increased acceleration with more weight over the rear wheels to aid traction

Static Weight-
If we take a static car which is fully loaded with all fuels, oils and driver on board, ideally we want equal corner weights distributed equally across the car (50% left, 50% right at the front and rear of the car). While the overall car designs drivetrain layout will play a fundamental importance in the total fore and aft static weights, it is possible to still make some changes to increase this ideal balance harmony (normally through moving components like batteries, fuel cells ect).

It is always best to to get your static weight measurements in the first instants before making any radical suspension changes. This can be calculated with digital scales designed for the job, and will best be done when new suspension components are fitted to the car.

Front Wheel Drive= more weight over the front of the vehicle, normally 60:40 split.
Front Engine, Rear Wheel Drive= tend to be very balanced with 50:50 split possible.
Mid Rear Wheel Drive= more weight normally over the rear of the vehicle, 40:60 split.

As soon as the car is in motion, the car's weight will act through the center of gravity and affect the suspension's roll center during acceleration, braking and cornering loads. This is also when any uneven static load rates will transmit themselves into understeer or oversteer, when cornering.

Bear in mind the following rules:
If we increase the FL and FR spring perch (adjustment ring), then only ride height increases.
If we increase RL and RR spring perches, then only the ride height increases.
If we either increase the FL and RL or FR and RR ( one side of the car), we only increase the ride height.

Corner Weights-
Before we adjust the corner weights to get a perfectly balanced car, or as close as is possible under the design constraints, we need to check that we have the following checklist:
tires inflated to the desired pressures.
anti-roll bars are disconnected.

You MUST HAVE a method of recording the small adjustments , this is very important as it may take multipule changes to get the desired corner weights.

[92GTSTproject]

if anyone has anything to add please do

[Skym]

With swaybars, they are matched to shocks, springs. It's missing what happens when there's too much swaybar and too little swaybar vs springs, shocks.

Also swaybars help to stop suspension expanding and pushing car over causing more bodyroll when car corners. I learnt this via having failed bushes (more bodyroll) vs non failed bushes (less bodyroll). Most of the time failed swaybar bushes (crushed or cracked) are the cause of excessive bodyroll that sometimes gets blamed on suspension.

Also doesn't mention that monoque chassis can be out of square by as much as 13mm, so needs to be adjusted for with alignment, suspension.

[S13Jordie]

a lot of good technical stuff on www.motoiq.com

[92GTSTproject]

Mike Kojima is a brilliant engineer, however, you already need to know the above stated information to understand what he talks about as he doesnt actually tell you how to fix understeer/ oversteer or how to set up your car, it says the ultimate guide to suspension, but doesnt explain anything, his write ups are mostly him just filling time when he's bored, my write up actually tells you how to get the baisic setup on your car not a pro drift car if you want a suspension set up like that go see Mike, cuz **** that he talks about is race car engineering and you have to pay for set ups like those, this simply tells you how to make your car handle well

[Skym]

There's many ways to dial out understeer, ride height, swaybars, alignment plays a small part, etc.

That's because each car is different with setup (springs, shocks, swaybars, etc), depending on what you are doing with car (street, racetrack, drift, drag) and the mods on car. What suits one car won't suit another unless the cars are identical (factory car).