Suspension Bushings - More Than Just Rubber

Suspension Bushings - More Than Just Rubber

If we look at the car as a whole, it can be likened to the human body, with each component having a similar equivalent to a body part. As we’ve discussed in previous articles, the chassis acts as the skeleton of the car; by following this example, parts such such as control arms and suspension linkage act as the car’s limbs. Much like human limbs, the joints on control arms and suspension require something to prevent friction. For humans, we have cartilage at our joints, whereas vehicles use bushings.


Suspension bushings are small, round parts placed at the joints of your car’s suspension components. Bushings come in a wide variety of types in materials to suit different use cases. As insignificant as they may seem, these small little devices find importance in your car’s suspension due to the sheer amount of them used. The ND Mazda Miata, which uses double wishbones in the front and multi-link suspension in the rear has over 30 bushings. By swapping out all of these bushings, one can imagine the change it will bring. 


In the case of passenger cars such as the Honda Civic and Toyota Corolla, the factory bushings are designed to provide low cost, durability and comfort. These bushings usually consist of an inner and outer sleeve with a large rubber inner insert; the insert helps absorb vibration and noise that would otherwise be transmitted to the cabin. Under most driving conditions, rubber bushings are the best choice; unfortunately, the rubber rigidity which is ideal for most production cars falls short when placed into a performance driving scenario.


Bushing Deflection - What Is It?


Bushing deflection is what occurs when the material in a bushing (rubber in this case) is deformed due to external forces. If you’ve ever rubbed an eraser too hard and noticed it bending one way and another, you’ve experienced what bushings go through when overloaded. Suspension geometry and alignment is only effective if the components do not move or change position. Bushing deflection occurs when cornering loads force the inner sleeve to move out of the center as the rubber compresses on one side. Due to the vast number of bushings in varying places, the effects it can have on handling are significant.


Bushing Deflection And Camber 


A tire can only exert its full cornering force if the contact patch is making full contact with the road surface. When vehicles with independent suspension are faced with bushing deflection,. the front control arms will move in relation to the frame. When the control arm is forced to move, the wheel is forced to move with it, causing the camber value to become positive. When the rear camber value changes on a rear-wheel drive car with an inexperienced driver at the wheel, the loss in traction can cause oversteer. 


Bushing Deflection’s Effects On Steering And Toe



The steering linkage on your car uses rigid links and joints, resulting in very little deflection when exposed to high cornering forces. Due to the bushings used for the control arms, deflection can cause the arms to move while the linkage stays in place. When the deflection occurs, the steering angle changes even if the driver holds the steering wheel steady, resulting in “twitchy” steering. 


The effect caused in the steering of the car via deflection varies on the placement of the steering linkage in relation to the steering knuckle. Deflection Understeer occurs when the linkage sits in front of the knuckle and causes the tire to turn less than what the driver asks. Deflection Oversteer occurs when the linkage sits behind the knuckle and causes the wheel to turn more than what the driver asks. Deflection oversteer is generally considered to be safer and thus the linkage position is behind the knuckle in most modern cars. 


A wheel’s toe angle can have a direct effect on a car’s handling, for better or worse based on the situation. In the past, Porsche’s use of a Weissach Axle on the 928 reduced oversteer by having the toe adjust itself mid-corner. The Weissach Axle was essentially a modified version of a semi-trailing arm suspension setup; the front pivot bushing from the trailing arm was replaced by a short link, which causes the rear wheel to toe in as the load on the wheel increases, acting as if the car had four wheel steering. 


On the 2nd generation (FC) Mazda RX-7, a special bushing that was designed to deflect after forces of 0.4G or higher acted on it was used. The end goal of this was to have a similar effect as the Weissach Axle while using a traditional semi-trailing arm layout. This special bushing only allowed the deflection to let the car toe inward. In other cars with trailing arm and semi-trailing arm rear suspension, bushing deflection will cause the toe to move inward when power is applied, while braking the toe moves outward. With an inexperienced driver at the wheel, the toe’s instability is detrimental to driver confidence and the overall driving experience. 


Replacing Your Factory Bushings - Choosing The Right One For You


Even though bushings are a wear item, their replacement is largely ignored by many drivers. The rubber used in the bushing can wear from driving wear and tear as well as weather changes and old age. If you’re looking to change out your bushings either due to wear or to reduce/eliminate deflection, it’s important to choose the right type 


Installing factory rubber bushings will provide those looking to restore comfort, noise and handling to factory levels with the solution they need if they are not looking for performance. This is the best choice for most drivers. 


On the other hand, aftermarket rubber bushings usually use rubber with a higher durometer (hardness) than your factory bushings. These bushings are less prone to deflections but still keep many of the advantages associated with rubber bushings including low cost, vibration/motion absorption and low noise. 


Urethane bushings are a popular solution for drivers looking to eliminate deflection due to their cost and stiffness, however these aren’t perfect. It is a common misconception that urethane bushings work in a manner akin to that of a hard rubber bushing, however that is not the case. Due to the nature of suspension joints moving, a bushing must be able to allow movement, usually in the form of rotation. With rubber bushings, the soft nature of the material allows a bushing to twist under load. Due to this deformation occurring in the rubber itself, there is no need for the bushing to be lubricated. 


Urethane Bushings are so stiff that they technically work as bearings, so a sliding motion must be allowed on the inner surface. As a result, Urethane bushings require frequent greasing to provide smooth operation. One the grease wears out, the urethane begins to bind to the metal surface, causing squeaks and knocks as the suspension moves. Eventually the urethane will stick to the suspension joints, causing them not to operate correctly. Some bushings have an inner sleeve which have grease retention channels to cut down on maintenance intervals, however periodic lubrication is still required. 


Steel Bushings operate similarly to urethane bushings - they are essentially bearings, and require periodic greasing in order to work properly. Steel bushings do not have any deflections, however NVH is sharply increased. These bushings are used in some race cars where noise and vibration is not a concern. 


Nylon Bushings are more expensive than Urethane bushings and they require periodic lubrication, however these far outlast rubber bushings, with many lasting upwards of 100,000 miles. When the outer sleeve is fitted with a zerk fitting, you can easily lubricate the bushings without having to constantly disassemble control arms.


Provided that your new bushings allow for rotation without binding, you will not see much of a difference in ride quality. To keep the parts moving freely, many of the solutions described above must be greased when necessary to allow for the necessary motion. The main noticeable difference is the increase in road noise being transmitted to the cabin. To many, benefits from the increased performance of harder bushings far outweigh the negatives, but ultimately the choice is yours. Solid Bushings are available from Legsport while hardened rubber bushings are available from Autoexe on our online store. 


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You've Lowered Your Car. Here's What To Do Now

You've Lowered Your Car. Here's What To Do Now

Lowering your car is a very popular vehicle modification across the globe, and when done correctly, can increase the performance of your car. Like most modifications, it is prone to adverse effects if done incorrectly; luckily, the issue can be remedied with readily available modifications. We'll be covering two points of correction - sway bar end links and tie rods.

Adjustable End Links

Sway Bar Linkage - The Unsung Hero! This is one of the most overlooked suspension upgrade items.


For cars equipped with anti-roll bars, replacing the factory end link is required to get the correct functionality back once lowered. When the vehicle height is changed from factory specification, the end link's position will change, causing the sway bar's angle to change along with it. By having the angle changed, the spring effect which allows the anti-roll bar to work has its effectiveness reduced. An anti-roll bar is considered as another "spring" to your suspension; if not correctly positioned, the bar can add to suspension pre-load, which distorts the normal suspension spring effectiveness and spring rating.  In most cases, you really want to have you sway-bar to have no or little tension when driving normally, which can be achieved by correcting the angle.  Adjustable sway bar end links allow you to lengthen or shorten the link's length in accordance to your vehicle's ride height so the sway bar angle can be corrected. For ease of adjustment, it is recommended to install your suspension (coilovers/lowering springs) and adjustable end links at the same time.

Adjustable end links are available from AutoExe and Legsport for select vehicles. The LegSport challenge damper coilover kit for the FR-S/BR-Z includes a set of adjustable end links for the front axle only. 

Tie Rods


The factory tie rod is a critical part of your vehicle's steering system as it allows your wheels to change direction by taking the input in from the steering rack. The factory tie rod is designed to work with your stock suspension; any modification that changes ride height, such as the installation of lowering springs or coilovers will cause the tie rod to sit at angle. The new angle of the tie rod causes a change in toe, which ultimately results in bump steer during cornering. By using a tie rod which restores the ball joint length to the factory setting, you can keep the original handling characteristics. 

The Sports Tie Rod from Auotexe is available for Mazda owners who would like to correct the steering characteristics on their car. The AutoExe tie rod is made from high strength forged carbon steel (S45C). 

When doing any modifications to suspension geometry, it is important to get a wheel alignment as soon as possible to restore handling characteristics and to eliminate adverse tire wear and to really benefit those drivers looking for precise handling and steering input feel.
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Experience

Experience "TUNE COOL!" With AutoExe Suspension

Personalizing Handling For Your Car

If we take a quick glance at the diversity of people in regards to wants and needs, you'll see that "One size fits all" doesn't really fly. Due to this diversity, you'll see cars of different classes and price brackets, all tailored to fit a target audience. In this regard, the priority of vehicle suspension and the type of suspension used varies with the application. For example, sharp, responsive handling is a priority for sports cars, whereas for SUVs and sedans, and emphasis may be placed on cruising comfort. In the automotive bell curve, you'' find that mass produced vehicles are built on the premise that the suspension should not provide discomfort while driving. To achieve this goal, an equal balance of handling stability and riding comfort is emphasized. It is only natural that a driver who wants to experience a sportier drive would want to bring out capabilities in their vehicle that could not be achieved through the offerings of a mass-produced vehicle. The beauty of vehicle tuning, is that it allows those who seek more power, sharper handling, etc to fulfill their goals. 

Refining Transient Driving Characteristics, The AutoExe Way

AutoExe's suspension seeks to increase the relationship between car and driver, bringing them in sync and heightening interaction. This concept builds on the concept of Jinba-Ittai, the idea that a horse and the rider are unified as one. This harmony can be felt when cornering; the relationship starts when you begin to turn the steering wheel and the car begins to roll. When you are able to trace a line accurately, the relationship between man and machine is brought to new heights. This sensation of driving which could not be achieved at the mass-production level is what AutoExe seeks to bring to you. Here's how Autoexe's tuning method achieves this handling target, step by step.

Spring Ratio

Determining the correct spring setting is important, as this will determine the roll rigidity (amount of roll). Although it's true that the lower the vehicle's height is, the lower the center of gravity becomes, the distance between the center of gravity and roll center also changes, forcing the roll to become stronger. In addition, if the suspension stroke is shortened too much, the vehicle can bottom out frequently (Riding on bump stop bushing). In order to prevent the aforementioned shortcomings, it is necessary to increase the spring rate to match the height reduction, but in doing so, the ride comfort deteriorates. 

AutoExe judges driving, comfort and safety on the street from multiple perspectives, and uses a general reduction of around -20mm for sports cars and -25mm for SUVs with a high center of gravity. Once the appropriate amount of height reduction is determined, the minimum required spring rate is determined based on the sprung weight of the vehicle. Their tuning philosophy aims to acquire handling characteristics that match the driver's expectations without sacrificing ride comfort during urban driving. Depending on the vehicle, the spring constant is increased around 10-30% higher than the factory spring rate. When combined with the specially chosen damping force, a fine balance of ride quality and maneuverability is achieved. An exception to this rule is the AutoExe Ultimate Sports suspension kit, which gives the highest priority to handling and roll rigidity; ride comfort takes a back seat for this specific kit.

Accurately Setting Damper Force


The job of a suspension damper is to convert the vibration energy of the spring into thermal energy while reducing it. As seen on the diagram above, Autoexe's damping ratio* has the damping force emphasis placed at low speeds, where initial roll rigidity begins to be affected (Blue Box Area). Every single line of AutoExe dampers have been designed to offer the highest priority on extension at the very low speed range, where piston speeds range from 0 - 0.1 m/sec. The reason for doing this is simple; The damping force of the damper is rated as a value at 0.3m/sec, however the initial roll that occurs at the entrance of a corner or turning is done in a smooth manner as this happens below the rated value (specifically speaking, where the damper begins to move). 

By increasing the damping force in a sharp curve (initial vehicle roll) from a very low speed range (shock movement speed) where the piston speed is 0.05 m/sec or less, the roll speed from the moment the steering is turned is suppressed. By reducing the roll angle (deg/sec), the fear of sudden roll is decreased, as the car rolls gently for an heightened sense of security when cornering. The increase in damping force goes away after speeds of 0.1 m/sec to provide the accurate energy absorption over dumps and road imperfections. The total damping force value is allocated on the extension side while being kept low on the compression side for the same reason (Blue box area). All AutoExe dampers are designed to be as close to the ideal value** as possible (Red Boxed Area)

*This is the ratio between the damping force of the damper and the critical damping force (the last-minute damping force that determines whether or not the spring vibrates)
**The standard of development is a piston speed of 0.05/0.1/0.3 m/s and a damping ratio of 70/50/30% respectively 

The blue line marks the ideal curve which shows the absolute value of the damping force. The damping ratio curve is marked by the red line which is the same as the concept of damping ratio (index of how hard the springs move). The damper is more effective (higher damping ratio) when the piston speed is lower. 

In the world of aftermarket dampers, adjustability of damping force has become mainstream (A marketing feature?), yet AutoExe has stuck with fixed (non-adjustable) damping. As AutoExe's damper design places emphasis on the low-speed movement when the damper begins to rise, adopting a fixed piston results in a simpler path for the damper oil. By eliminating the extra oil paths from the adjustment system, the wasted pathways for oil are gone, allowing the damper oil's resistance to be converted into damping force more efficiently. This design increases the initial response of the car by delaying the speed of roll, squat, and nose dive without increasing the spring rate; this applies irrespective of whether the damper is mono-tube or twin-tube.

AutoExe's suspension suite is more than just spring and dampers - they include adjustable stabilizer links, sports tie rod ends, anti-roll bars and hardened bushings. The use case for each of these individual items will be covered in future articles. 

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Understanding

Understanding "Core Strength" With Chassis Bracing

There is more to chassis braces than earning points at car shows...  obtaining knowledge about them could very well make you a bit more versed about your performance upgrades. After all, knowledge is power!

The quest to increase chassis reinforcement is sought after by auto enthusiasts all over the globe. The most common modification done to achieve this goal, is to use a metal brace which connects the two front strut towers together. While this is a very common thing to do, many people will add a strut tower brace or any other body bracing without fully realizing what it does. 

In truth, chassis bracing is designed to give a sense of unity to the chassis, but this "unity" is fully realized only when you realize what the chassis brings to the performance aspect of your driving. The true key to chassis reinforcement is to allow your suspension to work more efficiently, ultimately allowing you to get the most out of your tire. Below, we'll be talking about how chassis reinforcement effects the suspension, steering and ultimately the tire. 


Core Strength

If we look at human structure, underneath the layers of muscle lies the skeleton. Having this core structure be strong is crucial during athletic activity, particularly during sports. Similarly for cars, having a rigid chassis provides the correct framework for high-performance driving. 

While driving, the input from the road surface is sent from the tire to the suspension, ultimately making its way to the chassis; this feedback is sent to the driver through the seat and the steering. On the flip side, the input from the driver's steering is transmitted to the road in the opposite direction in this "closed loop". In order to provide accurate inputs from both sides, all components inside this closed loop need to function accurately. 

Chassis Strength - Unity During Cornering

It is often said that the three key points for driver enjoyment and performance in vehicle control are the actions of acceleration, braking and cornering. To experience confidence and enjoyment when pushing the car, it is vital that the three aforementioned items perform with immediacy and with accuracy. 


Take a look at the above diagram, which displays a vehicle without adequate chassis bracing on the front shock towers. As mentioned in the previous article concerning the Motion Control Beam, a vehicle's chassis is designed from multiple spring elements which can cause body distortion and vibration. Due to inadequate torsional rigidity, the cornering forces have been transferred from the tire, into the suspension and into the chassis. As the chassis has begun to act as the weakest link, the input from the tire is absorbed by the chassis, and distortion occurs. Due to the "closed loop" nature of this system, your steering input going to the road will also be affected. 

The ultimate consequence of a disconnected chassis such as the one above is handed down to your tire. If the lateral rigidity of the body is insufficient during cornering, the gripping force from the tire will be absorbed by the chassis through the suspension, instead of being applied to the road. When coming from the opposite perspective of the driver, the action of turning the wheel does not see the full potential as the body distortion causes a delay in turn-in performance. 

The more traction that is available to a tire, the worse this phenomenon gets. Furthermore, having an inadequately rigid chassis will not allow you to take full advantage of your tire. If you are looking to maximize your tire performance, or feel that the tire's performance is "veiled",  it may be time to look into chassis reinforcement. 


The above diagram displays a vehicle with bracing on two points- the shock tower and across the front cross member. By reinforcing the front cross member, deformation of the pivot point under the suspension is suppressed. 

One notable example where you will experience the benefit of a connected chassis is when you begin accelerating during corner exit. In this situation, steering input, vehicle acceleration, and centrifugal cornering forces are all generated on a tire. For this scenario, minimizing body deflection, having smooth suspension movement and immediate turn-in response is key. The delay experienced from initial turn-in not only hinders the car's reaction, but also removes the feeling that the front wheels are connected to the steering wheel. 

Too Much Body Rigidity

Enhanced body rigidity can provide its benefits to your suspension and tire if the appropriate amount is used. However in some cases, adding increased bracing may have little to no effect if your suspension and tire are not up to par (correctly matched), and in some case can even make your vehicle handle worse. If the tire you are using is inadequate, you may find that the grip threshold available will be much lower. In our previous scenarios, the chassis was the weakest link, but having adequate body rigidity, suspension with an inadequate tire creates a new problem. It is important to find the correct balance in the "closed loop" in order to maximize your tire's performance. 

Chassis bracing is available for a variety of vehicles and in different areas of chassis on our webstore from Quality & Engineered brands such as: Autoexe, LegSport and Toyota Technocraft. The next article will cover suspension and suspension tuning. 


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Motion Control Beam - What It Is, And How It Works

Motion Control Beam - What It Is, And How It Works

Motion Control Beams - Enhanced Rigidity Without Added Harshness

The Basic Concept

Before continuing with this article, understand that your car can only handle, accelerate and brake as good as your tire's performance allows.

Most modern cars have begun utilizing a chassis which has been constructed from high strength steel or alloy, providing high torsional rigidity. Although these bodies are much stiffer than ones of past years, it may not be up to the standard of those who are looking for increased performance. For those customers who seek a more "connected" chassis, body bracing such as a cross-member brace and/or strut tower brace may seem to be an easy, one-and-done solution. Yet in the case of newer cars which already come with a rigid chassis, you may find that the downside of using such bracing on these cars can result in unwanted vibrations. 

The chassis of the car acts as a collection of many springs, as the vehicle body is constantly subjected to vibrations and distortion through braking, acceleration, and suspension forces. If we take a look at standard vehicle suspension, you can see that it consists of a coil spring with a gas or oil filled damper. The car's chassis acts as the coil spring, but what acts as a damper (absorption of applied force)?


In truth, there is no true "damper" for the chassis fitted from the factory. Since there is no damper system, the vibrations transmitted to the chassis are allowed to continue. Motion Control Beams (MCB) are designed to dampen these vibrations though a simple mechanism consisting of two units, with one running across the front of the car and one at the rear.

The outer construction of the MCB is rather simple, and consists of a long torsion bar attached to a damper. Each side of the motion control beam is securely attached to the vehicle's chassis with brackets. In simple form, if the damper component is removed from the motion control beam, it would essentially become a torsion bar attached to two point at the car's chassis, making it no different than a standard body brace. With just the bar alone, the chassis would be stiffened but would provide increased noise, vibration and harshness (NVH) to the vehicle. With the damper component involved, the MCB serves as a dual purpose tool - not only does it dampen chassis vibrations, but you'll also see the benefits of a more connected chassis thanks to the connected points on the chassis. 

Inside A Motion Control Beam

Motion Control Beams can be had as a purely mechanical unit or with nitrogen gas/oil filled internals. Performance will vary depending on the vehicle and the damper type. 

Mechanical Type

The mechanical damper type uses a two-stage damping system which consists of a primary disc spring and friction plate. The telescoping movement from the torsion bar is intercepted by the disc spring, taking care of larger motions and vibrations. The movement of the spring creates micro-vibrations which are quelled by the friction plate. Constructed from stiff resin, the friction plate rubs against the inner damper casing, eliminating the micro-vibrations. The purely mechanical MCB is highly rigid and provides performance similar to a solid beam without the vibration. 

Nitrogen gas/Oil filled type

The Nitrogen gas/Oil filled MCB also uses a two-stage damping system, however this consists of a combination of pressurized Nitrogen gas and shock oil. The primary damping takes place through a piston attached to the main damper shaft/torsion beam, which moves back and forth between two chambers of shock oil. A second piston separates the oil from the nitrogen gas, which is pressurized at 2MPa. 

MCBs which are purchased from Toyota Technocraft and Autoexe are the mechanical type, whereas SYMS Racing/STI MCBs use the nitrogen gas/oil filled type. 
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