Suspension Info...
18-Apr-2006, 10:07 AM
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Suspension Info...
*Part 2 - Suspension Tech!
For those who dont know the suspension facts as well as others maybe this info will be able help you understand the facts of a suspension...
CAMBER: Camber is the angle the wheel deviates from perfectly vertical when looked at from straight ahead. Positive camber would have the top of the wheel inclined outwards, away from vehicle center, while negative camber has the top of the wheel leaning inwards to vehicle center. Contrary to popular belief, any and all camber angles hurt tire adhesion to the road, and for one obvious reason. Tires create the most grip when they put the biggest footprint onto the pavement possible, and any significant camber angles shrink the all important contact patch. The reason people associate negative cmaber with good handling is because as body roll occurs in a corner, positive camber is naturally imparted to the outside wheels. The suspension's camber angle at static ride height (plus it's camber curve, see below) will determine whether the wheel goes into positive camber during body roll, or simply balances out to zero camber. So just know that ideally we want zero camber at all times, but like most things automotive a compromise must be struck: dial in a bit of negative camber at static ride height for the least amount of positive camber possible at maximum effort cornering.
CAMBER CURVE: A camber curve is created by most suspensions because camber constantly changes as the suspension is compressed and expanded. Generally speaking, any independent suspension will increase negative wheel camber as it compresses, and increase positive wheel camber as it expands. Hence, the camber curve lets us see what camber angle the wheel will be at with the suspension at a given amount of compression or expansion.
CASTER: Caster is the angle of inclination between the mounting point of the spindle at hub center to the upper A arm (in cars with upper A arms anyways), when veiwed from the side of the car. If you drew a vertical line through the hub center, then another from this point to the spindle's mounting point on the upper A arm, you would get rearward biased angle on any car (called positive caster angle). This design concept is critical for high speed directional vehicle stability, camber gain during steering, and also plays a roll in anti-dive characteristics under braking.
TOE: Toe is the amount the tire's point inward or outward from dead ahead when the steering is perfectly centered (viewed from directly above the tire). Toe is measured in inches (usually very small increments of inches to be exact); toe-out indicates the wheels point slightly away from vehicle center in a straight on path, while toe-in indicates a slight bias towards vehicle center. Zero toe would be a case where the wheels point dead ahead when the steering is centered. Toe plays an important part in straight line stability and vehicle turn-in characteristics. Toe-in gives makes the car easier to keep pointed straight during normal driving and under heavy braking, while toe-out makes the vehicle feel more eager to enter corners but will cause directional stability to suffer (and stability under braking to suffer greatly).
TOE CURVE: Just like camber, toe amount changes as the suspension undergoes movement. Suspension designers generally take full advantage of this and design the suspension to take on reduce toe amounts as the suspension compresses, thus allowing the vehicle to remain directionally stable during normal driving yet more eager to change direction under braking.
SET BACK: Measures the difference between wheel location from one side to the other relative to each other (when viewed from above). Let's say we were to draw a line through the center of the car (from fore to aft), then draw a line perpendicular to this beginning at the leading edge of, say, the left front tire. If the right front tire didn't precisely touch that line (let's say for simplicity it was 1/4" behind that line), you would have a front axle set back of 1/4". Basically this just tells you how dead on the front wheels are located relative to each other when viewed from the side of a car on an alignment machine. If the set back were a fairly large value (say nearly 1/2-1"), it's probable that something in the suspension or frame has been bent.
SAI (Steering Axis Inclination): This is a measure of the steering's pivot axis vs. the tire's true pivoting axis (as viewed from the front of the car). Virtually every suspension design doesn't actually have the steering system pivot the wheel in a perfectly vertical axis, because the mounting point of the steering's tie rod to the spindle is usually further out from the center of the vehicle than the upper mounting location of the spindle to the upper A arm (in your suspension). In other words, the steering system pivots about an axis that is tilted inwards towards the center of the car at it's upper mounting location. However, the wheel pivots about an axis that is perpendicular to the ground (imagine a second line drawn vertically though the center of the hub). The difference in angle of these two lines, one being the steering axis and the other being the wheel axis, is called the SAI. Whenever the SAI is out of spec, it's usually due to a bent suspension component, as this concept is centered around suspension hard parts and their mounting points to the chassis of the car.
INCLUDED ANGLE: Ok, so I lied! When I said the wheel pivots about an axis perpendicular to the ground, I wasn't being perfectly accurate for most any independent suspension design. Our wheels almost always have a camber angle (hopefully a small negative angle at normal ride height), and this throws off our nice little concept of SAI. To get a really accurate idea of the difference in pivoting axes between the steering system and wheel, you need to take into account the camber of said wheel. So, say if you had an SAI of 15 degrees and a negative camber on the wheel of 1 degree, you would get an included angle of 14 degrees. The wheel is canted inwards 1 degree from our previous true vertical measuring point, so this concept will give us a truly accurate idea of the angles everything will be pivoting on at normal ride height.
SCRUB RADIUS: The difference between where the SAI line and the vertical wheel centerline intersect the ground (as viewed from the front of the car). A vehicle is said to have a postive scrub radius if the SAI line falls closer to vehicle center than the tire, and a negative scrub radius if it falls outside the tire centerline. Scrub radius is important to both vehicle stability under braking and acceleration, plus steering feedback during at the limit adhesion. A negative scrub radius hurts steering feel (most fwd cars have either zero to negative scrub), but keeps the steering wheel from yanking around when one of the steered wheels loses traction (a positive scrub radius can yank the wheel out of your hands when only one steering wheel loses traction during a turn, which is of course a bad thing).
ACKERMAN STEERING: A design concept which allows the inside wheel of the steered axle to travel a tighter arc than the outside. When one thinks about a vehicle turning, it becomes obvious that for the front end to maintain optimal traction, the inside wheel in the turn always has to be making a slightly sharper turn than the inside wheel. If both turned an equal path, the two tires would effectively be following different curves around the same point and wasting a whole lot of grip in the process. So ackerman steering geometry is created to allow the inside wheel to turn a somewhat tighter arc than the outside, maximizing traction during a turn. Also, increased ackerman will enhance toe-out during cornering, allowing the vehicle to become even more nimble in changing direction. Ackerman is however, one of those things the average Honda enthusiast never need worry about, I just figured I would mention it since we are on the topic of aligment.
COIL SPRING: Since almost every car uses coil springs these days, you don't need to know about anything else. A coil spring is exactly that, a coil of wire that takes a certain amount of energy to compress and expand. The energy it takes to compress the spring is what determines the srping rate, which is usually described in lbs/in or in kg/mm. A spring that is decribed as having a rate of 300 lbs/in takes 300 pounds of force to compress it 1 inch.
LINEAR VS. PROGRESSIVE RATE COIL SPRINGS: A linear spring has a straight compression rating, meaning that for our earlier example it would take 300 lbs of force to compress the spring every inch throughout it's total travel. Say the car weighs 300 lbs at one corner, well the spring at that corner would be compressed one inch once installed. For each additional 300 lbs of pressure put on the spring, it would compress an aditional inch until it reaches minimum height. If the spring is termed progressive rate however, this rate changes as the spring is compressed. Many springs are progressive rate because it allows the suspension to be softer initially (making ride quality better) but stiffening up as the amount the spring is compressed increases. This allows you to make the spring fairly soft at smaller compression while making it stiff enough at bigger compression amounts to accurately control wheel & suspension movement when you are hauling ***. Progessive springs usually allow the car to ride & handle better if they are properly designed, but the added complexity to designing and making them work properly also increases the possibility of screwing things up. For these reasons linear springs are often still used for our cars, but if you can find good progressive rate springs from a reputable manufacturer they will enhance both ride quality and handling.
SHOCK ABSORBER: This is what controls spring movement. What is almost always used on our cars are mono-tube hydrolic shocks, so you don't need to know about anything else. A shock absorber's job is to absorb shock (duh!), which means that it dissipates spring energy. Hydrolic shocks do this by moving a small piston with orifices in it through a viscous oil, providing the energy damping needed to control spring movement. The size of the orifices determines the resistance to movement the shock will have, and adjustable shocks have adjustable sized orifices to offer a range of resistance to motion. Since a car's coil spring can be likened to a big slinky, you can imagine that the same way a slinky bounces off one step and jumps to another, where it compresses again and then jumps away once more. A spring will do this just the same, causing the suspension to compress & rebound over and over again after hitting a single bump. The primary job of the shock absorber is to prevent this cycle, and if it's properly matched to the spring's rate it will only allow this to happen once. This is what keeps the tire in good contact with the ground, so you can imagine the importance of getting the shock stiffness right for your springs. The secondary job of the shock is to add some resistance to motion in the suspension, much like the spring does. There's no need to get deep into that yet, just know the shock has an effect on both ride quality and performance.
ADJUSTABLE SHOCK ABSORBER: Adjustable shocks allow you to change their stiffness. Now that you know how important it is to match the shock settings to the spring in order to keep the tire in good contact with the ground, you can also understand how it's control over the spring movement will affect ride quality. Since the shock absorber has some level of control over how quickly the suspension can be compressed (because it adds additional resistance to the whole system), you can imagine that making the shock stiffer will have the same overall effect on ride quality as stiffening the spring. There are two main types of adjustable shocks: those that adjust stiffness of the compression stroke only and those that adjust stiffness on both compression and rebound strokes. It's not important to go over the different types of desgins here, but know that most shocks either only adjust compression stiffness (called single-adjustable shocks) or they adjust both compression & rebound at the same time (called double-adjustable shocks). This means that there is no way to adjust the bias between compression & rebound stiffness on double-adjustables, which is of principle design concern to shock manufacturers because it's so easy to get the bias wrong. There are indepently double-adjustable shocks which allow you to change this bias, but I wouldn't recommend them for the average enthusiast. You will probably just end up making the suspension damping worse than it was stock. Recommendations here are usually to get the double adjustable shocks that control both compression & rebound (but not independently), and that's probably the best idea for the average enthusiast.
COILOVER SUSPENSION: A coilover suspension is simply one that has the shock body located within the space inside the coil spring (as installed on the car). This is the best design possible because the shock is moving in the same plane as the spring, which ensures that it can most accurately control spring movement, plus it's usually the lightest. In our double wishbone suspension systems, the shock's only job is to control spring movement, so it makes sense that Honda equips all of their performance cars with coilover systems. The popular catch phrase "coilover" is only applied to systems that are sold complete with both shocks & springs (and sometimes upper mounts), but the truth is that every spring or shock you install on the car will function in a coilover system. Here's the basic breakdown as far as you are concerned: Honda uses almost exclusively the coilover setup on their current cars. Aftermarket spring manufacturers like Ground Control simply one-up their design by adding height adjustability to the system. This comes in the form of threaded shock bodies and adjustable spring perches, we generally refer to them as "sleeved springs". There are also shock manufacturers like Koni who one-up Honda in the shock absorber department by offering adjustable shocks, which are adjusted usually by a **** somewhere on the shock body or rod. Then at the top shelf of coilover designs, you have companies like Tein who one-up everybody else by offering a complete & ready to install coilover package that is adjustable in several different ways (height adjust, rebound adjust, compression adjust, whatever they throw in) and comes as a properly matched system. These are the systems we refer to as "true" or "complete" coilovers. Usually these shocks are rebuildable and offer custom valving options, and the company usually has a variety of spring rates available for you. If these are the best systems, it's simply because they are the most complete. The only system that offers a better garaunteed match between spring & shock are usually the stock units (which of course are not stiff enough and have no adjustability). What I am getting at here is that just because you get springs from one manufacturer and shocks from another does not mean that you won't have a kickass ride, it just means that there is more possiblity of mismatching one part to another. As we have pointed out many times, the simple Eibach Pro Kit & Koni adj. shocks combo seems to whoop *** on many other street setups without costing an arm and a leg (relatively speaking).
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How do sway bars work, and how can you use them to tune your car’s suspension?
Most performance people know that stiffer rear sway bars reduce the understeering tendencies of a vehicle, but if you ask them exactly why this is they generally draw a blank. Usually they know the results, but not the reasons behind chassis tuning. This article is intended to answer those questions as well as give readers a better understanding of what goes on in your suspension when you take a corner. First, let's get an understanding of what lateral weight transfer is, because this will help you understand exactly how sway bars work to tune the balance of the chassis.
Lateral weight transfer is a function of three things:
-overall weight of car
-height of the Cg (center of gravity)
-track width (this is the distance between the vertical centerlines of each tire on an axle, and many times track width is different on each axle)
So the first thing to notice here is that spring rate IS NOT a primary determinate in how much weight is transferred laterally on a car for a given amount of steering input. This is something many people have a hard time swallowing, but nevertheless it is true. All the springs primarily do is determine how much the suspension will compress or expand due to this weight transfer.
BODY ROLL, So why is body roll bad?
Two reasons:
Next, you need to know that the principle way you control body roll is through spring rates. And here's where we encounter the problem of not being able to change the static spring rates between cornering maneuvers and just going straight. To show a quick example of this:
- Say the amount of body roll during a corner is 10 degrees for a spring rate of 500 lbs. If you wanted to halve this amount of roll, you would need to roughly double the spring rate to accomplish it. Now we already know that limiting body roll can improve handling (depending on circumstances and suspension setup), but running a spring that stiff will cause the car to be so bouncy that the tire will rarely be in good contact with the ground, unless the road is perfectly smooth. So how can we selectively increase spring rates only under cornering so that our straight line stability & tire to road contact is not compromised by really stiff springs? The sway bar is the answer.
Now it should be stated here what sway bars essentially do, even though I know you may already know this. What a sway bar does is counteract the action of body roll during cornering by transferring spring rate from the inside wheel to the outside wheel in a corner. This means that you don't actually get any added spring rate; you just subtract it from one side and add it to the other. This has the ultimate effect of transferring load from the inside tire to the outside, which has the visual effect of compressing the suspension on the inside of the turn and expanding the suspension on the outside of the turn (thus limiting body roll). This is good mainly because it smoothes the speed of weight transfer during quick transitions and also limits the camber change experienced at the corners of the car through suspension travel. And of course, using this concept one can dial in the amount of total loading on the outside tire by varying the effectiveness of the sway bar (stiffer bars equal more transfer). And the beauty of all this is that it mostly only occurs during cornering, so our straight line spring rates are not affected. The other thing Ok, so hopefully now you all understand this concept. This is the most important part though, so if anything is still fuzzy read this again until you get it. Also, here's an example of how this works:
-For this example we will use a sway bar with a roll stiffness of 250 lbs.
Left front static load: 1000lbs
Right front static load: 1000lbs
-lateral weight transfer in a right hand turn
Left front: + 500lbs
Right front: - 500lbs
Total weight transfer: 1000lbs
-load transfer of sway bar(which is 250 lbs):
Left front: +250lbs
Right front: -250lbs
Total weight transfer: 1000lbs
-total effective cornering load for this example:
Left front: 1000 + 750= 1750lbs
Right front: 1000 - 750= 250lbs
-without sway bar
Left front: 1000 + 500= 1500lbs
Right front: 1000 - 500= 500lbs
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Alright, now we are coming into the home stretch of this learning curve. You need to know that although you cannot control the total amount of lateral weight transfer during cornering (as I stated earlier), you CAN have some control over how it is distributed on each axle. Looking at the above example, you see that with or without the sway bar involved, total weight transfer change is always 1000 lbs. You can't change this amount, but you can re-distribute it along the axle. And this is a function of spring rates entirely, which we now know is best controlled during cornering through the use of sway bars.
So how does one control the balance of a car when armed with this knowledge? It's actually very simple at this point, if you understand that increasing tire loading adds to the total amount of traction available from it, but this relationship is NOT linear. The more load on the tire, the more traction available, but the amount of traction gained diminishes as load increases. So at first it's almost a direct "you add 250lbs of load, you get 250lbs of extra traction", but at 1000lbs of load, you might only get 800lbs of extra traction. Knowing this, look at the example I gave of the sway bar at work. Since it transfers load away from the inside tire, you lose traction there. Although it transfers this load to the outside tire, it is already quite loaded and therefore the 250lbs of load will not increase overall traction by 250lbs. More like maybe 150lbs. Now the inside tire, being much less loaded, could have gained more like 220lbs or traction from the 250lbs of load. So look at what we have in the end: although the outside tires already do most of the work, adding a sway bar actually lowers the total amount of traction available at this end of the car by increasing the difference in load distribution. And the stiffer that sway bar is, the more it will limit the total traction available at that end.
So, to make a really long post short (again, sorry), what we end up with is the knowledge that weight transfer ultimately lowers the total amount of traction available at each end of the car. This is why the more we can limit total weight transfer (by increasing track, lowering the Cg height, or lowering overall vehicle weight) the more total traction will be available. But for the purposes of this post, we are explaining how sway bar sizing (which directly reflects it's roll stiffness amount) cures an unbalanced car. If a car is understeering, it's because the rear end has more total traction than the front. If you put a big sway bar on the rear suspension to limit the total amount of traction available there (by maximizing the amount of load transfer to the outside wheel), you can dial it in to match the front suspension's total available traction. And when we get really smart, we start to match the front & rear bars to one another to achieve the best balance through the largest possible range of suspension movement.
If i missed anything please add to it.
For those who dont know the suspension facts as well as others maybe this info will be able help you understand the facts of a suspension...
CAMBER: Camber is the angle the wheel deviates from perfectly vertical when looked at from straight ahead. Positive camber would have the top of the wheel inclined outwards, away from vehicle center, while negative camber has the top of the wheel leaning inwards to vehicle center. Contrary to popular belief, any and all camber angles hurt tire adhesion to the road, and for one obvious reason. Tires create the most grip when they put the biggest footprint onto the pavement possible, and any significant camber angles shrink the all important contact patch. The reason people associate negative cmaber with good handling is because as body roll occurs in a corner, positive camber is naturally imparted to the outside wheels. The suspension's camber angle at static ride height (plus it's camber curve, see below) will determine whether the wheel goes into positive camber during body roll, or simply balances out to zero camber. So just know that ideally we want zero camber at all times, but like most things automotive a compromise must be struck: dial in a bit of negative camber at static ride height for the least amount of positive camber possible at maximum effort cornering.
CAMBER CURVE: A camber curve is created by most suspensions because camber constantly changes as the suspension is compressed and expanded. Generally speaking, any independent suspension will increase negative wheel camber as it compresses, and increase positive wheel camber as it expands. Hence, the camber curve lets us see what camber angle the wheel will be at with the suspension at a given amount of compression or expansion.
CASTER: Caster is the angle of inclination between the mounting point of the spindle at hub center to the upper A arm (in cars with upper A arms anyways), when veiwed from the side of the car. If you drew a vertical line through the hub center, then another from this point to the spindle's mounting point on the upper A arm, you would get rearward biased angle on any car (called positive caster angle). This design concept is critical for high speed directional vehicle stability, camber gain during steering, and also plays a roll in anti-dive characteristics under braking.
TOE: Toe is the amount the tire's point inward or outward from dead ahead when the steering is perfectly centered (viewed from directly above the tire). Toe is measured in inches (usually very small increments of inches to be exact); toe-out indicates the wheels point slightly away from vehicle center in a straight on path, while toe-in indicates a slight bias towards vehicle center. Zero toe would be a case where the wheels point dead ahead when the steering is centered. Toe plays an important part in straight line stability and vehicle turn-in characteristics. Toe-in gives makes the car easier to keep pointed straight during normal driving and under heavy braking, while toe-out makes the vehicle feel more eager to enter corners but will cause directional stability to suffer (and stability under braking to suffer greatly).
TOE CURVE: Just like camber, toe amount changes as the suspension undergoes movement. Suspension designers generally take full advantage of this and design the suspension to take on reduce toe amounts as the suspension compresses, thus allowing the vehicle to remain directionally stable during normal driving yet more eager to change direction under braking.
SET BACK: Measures the difference between wheel location from one side to the other relative to each other (when viewed from above). Let's say we were to draw a line through the center of the car (from fore to aft), then draw a line perpendicular to this beginning at the leading edge of, say, the left front tire. If the right front tire didn't precisely touch that line (let's say for simplicity it was 1/4" behind that line), you would have a front axle set back of 1/4". Basically this just tells you how dead on the front wheels are located relative to each other when viewed from the side of a car on an alignment machine. If the set back were a fairly large value (say nearly 1/2-1"), it's probable that something in the suspension or frame has been bent.
SAI (Steering Axis Inclination): This is a measure of the steering's pivot axis vs. the tire's true pivoting axis (as viewed from the front of the car). Virtually every suspension design doesn't actually have the steering system pivot the wheel in a perfectly vertical axis, because the mounting point of the steering's tie rod to the spindle is usually further out from the center of the vehicle than the upper mounting location of the spindle to the upper A arm (in your suspension). In other words, the steering system pivots about an axis that is tilted inwards towards the center of the car at it's upper mounting location. However, the wheel pivots about an axis that is perpendicular to the ground (imagine a second line drawn vertically though the center of the hub). The difference in angle of these two lines, one being the steering axis and the other being the wheel axis, is called the SAI. Whenever the SAI is out of spec, it's usually due to a bent suspension component, as this concept is centered around suspension hard parts and their mounting points to the chassis of the car.
INCLUDED ANGLE: Ok, so I lied! When I said the wheel pivots about an axis perpendicular to the ground, I wasn't being perfectly accurate for most any independent suspension design. Our wheels almost always have a camber angle (hopefully a small negative angle at normal ride height), and this throws off our nice little concept of SAI. To get a really accurate idea of the difference in pivoting axes between the steering system and wheel, you need to take into account the camber of said wheel. So, say if you had an SAI of 15 degrees and a negative camber on the wheel of 1 degree, you would get an included angle of 14 degrees. The wheel is canted inwards 1 degree from our previous true vertical measuring point, so this concept will give us a truly accurate idea of the angles everything will be pivoting on at normal ride height.
SCRUB RADIUS: The difference between where the SAI line and the vertical wheel centerline intersect the ground (as viewed from the front of the car). A vehicle is said to have a postive scrub radius if the SAI line falls closer to vehicle center than the tire, and a negative scrub radius if it falls outside the tire centerline. Scrub radius is important to both vehicle stability under braking and acceleration, plus steering feedback during at the limit adhesion. A negative scrub radius hurts steering feel (most fwd cars have either zero to negative scrub), but keeps the steering wheel from yanking around when one of the steered wheels loses traction (a positive scrub radius can yank the wheel out of your hands when only one steering wheel loses traction during a turn, which is of course a bad thing).
ACKERMAN STEERING: A design concept which allows the inside wheel of the steered axle to travel a tighter arc than the outside. When one thinks about a vehicle turning, it becomes obvious that for the front end to maintain optimal traction, the inside wheel in the turn always has to be making a slightly sharper turn than the inside wheel. If both turned an equal path, the two tires would effectively be following different curves around the same point and wasting a whole lot of grip in the process. So ackerman steering geometry is created to allow the inside wheel to turn a somewhat tighter arc than the outside, maximizing traction during a turn. Also, increased ackerman will enhance toe-out during cornering, allowing the vehicle to become even more nimble in changing direction. Ackerman is however, one of those things the average Honda enthusiast never need worry about, I just figured I would mention it since we are on the topic of aligment.
COIL SPRING: Since almost every car uses coil springs these days, you don't need to know about anything else. A coil spring is exactly that, a coil of wire that takes a certain amount of energy to compress and expand. The energy it takes to compress the spring is what determines the srping rate, which is usually described in lbs/in or in kg/mm. A spring that is decribed as having a rate of 300 lbs/in takes 300 pounds of force to compress it 1 inch.
LINEAR VS. PROGRESSIVE RATE COIL SPRINGS: A linear spring has a straight compression rating, meaning that for our earlier example it would take 300 lbs of force to compress the spring every inch throughout it's total travel. Say the car weighs 300 lbs at one corner, well the spring at that corner would be compressed one inch once installed. For each additional 300 lbs of pressure put on the spring, it would compress an aditional inch until it reaches minimum height. If the spring is termed progressive rate however, this rate changes as the spring is compressed. Many springs are progressive rate because it allows the suspension to be softer initially (making ride quality better) but stiffening up as the amount the spring is compressed increases. This allows you to make the spring fairly soft at smaller compression while making it stiff enough at bigger compression amounts to accurately control wheel & suspension movement when you are hauling ***. Progessive springs usually allow the car to ride & handle better if they are properly designed, but the added complexity to designing and making them work properly also increases the possibility of screwing things up. For these reasons linear springs are often still used for our cars, but if you can find good progressive rate springs from a reputable manufacturer they will enhance both ride quality and handling.
SHOCK ABSORBER: This is what controls spring movement. What is almost always used on our cars are mono-tube hydrolic shocks, so you don't need to know about anything else. A shock absorber's job is to absorb shock (duh!), which means that it dissipates spring energy. Hydrolic shocks do this by moving a small piston with orifices in it through a viscous oil, providing the energy damping needed to control spring movement. The size of the orifices determines the resistance to movement the shock will have, and adjustable shocks have adjustable sized orifices to offer a range of resistance to motion. Since a car's coil spring can be likened to a big slinky, you can imagine that the same way a slinky bounces off one step and jumps to another, where it compresses again and then jumps away once more. A spring will do this just the same, causing the suspension to compress & rebound over and over again after hitting a single bump. The primary job of the shock absorber is to prevent this cycle, and if it's properly matched to the spring's rate it will only allow this to happen once. This is what keeps the tire in good contact with the ground, so you can imagine the importance of getting the shock stiffness right for your springs. The secondary job of the shock is to add some resistance to motion in the suspension, much like the spring does. There's no need to get deep into that yet, just know the shock has an effect on both ride quality and performance.
ADJUSTABLE SHOCK ABSORBER: Adjustable shocks allow you to change their stiffness. Now that you know how important it is to match the shock settings to the spring in order to keep the tire in good contact with the ground, you can also understand how it's control over the spring movement will affect ride quality. Since the shock absorber has some level of control over how quickly the suspension can be compressed (because it adds additional resistance to the whole system), you can imagine that making the shock stiffer will have the same overall effect on ride quality as stiffening the spring. There are two main types of adjustable shocks: those that adjust stiffness of the compression stroke only and those that adjust stiffness on both compression and rebound strokes. It's not important to go over the different types of desgins here, but know that most shocks either only adjust compression stiffness (called single-adjustable shocks) or they adjust both compression & rebound at the same time (called double-adjustable shocks). This means that there is no way to adjust the bias between compression & rebound stiffness on double-adjustables, which is of principle design concern to shock manufacturers because it's so easy to get the bias wrong. There are indepently double-adjustable shocks which allow you to change this bias, but I wouldn't recommend them for the average enthusiast. You will probably just end up making the suspension damping worse than it was stock. Recommendations here are usually to get the double adjustable shocks that control both compression & rebound (but not independently), and that's probably the best idea for the average enthusiast.
COILOVER SUSPENSION: A coilover suspension is simply one that has the shock body located within the space inside the coil spring (as installed on the car). This is the best design possible because the shock is moving in the same plane as the spring, which ensures that it can most accurately control spring movement, plus it's usually the lightest. In our double wishbone suspension systems, the shock's only job is to control spring movement, so it makes sense that Honda equips all of their performance cars with coilover systems. The popular catch phrase "coilover" is only applied to systems that are sold complete with both shocks & springs (and sometimes upper mounts), but the truth is that every spring or shock you install on the car will function in a coilover system. Here's the basic breakdown as far as you are concerned: Honda uses almost exclusively the coilover setup on their current cars. Aftermarket spring manufacturers like Ground Control simply one-up their design by adding height adjustability to the system. This comes in the form of threaded shock bodies and adjustable spring perches, we generally refer to them as "sleeved springs". There are also shock manufacturers like Koni who one-up Honda in the shock absorber department by offering adjustable shocks, which are adjusted usually by a **** somewhere on the shock body or rod. Then at the top shelf of coilover designs, you have companies like Tein who one-up everybody else by offering a complete & ready to install coilover package that is adjustable in several different ways (height adjust, rebound adjust, compression adjust, whatever they throw in) and comes as a properly matched system. These are the systems we refer to as "true" or "complete" coilovers. Usually these shocks are rebuildable and offer custom valving options, and the company usually has a variety of spring rates available for you. If these are the best systems, it's simply because they are the most complete. The only system that offers a better garaunteed match between spring & shock are usually the stock units (which of course are not stiff enough and have no adjustability). What I am getting at here is that just because you get springs from one manufacturer and shocks from another does not mean that you won't have a kickass ride, it just means that there is more possiblity of mismatching one part to another. As we have pointed out many times, the simple Eibach Pro Kit & Koni adj. shocks combo seems to whoop *** on many other street setups without costing an arm and a leg (relatively speaking).
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How do sway bars work, and how can you use them to tune your car’s suspension?
Most performance people know that stiffer rear sway bars reduce the understeering tendencies of a vehicle, but if you ask them exactly why this is they generally draw a blank. Usually they know the results, but not the reasons behind chassis tuning. This article is intended to answer those questions as well as give readers a better understanding of what goes on in your suspension when you take a corner. First, let's get an understanding of what lateral weight transfer is, because this will help you understand exactly how sway bars work to tune the balance of the chassis.
Lateral weight transfer is a function of three things:
-overall weight of car
-height of the Cg (center of gravity)
-track width (this is the distance between the vertical centerlines of each tire on an axle, and many times track width is different on each axle)
So the first thing to notice here is that spring rate IS NOT a primary determinate in how much weight is transferred laterally on a car for a given amount of steering input. This is something many people have a hard time swallowing, but nevertheless it is true. All the springs primarily do is determine how much the suspension will compress or expand due to this weight transfer.
BODY ROLL, So why is body roll bad?
Two reasons:
Next, you need to know that the principle way you control body roll is through spring rates. And here's where we encounter the problem of not being able to change the static spring rates between cornering maneuvers and just going straight. To show a quick example of this:
- Say the amount of body roll during a corner is 10 degrees for a spring rate of 500 lbs. If you wanted to halve this amount of roll, you would need to roughly double the spring rate to accomplish it. Now we already know that limiting body roll can improve handling (depending on circumstances and suspension setup), but running a spring that stiff will cause the car to be so bouncy that the tire will rarely be in good contact with the ground, unless the road is perfectly smooth. So how can we selectively increase spring rates only under cornering so that our straight line stability & tire to road contact is not compromised by really stiff springs? The sway bar is the answer.
Now it should be stated here what sway bars essentially do, even though I know you may already know this. What a sway bar does is counteract the action of body roll during cornering by transferring spring rate from the inside wheel to the outside wheel in a corner. This means that you don't actually get any added spring rate; you just subtract it from one side and add it to the other. This has the ultimate effect of transferring load from the inside tire to the outside, which has the visual effect of compressing the suspension on the inside of the turn and expanding the suspension on the outside of the turn (thus limiting body roll). This is good mainly because it smoothes the speed of weight transfer during quick transitions and also limits the camber change experienced at the corners of the car through suspension travel. And of course, using this concept one can dial in the amount of total loading on the outside tire by varying the effectiveness of the sway bar (stiffer bars equal more transfer). And the beauty of all this is that it mostly only occurs during cornering, so our straight line spring rates are not affected. The other thing Ok, so hopefully now you all understand this concept. This is the most important part though, so if anything is still fuzzy read this again until you get it. Also, here's an example of how this works:
-For this example we will use a sway bar with a roll stiffness of 250 lbs.
Left front static load: 1000lbs
Right front static load: 1000lbs
-lateral weight transfer in a right hand turn
Left front: + 500lbs
Right front: - 500lbs
Total weight transfer: 1000lbs
-load transfer of sway bar(which is 250 lbs):
Left front: +250lbs
Right front: -250lbs
Total weight transfer: 1000lbs
-total effective cornering load for this example:
Left front: 1000 + 750= 1750lbs
Right front: 1000 - 750= 250lbs
-without sway bar
Left front: 1000 + 500= 1500lbs
Right front: 1000 - 500= 500lbs
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Alright, now we are coming into the home stretch of this learning curve. You need to know that although you cannot control the total amount of lateral weight transfer during cornering (as I stated earlier), you CAN have some control over how it is distributed on each axle. Looking at the above example, you see that with or without the sway bar involved, total weight transfer change is always 1000 lbs. You can't change this amount, but you can re-distribute it along the axle. And this is a function of spring rates entirely, which we now know is best controlled during cornering through the use of sway bars.
So how does one control the balance of a car when armed with this knowledge? It's actually very simple at this point, if you understand that increasing tire loading adds to the total amount of traction available from it, but this relationship is NOT linear. The more load on the tire, the more traction available, but the amount of traction gained diminishes as load increases. So at first it's almost a direct "you add 250lbs of load, you get 250lbs of extra traction", but at 1000lbs of load, you might only get 800lbs of extra traction. Knowing this, look at the example I gave of the sway bar at work. Since it transfers load away from the inside tire, you lose traction there. Although it transfers this load to the outside tire, it is already quite loaded and therefore the 250lbs of load will not increase overall traction by 250lbs. More like maybe 150lbs. Now the inside tire, being much less loaded, could have gained more like 220lbs or traction from the 250lbs of load. So look at what we have in the end: although the outside tires already do most of the work, adding a sway bar actually lowers the total amount of traction available at this end of the car by increasing the difference in load distribution. And the stiffer that sway bar is, the more it will limit the total traction available at that end.
So, to make a really long post short (again, sorry), what we end up with is the knowledge that weight transfer ultimately lowers the total amount of traction available at each end of the car. This is why the more we can limit total weight transfer (by increasing track, lowering the Cg height, or lowering overall vehicle weight) the more total traction will be available. But for the purposes of this post, we are explaining how sway bar sizing (which directly reflects it's roll stiffness amount) cures an unbalanced car. If a car is understeering, it's because the rear end has more total traction than the front. If you put a big sway bar on the rear suspension to limit the total amount of traction available there (by maximizing the amount of load transfer to the outside wheel), you can dial it in to match the front suspension's total available traction. And when we get really smart, we start to match the front & rear bars to one another to achieve the best balance through the largest possible range of suspension movement.
If i missed anything please add to it.
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