Unofficial Honda FIT Forums - Suspension Theory

If anyone else can find some technical information, especially about lowering springs and how different spring rates (progressive vs. linear, etc. ) work/produce result X, please PM me!

Taken from Suspensions!!! - 8th Generation Honda Civic Forum with OP's (Highrev1) permission.
Also some information taken from TurnFast!.

"Ok the information is back Not going anywhere again either...

“1. There is no "best"...

2. In order to pick what may work best for you're application, you need to take a look at what the car is doing now... cant make improvements if you have no base line to compare it to. So, what’s the car doing now that is unsatisfactory? and is it actually the car thats causing the problem or is it the driver? This means learn how to drive your car to the absolute LIMIT before you modify it!!!!!

3. People tend to recomend what they have or what they've heard is "best" rather then give any sort of usefull info. So be picky as to who you take your advice from. EVEN ME I am heavily biased towards a race oriented setup.

4. You'll probably gain more by picking out the right tire then you would by changing out the suspension.... “

TIRE TRACTION
(from turnfast.com)

Assuming equal horsepower and driver skills, the fastest car around the track will be the one with the most tire traction. Traction aids in acceleration, braking, and cornering.
"Handling" is all about maximizing tire traction. Regardless of how much advanced hardware the car has, the bottom line is that the car's entire braking, accelerating, and cornering performance has to be translated through the four small patches of rubber in contact with the road. Think about it. Ignore absolutely everything about a car except for how much rubber is in contact with the road. Maximizing the performance of these four small patches is what "handling" is all about.
Maximum traction, of course, is affected by the suspension design, the type of tire, it's rubber compound, its contact patch size, and several other factors. Once a given car and tire is selected, there is still the task getting the absolute most out of that specific tire.
After-market products which can help improve tire traction include anti-roll bars, shock tower bars, stiffer springs, adjustable shocks, wheel alignment kits, and others. Used properly, these items are designed to maximize the contact patch of the tire during dynamic conditions. Used improperly, these same components will actually deteriorate traction and handling under race conditions.
Another major factor in tire traction, often overlooked, is the driver. A practiced driver having very smooth control of the car, and high sensitivity to the tire's traction performance can improve the car's lap time as much as just about any single after market hardware modification, and it's free. Give a pro driver your car for a 30 minute session, and he'll likely best your times by an amount you thought impossible.
To do this, the driver must fully understand the tires, how their maximum performance is achieved, and have enough practice time developing a sensitivity to how the tire is performing at any given moment on the track.
Three factors determine the maximum potential grip of a tire: the coefficient of friction provided by its rubber compound (stickier is better), the amount of rubber as determined by the tire size (bigger is better), and the amount of downforce applied to the tire (pushing down adds to the total friction applied). Of course there is a limit to all of these, and a point is reached where more is not better.

Slip Angle
There are two factors in reaching and sustaining the maximum traction performance from the tire. First, a tire's maximum traction potential is actually reached when there is a small amount of slippage. This "slippage" is translated differently for braking, accelerating, and cornering.
Under braking, the peak performance of the tire is reached when the tire is turning slightly less than a one-to-one relationship of the distance traveled. In other words, if the car were at a steady state, and the wheel turned 10 times to cover a certain distance, under braking, the wheel would now turn perhaps only 9-1/2 times to achieve the peak slippage performance. It is possible to learn how to feel the car through the brake pedal, steering wheel, and seat and sense this tiny bit of extra braking force from the tire.
In acceleration, the tire should travel slightly more distance than the distance of the acceleration (spin just a bit faster than normal). The tires will actual slip; not a lot all at once to result in free wheelspin, but ever so slightly during the whole acceleration phase. When you can sense this slip, and control it, this is when you're getting maximum acceleration from the vehicle.
In cornering, this slippage is present when the wheels are actually turned just slightly more than the actual amount required to go the intended path (this difference is an angle and is where we get the term "slip angle" from). To accomplish this slip angle the car must actually be sliding ever so slightly during cornering. Not a big power slide, just a little extra slip. At first, this can feel very uncomfortable, as though you are starting to lose traction. In fact, this is where the car has its greatest traction. The tricky part is approaching this limit and not crossing it. If the car is not sliding at all, then it isn't going fast enough. If it is sliding enough to actually drift (or have noticeable understeer, or oversteer), the tire is being used beyond its limit. The corner speeds will be slower, and the tire will wear out much more quickly.
In each of these cases, we emphasized the "slightly" aspect of this slippage. Too little, and the tire does not reach maximum performance. If the car feels "hooked up on rails," then the car is not being driven fast enough. Until you feel that tiny bit of slip, you can go faster. Knowing how to approach that point without exceeding it takes a great deal of practice. Too much slippage and you'll exceed the tire's limits and the tires slide excessively resulting in locked-up braking, wheel spin in accelerating, excessive sliding during cornering. Ultimately they will overheat, get slippery, and wear out much faster.
The amount of slippage required is different for each tire, but we're talking in the range of 4 to 10 percent. When cornering, the steering angle input is perhaps 5 to 6 degrees more than required to negotiate the turn. However, to keep this from turning the car too much for the corner, it has to be pushed with speed to generate that little bit of slip to compensate. Racing tires will perform best with a little less slippage than a street tire. If you learn to race on a street tire then switch to racing tires, you'll have to learn to back off a little, and be smidgen more gentle with the race tire.
How should this slippage concept affect your driving? If you look at the graphs which illustrate the affect of slippage on traction, you'll see that at the peak traction point, there is actually a pretty wide margin of slip that will generate maximum traction. If you tend to drive in the latter part of that band, you'll acheive good cornering performance, but being closer to the edge the tire's limits, you'll build more heat and generate greater tire wear. The tires will feel great for a while, but they will wear out sooner, and the last several laps in session will have poor performance. If you drive within the earlier part of that peak traction band, your traction performance will remain consistent over a longer period of time. In time trials, you won't see much of a difference (except in replacement tire costs), but in racing, this will put you farther ahead of the competition in longer runs.
A time that you may need to drive in latter part of the traction band is when the track is cold, and you must push the tire harder to keep heat buildup in the tire.

Driving Smoothness & Traction
One more principle to learn. A tire's maximum traction potential will not be realized unless it is brought to that point gradually. This is true of just about everything dealing with frictional traction, and you experience it regularly in everyday occurrences.
Imagine this experiment. Place a piece of paper on a table, and an ordinary breakfast bowl on the paper. Start pulling on the paper slowly, then gradually faster. The bowl remains on the paper and is dragged along with it. Next, yank the paper immediately. It will come out from under the bowl leaving the bowl unmoved, or barely moved. Same bowl, same paper, same table. What was different? The acceleration of the forces applied. In your car, the tires are the paper.
Ease the car smoothly into a corner, and the tire will have a high level of traction. Jerk the steering wheel too quickly, and the tire will not maintain grip with the road. Same car, same tires, same road. The difference is the acceleration of the forces, or the smoothness with which cornering, acceleration, and braking forces are applied. Smoother is grippier.
The principle of driving smoothly is paramount to every factor of improving a car's handling performance. All the hardware in the world will not fix a car with a driver using "jerk and stab" braking, accelerating, and turning control behavior. Inexperienced drivers frequently blame the lack of the greatest hardware in their car for performance problems which are actually caused by their driving style. There's enough stories to suggest even a few pros have this habit. Be honest and analyse your driving, or get an experienced instructor to analyse it for you.
One of the common faults and gripes of new drivers is front end push (understeer) when entering a corner. "Man, my car slides something horrible going through the first half of that turn." There is significant probability that the car is fine, but the driver is braking too late, too hard, and is rushing the turn-in with a sudden steering movement. Brake sooner, let up sooner (and more gradually), and ease into the corner with a larger and smoother radius. This will likely cure the understeering problem, and will most certainly reduce it if suspension setup is an issue.
Smooth driving maximizes tire traction. Maximized tire traction is what leads to fast driving. We repeat -- smoother is grippier.

Mechanical and Aerodynamic Downforce
Another factor which affects tire traction, but one that is not likely to be factor in the weekend racing of your street car is vertical loading -- the combination of mechanical and aerodynamic downforce. Whether applied by mechanical forces (which is essentially gravity), or aerodynamic forces, the total amount of downward push on the tire affects the available traction. To demonstrate, lightly drag a pencil eraser across a table. It slides easily. Now push down on it and drag it. There is much higher friction. Same goes for tires.
This simple demonstration might lead you to believe you should add weight to your car to gain more traction. However, practical experience tells us that lighter cars generally handle better than heavier ones. It turns out that while greater weight on the tires will increase traction potential, it also increases the amount of work they have to do. When cornering, the tire must keep a heavier car on the track, and therefore there are greater lateral forces. If you graph the increase of traction vs. the increase in work based on the increase in weight, the work load increases faster than the traction improvement. So mechanical downforce is not necessarily the way to increase tire traction.
This is where aerodynamics have played such an important role in racing the past couple of decades. Aerodynamic downforce provides that increased push down on the car to increase traction, but that push is not translated into lateral load that the tires have to deal with when cornering. There is increased traction without increased work.

WEIGHT TRANSFER
(from turnfast.com)

A fundamental topic in any discussion about handling is weight transfer. If you do not fully understand weight transfer, you will not be effective in understanding how to adjust the car for maximum handling performance.
Given a certain car weight, there is a certain amount of mechanical downforce applied to each tire. As we stated in the tire traction article, this downforce impacts the grip potential of the tire. While a car is braking, accelerating, or cornering, the effective mechanical downforce on, and therefore the grip of, the tires is constantly changing.
These changes are referred to as "weight transfer." Of course, the weight of the car isn't changing, or moving about the car, but the forces on the tire contact patches are changing due to inertia and momentum. If you were to have a set of scales under the tires while driving, you would see what appears to be a constant changing of the weight at each tire, hence the name.

What does Weight Transfer Do?
Referring to the figures, we have illustrated a street car weighing 3000 lbs, and with a typical FWD street car's weight distribution of 60% front and 40% rear. We'll assume the car's side to side weight distribution is equal. We see that when standing still, the front tires have 900 lbs of weight load, and the rear tires have 600 lbs each.
Anytime the car's direction changes through braking, accelerating, or cornering, each tire will experience a gain or loss of mechanical downforce, such as the examples illustrated. This weight transfer has significant impact on traction. Unfortunately for us, the net sum of the traction of the four tires does not stay equal. What is lost from the unloaded tires is not entirely transferred to the loaded tires. Overall there is a loss in traction.
Because of this, race car design, and some of the modifications you make to your street car, are designed to minimize weight transfer. It cannot be eliminated, but it can be reduced. The more it is reduced, the more traction is retained. By reducing the increase in load on the loaded tires, we can reduce the work they have to do. By reducing the loss of load on the unloaded tires, we retain the traction they can provide.

How can Weight Transfer be Minimized?
Contrary to what you may be inclined to believe, the amount of weight transfer is not altered by springs, shocks, anti-roll bars, etc. Weight transfer is a result of inertia and momentum. These suspension components cannot change that. What these components can do is impact how much the suspension moves in response to the load change, and how quickly the load transfers to the tire contact patches.
The amount of weight transfer is dominated by the vehicle's weight, location of the center of gravity, wheelbase, and track, and the amount of force applied during braking, accelerating, and cornering.
Weight transfer is a function of the vehicle's weight and the forces acting on that weight. Reduce the weight, and ou reduce the product the of the forces involved.
The center of gravity is the fulcrum point through which the vehicle's weight is multiplied by dynamic forces. In particular, the higher the CG point is, the greater the effect of the forces. Reduce the CG height reduces the product of the forces and vehicle weight.
The longer the wheelbase and wider the track in relation to the height of the center of gravity, the more resistance the car has to weight transfer. They behave as counteracting lateral levers to the vertical lever of the center of gravity point.
Another important concept of controlling weight transfer besides minimizing it, is to control where it is transferred. Where weight transfer occurs is related to the static weight distribution of the car, the roll couple distribution of the car, the height of the roll center of the car, and the slope of the roll center in relation to the ground plane.
Roll couple distribution is the relative roll stiffness between the front and rear of the car, and the left and right of the car. In cornering, the front of the car may roll less than the rear of the car. This has impact on how the weight transfer is distributed.
The roll center is the line through which the vehicle rolls. It is not necessarily parallel to the ground. Weight distribution, and roll coupling distribution can create a roll point at the front of the car which is lower to the ground that the roll point of the rear of the car. This creates a sloped line. The angle of this line has influence on how much weight is transferred, and where it goes.

Vehicle Weight Distribution
Modifications which reduce vehicle weight and the location of the center of gravity impact the amount of weight transferred and where it is transferred. Reducing a vehicle's total weight reduces the amount of weight transfer. Redistributing that weight front & rear, or side to side will change how that weight transfer is distributed among the four tires. This affects the individual mechanical loading and therefore grip of the tires.
Removing weight from the car reduces the work the tire must do, and improves grip. Balancing the weight evenly in the car provides an even distribution for balanced response to dynamic changes. Intentionally biasing the weight distribution to a specific side or quarter of the car might be advantageous for the net results of grip under dynamic conditions. (You might want to shift weight to the right rear of the car at a track with a lot of high speed right turns to reduce the load of the left front tire, and increase the load of the right rear tire for more balanced grip during cornering).
Static weight distribution can be changed by physically moving objects within the car (relocating the battery, removing items from the car, etc.). It can also be changed by altering the ride height of individual corners of the car. Lifting a corner alters the CG location and in effect, increases weight distributed to the opposite coner. This is done primarily through coil-over shock & spring setups and by spacers.

Relocating the Center of Gravity
Relocating the CG to a more favorable position can also reduce weight transfer. Without getting into the engineering of it all, the location of the center of gravity acts as lever handle. We know from basic physics that a lever can be used to increase force and work. If the center of gravity is very high, there is essentially a long lever in the car. During braking, accelerating, or cornering, the G forces are amplified by this lever created between the CG point and the tire contact patches. The further apart they are, the greater leverage, and the greater the weight transfer.
With a given car, you can't change the CG location dramatically, but you do have some ability to affect the center of gravity enough to make major improvements to the car's handling performance. If you're willing to sacrifice some comfort, convenience, and looks, you can subtract and relocate weight to affect the front to rear and the side to side weight centers. You can also alter the CG height by lowering the car with lowering springs, lower sidewall tires, and to a smaller degree by adding removing, or moving weight in the car.
Once you have selected your car, there's nothing you're likely going to do to change the wheelbase or track width. You might increase track width a little with wider wheels though.

Weight Transfer and Suspension Components
We said that springs, shocks, etc. cannot change the amount of weight transfer. What they can change is the rate of the weight transfer, and the impact weight transfer has on the suspension geometry caused by dive (braking), squat (accelerating), and body roll (cornering).
The rate of weight transfer impacts the responsiveness of the car to driver inputs. The faster the weight transfer, the quicker the response. This allows the driver to have greater control of the car. However, a faster weight transfer requires greater skill of the driver. Smoothness and quicker reaction sensitivity to the tire traction are needed. It turns out that shocks have the largest impact on rate of weight transfer. The stiffer they are, the faster the tranfser.
The impact of weight transfer on suspension geometry has to do with maintaining as large and flat a tire contact patch as possible. When the body rolls, dives, or squats as a result of weight transfer, the geometric relationship of the suspension components to the body and the wheel changes the shape of the contact patch. For the unloaded tires, the patch size will be reduced. This effect must be minimized. Changes in shocks, springs, anti-roll bars, and wheel alignment are made to maximize the tire contact patches of all tires during the dynamic changes of weight transfer.
In the next articles which cover the major components, we'll define what those components do, and how they can be manipulated to control the effects of weight transfer and the changing tire contact patch size.

WHEN TO USE CAMBER KITS/DO I NEED A CAMBER KIT?

The real answer is its up to you. Do you want to handle better, reduce tire wear or have real control over your suspension?

ALIGNMENTS

Well you guys spend alot of money on your suspension parts right. Then you go right back to the OEM alignment which uh sucks. That alignment is not for performance. It is strickly to make tires last and make sure your car understeers. Both of those things don't make a car turn well. You will need a set or 2 of front camber bolts, and a rear camber kit to adjust camber.

The factory specs are as follows. [these are for the 8thgen Civics. What are the Fit's stock specs?]
Camber
Front
0 º 00 '±30 '
Rear
-1 º 30 '+1 º 05 '-0 º 45 '
Caster
Front
7 º 00 '±1 º
Total toe-in
Front
0±2 mm (0±0.08 in.)
Rear
2+2-1 mm (0.08+0.08-0.04 in.)

So why are these specs Crap? We want more oversteer without Murdering our tires right. A balanced less "pushy" car.
Well, If you look at the OEM spec's, Honda has setup these specs to pretty much allow for NO camber up front. And about -1 degree in the rear. Why? So your car understeers. This is so the car is safe for you to drive without the waggin the tail all over the place. This also does not allow for good turn in or a "fun" car to drive.

We need to change this. Why Camber does not eat tires. Ok so maybee it does but not nearly as bad as TOE, we will get to this. So the more -camber up front the car will handle better. TO a point anyway. And you need to balance out the rear’s camber to “match” to front to have a balance, slightly overteering FWD car is the "fast" way around a track.

TOE TOE eats TIRES!! Toe can help a cars handling. Too much toe and you eat tires and the car can wander on the highway. Too little and you are hindering the cars ability to turn.

Toe out on the front will tend to make the car turn in better and toe in on the nose will make the car understeer more. For the street I say 1/32 shouldn't effect tire wear enough for the gains.

For the rear, Toe out will increase the cars tendency to oversteer, where toe in will decrease it. More toe in to make it understeer more (less oversteer) More towards toe out to make it rotate more.
If you want to keep your tires ok and still turn well.

[These are suggestions for FG's (Civics), not our GD's (Fits)]
Camber Front = -1.5 to -1.75
Camber Rear = -1 to -1.25
Toe front = 1/32nd toe out I am now suggesting 0 Toe Most people won't be able to realize that the car has the toe, especially on the street.
Toe Rear = 0

EDIT by ERIC AKA bluroadster-toll booth operator- alignment specifications depend on the nature of driving. Driving on the twisties, one would want more - camber vice if one was driving on the highway all of the time where their style of driving would eat the inside of the tires.

A "race"/track day alignment is going to be even more wear but will handle better.

ALIGNMENT TERMS

Toe settings affect three major areas of performance: tire wear, straight-line stability and corner entry handling characteristics.

http://www.ozebiz.com.au/racetech/theory/image57.gif

To minimize tire wear and power loss, toe will be zero. Meaning both tires on the one end of the vechile are pointed ahead when the vechile is going straight. Too much toe in/out causes the tire to scrub, becuase the tire is always clocked away from the direction the car is going.Too much Toe out = Excessive wear on the inside shoulders
Too much Toe In = Excessive wear on the out side shoulders
“So if minimum tire wear and power loss are achieved with zero toe, why have any toe angles at all? The answer is that toe settings have a major impact on directional stability. The illustrations at right show the mechanisms involved. With the steering wheel centered, toe-in causes the wheels to tend to roll along paths that intersect each other. Under this condition, the wheels are at odds with each other, and no turn results.

When the wheel on one side of the car encounters a disturbance, that wheel is pulled rearward about its steering axis. This action also pulls the other wheel in the same steering direction. If it's a minor disturbance, the disturbed wheel will steer only a small amount, perhaps so that it's rolling straight ahead instead of toed-in slightly. But note that with this slight steering input, the rolling paths of the wheels still don't describe a turn. The wheels have absorbed the irregularity without significantly changing the direction of the vehicle. In this way, toe-in enhances straight-line stability.

Remember also that toe will change slightly from a static situation to a dynamic one. This is is most noticeable on a front-wheel-drive car or independently-suspended rear-drive car. When driving torque is applied to the wheels, they pull themselves forward and try to create toe-in. This is another reason why many front-drivers are set up with toe-out in the front

If the car is set up with toe-out, however, the front wheels are aligned so that slight disturbances cause the wheel pair to assume rolling directions that do describe a turn. Any minute steering angle beyond the perfectly centered position will cause the inner wheel to steer in a tighter turn radius than the outer wheel. Thus, the car will always be trying to enter a turn, rather than maintaining a straight line of travel. So it's clear that toe-out encourages the initiation of a turn, while toe-in discourages it.”

http://www.familycar.com/classroom/I...lign_t_toe.gif

(image from familycar.com)
Above is the wear pattern on a tire from a car that has excessive toe-in or toe-out.

http://www.ozebiz.com.au/racetech/theory/image60.gif

(TOP RIGHT) Positive camber: The bottoms of the wheels are closer together than the tops. (TOP LEFT) Negative camber: The tops of the wheels are closer together than the bottoms. (CENTER) When a suspension does not gain camber during deflection, this causes a severe positive camber condition when the car leans during cornering. This can cause funky handling. (BOTTOM) Fight the funk: A suspension that gains camber during deflection will compensate for body roll. Tuning dynamic camber angles is one of the black arts of suspension tuning.

“Camber is the angle of the wheel relative to vertical, as viewed from the front or the rear of the car. If the wheel leans in towards the chassis, it has negative camber; if it leans away from the car, it has positive camber. The cornering force that a tire can develop is highly dependent on its angle relative to the road surface, and so wheel camber has a major effect on the road holding of a car. It's interesting to note that a tire develops its maximum cornering force at a small negative camber angle, typically around neg. 1/2 degree.

To optimize a tire's performance in a corner, it's the job of the suspension designer to assume that the tire is always operating at a slightly negative camber angle. This can be a very difficult task, since, as the chassis rolls in a corner, the suspension must deflect vertically some distance. Since the wheel is connected to the chassis by several links which must rotate to allow for the wheel deflection, the wheel can be subject to large camber changes as the suspension moves up and down. For this reason, the more the wheel must deflect from its static position, the more difficult it is to maintain an ideal camber angle. Thus, the relatively large wheel travel and soft roll stiffness needed to provide a smooth ride in passenger cars presents a difficult design challenge, while the small wheel travel and high roll stiffness inherent in racing cars reduces the engineer's headaches.

It's important to draw the distinction between camber relative to the road, and camber relative to the chassis. To maintain the ideal camber relative to the road, the suspension must be designed so that wheel camber relative to the chassis becomes increasingly negative as the suspension deflects upward. (If you go tooo low with the si this is the opposite and you can lose camber as you compress the suspension) If the suspension were designed so as to maintain no camber change relative to the chassis, then body roll would induce positive camber of the wheel relative to the road. Thus, to negate the effect of body roll, the suspension must be designed so that it pulls in the top of the wheel (i.e., gains negative camber) as it is deflected upwards.

Since most suspensions are designed so that the camber varies as the wheel moves up and down relative to the chassis, the camber angle that we set when we align the car is not typically what is seen when the car is in a corner. Nevertheless, it's really the only reference we have to make camber adjustments. For competition, it's necessary to set the camber under the static condition, test the car, then alter the static setting in the direction that is indicated by the test results.

The best way to determine the proper camber for competition is to measure the temperature profile across the tire tread immediately after completing some hot laps. In general, it's desirable to have the inboard edge of the tire slightly hotter than the outboard edge. However, it's far more important to ensure that the tire is up to its proper operating temperature than it is to have an "ideal" temperature profile. Thus, it may be advantageous to run extra negative camber to work the tires up to temperature.

http://www.familycar.com/classroom/I...n_t_camber.gif(image from familycar.com)
Above is the wear pattern on a tire from a car that has too much negative camber.

“Caster is the angle to which the steering pivot axis is tilted forward or rearward from vertical, as viewed from the side. If the pivot axis is tilted backward (that is, the top pivot is positioned farther rearward than the bottom pivot), then the caster is positive; if it's tilted forward, then the caster is negative.

http://www.ozebiz.com.au/racetech/theory/image59.gif

Positive caster tends to straighten the wheel when the vehicle is traveling forward, and thus is used to enhance straight-line stability. The mechanism that causes this tendency is clearly illustrated by the castering front wheels of a shopping cart (above). The steering axis of a shopping cart wheel is set forward of where the wheel contacts the ground. As the cart is pushed forward, the steering axis pulls the wheel along, and since the wheel drags along the ground, it falls directly in line behind the steering axis. The force that causes the wheel to follow the steering axis is proportional to the distance between the steering axis and the wheel-to-ground contact patch-the greater the distance, the greater the force. This distance is referred to as "trail."

Due to many design considerations, it is desirable to have the steering axis of a car's wheel right at the wheel hub. If the steering axis were to be set vertical with this layout, the axis would be coincident with the tire contact patch. The trail would be zero, and no castering would be generated. The wheel would be essentially free to spin about the patch (actually, the tire itself generates a bit of a castering effect due to a phenomenon known as "pneumatic trail," but this effect is much smaller than that created by mechanical castering, so we'll ignore it here). Fortunately, it is possible to create castering by tilting the steering axis in the positive direction. With such an arrangement, the steering axis intersects the ground at a point in front of the tire contact patch, and thus the same effect as seen in the shopping cart casters is achieved.

The tilted steering axis has another important effect on suspension geometry. Since the wheel rotates about a tilted axis, the wheel gains camber as it is turned. This effect is best visualized by imagining the unrealistically extreme case where the steering axis would be horizontal-as the steering wheel is turned, the road wheel would simply change camber rather than direction. This effect causes the outside wheel in a turn to gain negative camber, while the inside wheel gains positive camber. These camber changes are generally favorable for cornering, although it is possible to overdo it.

Most cars are not particularly sensitive to caster settings. Nevertheless, it is important to ensure that the caster is the same on both sides of the car to avoid the tendency to pull to one side. While greater caster angles serve to improve straight-line stability, they also cause an increase in steering effort. Three to five degrees of positive caster is the typical range of settings, with lower angles being used on heavier vehicles to keep the steering effort reasonable.”

SWAY BARS

They connect both sides of the suspension together. When a car turns and weight is transfered to the outside wheel the anti-roll bar pushes on the inside wheel and compresses the spring, preventing body roll. How much the bar pushes on the inside wheel is determined by the size of the sway bar which means how much force it can push on the inside wheel. Preventing body roll, or making the stiffness of one end of the car stronger.

By changing the anti-roll bars is the basic handling balance of the car. Anti-roll bars are not just that. Preventing body roll is one job of them but their main job is to change Roll Couple Distribution. Roll couple is adjusted with spring and anti-roll bar rates. All that really is is the difference in stiffness (roll resistance) front to back.

The stiffer end of a vehicle will lose traction first. So if a car’s front suspension is stiffer that the rear, the roll couple distribution will produce understeer because the front end is handling more weight transfer. Chances are your car is heavily biased to the front. This is why the car understeers in most situations. By adding a larger rear bar you are adjusting that Roll Couple to be more to the back, reducing the cars amount of understeer. Do both bigger rear and smaller front or even no front bar and you get even more oversteer, how controllable is driver related, and what conditions you are driving in.

"Fun thing about anti-roll bars. in doing thier jobs of resisting body roll, they also increase the load on the outside tire. which, given the way tires make traction, means that there is a Net reduction in the total amount of traction that end of the car can make (the end with the stiffer anti-roll bar). So... in some cases, it may be advantagious to reduce the effectiveness of an antiroll bar. Such as on the front of a FWD car.

As weight is increased on a tire that tire generates a greater amount of traction, HOWEVER, that tires coefficient of friction decreases as weight is applied. Meaning traction increases at a decreasing rate as weight is applied, so there will be a point where the amount of traction gained is less then the amount of weight on the tire, and the tire slips.

This also means that a tire will gain traction at a slower rate as weight is applied then it will lose traction as weight is removed."

Meaning, weight transfer = an overall reduction in the amount of traction a car can make.... THE most traction your car will ever make is when it is sitting in a parking spot...think about it.

This sway bar discussion brings us into Motion Ratios, which will then go to
wheel rates etc. But we will discuss those items another time "

ANTI-ROLL BARS (SWAY BARS)
(from turnfast.com)

The primary function of anti-roll bars is to reduce body roll by adding to the roll resistance of the springs.
An anti-roll bar, also referred to as a stabilizer or sway bar, is a bar or tube which connects some part of the left and right sides of the suspension system. On independent suspension systems, the connection point is usually the lower control arm.
Most cars have a front anti-roll bar, and most sports cars are going to have both a front and rear bar. After market bars are going to be stiffer than the stock ones.

Roll Resistance
Anti-roll bars are used to reduce body roll during cornering. They add to the roll resistance of the suspension springs for a higher overall roll resistance Because the primary purpose of the spring is to maintain maximum contact with the road surface over imperfections, we must settle for the roll resistance provided, and it is rarely enough. The anti-roll bar adds to the roll resistance without resorting to an overly stiff spring. A properly selected anti-roll bar will reduce body roll in corners for improved cornering traction, but will not increase the harshness of the ride, or reduce the effectiveness of the tire to maintain good road surface contact.
So, how does limiting body roll improve handling? The suspension system geometry (the lengths and connecting points of its parts) of a street car is designed to keep the bottom of the tire parallel with the road for maximum contact patch. At rest, the car's suspension has a particular geometric relationship to the road surface. Body roll changes that relationship, and reduces the suspension's ability to keep the tire parallel to the road.
During body roll, the car body is no longer parallel with the road, and neither is the suspension geometry. Even though the suspension allows the wheel to be somewhat independent from the body, the high cornering forces, and resulting large body roll of a factory car, on the track take the suspension close to its limits where it affects the angle of the wheel.
Large amounts of body roll cause the wheels to tilt away from the corner which lifts the edges of the tire and reduces the contact patch size. While this can be compensated for by having the wheel purposely tilted inward to start (adding negative camber), there is a practical limit to this which is not enough in most cars to compensate entirely for the body roll. The anti-roll bar reduces the amount of body roll, and therefore helps to maintain as much of the contact patch as possible.
As with all good things, more is better only to a point. Because the anti-roll bar connects the left and right sides, this reduces the independence of independent suspension. Too stiff a bar, and you can cause too much loss in the ability of the left or the right wheel to independently respond to road surface imperfections. The purpose of suspension is to maintain maximum tire contact with the road. The purpose of independent suspension is to allow the left and right wheels to each seek that contact separately. The left wheel may need to be going down when the right needs to be going up. If they were tied together as with the old floating rear axles, one or both of the wheels is not achieving maximum contact. In fact, too stiff an anti-roll bar can actually cause an inside wheel to lift completely off the ground during hard cornering.
When cornering, the bar will twist with the outside end being pushed down, and the inside end being lifted (just like the body of the car). On the outside tire, this downward pressure helps increase tire traction. However, on the inside tire, the anti-roll bar is pushing up on the suspension reducing the downward force the spring is trying to place to keep the tire on road. If the anti-roll bar is too stiff, it will overpower the spring, prevent it from extending enough to keep the tire on the road, and the wheel will actually lift off the ground. This is not an optimum situation, but it is common in several racing classes. The cause is not so much poor engineering, but the limitations of the class rules that allow the engineer to compensate for it.

Roll Coupling
The anti-roll bar is also used to tune the roll coupling of the chassis. Roll coupling is the relationship of the roll resistance of the front of the car and the roll resistance of the rear.
The balance of the roll coupling, because of its effect on traction, has influence on whether the car has a tendency to understeer or oversteer. While this can be caused by several factors, the anti-roll bar (especially, an adjustable one), can be used to compensate.
As we mentioned, the anti-roll bar helps increase the mechanical downforce of the outside tire during cornering. This increases the traction of that tire, and that end of the car (front or rear). An increase in traction at that end, may leave the opposite end with too little traction. An imbalance of traction occurs, and one end of the car will lose traction before the other end. If the front tires lose traction before the rear tires, the car will understeer. If the rear tires lose traction before the front tires, the car will oversteer. Changing the anti-roll bar stiffness can adjust this out.

CHASSIS BRACING

"Chasses braces dont really alter the way the car handles much, What they do is remove the variable of chassis flex from the tuning equation, allowing the car to be more precicely tuned. And this is the important aspect from a compitition stand point. As being able to finely tune the chassis = better lap times. But in most cases your talking about a few tenths. So on a street car this really doesnt apply, as with out a timeing system your never going to notice if you were a tenth of a second faster in a given turn. DON"T WASTE YOUR MONEY.

The benifit of chassis braces on a street car, to me at least, are more psycological. See, chasses braces also make the car "Feel" more stable, solid. This in turn enspires more confidence in the cars capabilities. Which typically causes the driver to drive the car, conscious or unconsciously, harder. Where as the cars handling really hasnt changed. the driver is just driving differently. which explains why people claim that adding a strut tower bar or a lower X brace some how increased the amount of understeer the car has. When in reality, the car always understeered... the driver had probably just never had driven the car to that point to notice it.'

Any way. Point is for compitition chassis braces are important to allow you to get those last few tenths out of the car. For the street they instill more confidence in the cars capabilities, for better or for worse...

More:
https://www.fitfreak.net/forums/fit-...-extended.html

Good reads:
http://www.carbibles.com/
http://www.aa1car.com/
http://www.autozine.org/technical_sc...ech_index.html