Author Topic: Basic Suspenion Tech  (Read 4560 times)

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Offline Thundercat

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Basic Suspenion Tech
« on: May 19, 2009, 11:36:52 am »
For those who dont know the suspensio n facts as well as others maybe this info will be able help you understan d the facts of a suspensio n...

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 significa nt 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 suspensio n'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 automotiv e a compromis e 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 suspensio ns because camber constantl y changes as the suspensio n is compresse d and expanded. Generally speaking, any independe nt suspensio n will increase negative wheel camber as it compresse s, 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 suspensio n at a given amount of compressi on or expansion .

CASTER: Caster is the angle of inclinati on 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 direction al vehicle stability, camber gain during steering, and also plays a roll in anti-dive character istics 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 increment s 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 character istics. 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 direction al stability to suffer (and stability under braking to suffer greatly).

TOE CURVE: Just like camber, toe amount changes as the suspensio n undergoes movement. Suspensio n designers generally take full advantage of this and design the suspensio n to take on reduce toe amounts as the suspensio n compresse s, thus allowing the vehicle to remain direction ally stable during normal driving yet more eager to change direction under braking.

SET BACK: Measures the differenc e 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 perpendic ular 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 simplicit y 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 suspensio n or frame has been bent.

SAI (Steering Axis Inclinati on): 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 suspensio n 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 suspensio n). 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 perpendic ular to the ground (imagine a second line drawn verticall y though the center of the hub). The differenc e 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 suspensio n component, as this concept is centered around suspensio n 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 perpendic ular to the ground, I wasn't being perfectly accurate for most any independe nt suspensio n 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 differenc e 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 everythin g will be pivoting on at normal ride height.

SCRUB RADIUS: The differenc e between where the SAI line and the vertical wheel centerlin e 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 centerlin e. Scrub radius is important to both vehicle stability under braking and accelerat ion, 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 effective ly 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, maximizin g 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 enthusias t 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 determine s 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. PROGRESSI VE RATE COIL SPRINGS: A linear spring has a straight compressi on rating, meaning that for our earlier example it would take 300 lbs of force to compress the spring every inch throughou t it's total travel. Say the car weighs 300 lbs at one corner, well the spring at that corner would be compresse d one inch once installed . For each additiona l 300 lbs of pressure put on the spring, it would compress an aditional inch until it reaches minimum height. If the spring is termed progressi ve rate however, this rate changes as the spring is compresse d. Many springs are progressi ve rate because it allows the suspensio n to be softer initially (making ride quality better) but stiffenin g up as the amount the spring is compresse d increases . This allows you to make the spring fairly soft at smaller compressi on while making it stiff enough at bigger compressi on amounts to accuratel y control wheel & suspensio n movement when you are hauling ass. Progessiv e springs usually allow the car to ride & handle better if they are properly designed, but the added complexit y to designing and making them work properly also increases the possibili ty of screwing things up. For these reasons linear springs are often still used for our cars, but if you can find good progressi ve rate springs from a reputable manufactu rer 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 dissipate s 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 determine s the resistanc e to movement the shock will have, and adjustabl e shocks have adjustabl e sized orifices to offer a range of resistanc e 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 compresse s again and then jumps away once more. A spring will do this just the same, causing the suspensio n 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 importanc e of getting the shock stiffness right for your springs. The secondary job of the shock is to add some resistanc e to motion in the suspensio n, 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 performan ce.

ADJUSTABL E SHOCK ABSORBER: Adjustabl e 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 understan d 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 suspensio n can be compresse d (because it adds additiona l resistanc e to the whole system), you can imagine that making the shock stiffer will have the same overall effect on ride quality as stiffenin g the spring. There are two main types of adjustabl e shocks: those that adjust stiffness of the compressi on stroke only and those that adjust stiffness on both compressi on and rebound strokes. It's not important to go over the different types of desgins here, but know that most shocks either only adjust compressi on stiffness (called single-adjustable shocks) or they adjust both compressi on & rebound at the same time (called double-adjustable shocks). This means that there is no way to adjust the bias between compressi on & rebound stiffness on double-adjustables, which is of principle design concern to shock manufactu rers because it's so easy to get the bias wrong. There are indepentl y double-adjustable shocks which allow you to change this bias, but I wouldn't recommend them for the average enthusias t. You will probably just end up making the suspensio n damping worse than it was stock. Recommend ations here are usually to get the double adjustabl e shocks that control both compressi on & rebound (but not independe ntly), and that's probably the best idea for the average enthusias t.

COILOVER SUSPENSIO N: A coilover suspensio n 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 accuratel y control spring movement, plus it's usually the lightest. In our double wishbone suspensio n systems, the shock's only job is to control spring movement, so it makes sense that Honda equips all of their performan ce 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 exclusive ly the coilover setup on their current cars. Aftermark et spring manufactu rers like Ground Control simply one-up their design by adding height adjustabi lity to the system. This comes in the form of threaded shock bodies and adjustabl e spring perches, we generally refer to them as "sleeved springs". There are also shock manufactu rers like Koni who one-up Honda in the shock absorber departmen t by offering adjustabl e shocks, which are adjusted usually by a knob 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 adjustabl e in several different ways (height adjust, rebound adjust, compressi on 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 rebuildab le 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 garauntee d match between spring & shock are usually the stock units (which of course are not stiff enough and have no adjustabi lity). What I am getting at here is that just because you get springs from one manufactu rer and shocks from another does not mean that you won't have a kickass ride, it just means that there is more possiblit y of mismatchi ng one part to another. As we have pointed out many times, the simple Eibach Pro Kit & Koni adj. shocks combo seems to whoop ass on many other street setups without costing an arm and a leg (relativel y speaking).
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~CREW LEGIT~JJ AUTOWERKS
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Offline Thundercat

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Re: Basic Suspenion Tech
« Reply #1 on: May 19, 2009, 11:37:45 am »
How do sway bars work, and how can you use them to tune your carís suspensio n?
Most performan ce people know that stiffer rear sway bars reduce the understee ring tendencie s 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 understan ding of what goes on in your suspensio n when you take a corner. First, let's get an understan ding of what lateral weight transfer is, because this will help you understan d 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 centerlin es 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 determina te in how much weight is transferr ed laterally on a car for a given amount of steering input. This is something many people have a hard time swallowin g, but neverthel ess it is true. All the springs primarily do is determine how much the suspensio n 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 accomplis h it. Now we already know that limiting body roll can improve handling (depending on circumsta nces and suspensio n 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 selective ly increase spring rates only under cornering so that our straight line stability & tire to road contact is not compromis ed by really stiff springs? The sway bar is the answer.

Now it should be stated here what sway bars essential ly do, even though I know you may already know this. What a sway bar does is counterac t the action of body roll during cornering by transferr ing 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 transferr ing load from the inside tire to the outside, which has the visual effect of compressi ng the suspensio n on the inside of the turn and expanding the suspensio n on the outside of the turn (thus limiting body roll). This is good mainly because it smoothes the speed of weight transfer during quick transitio ns and also limits the camber change experienc ed at the corners of the car through suspensio n travel. And of course, using this concept one can dial in the amount of total loading on the outside tire by varying the effective ness 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 understan d 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 distribut ed 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 controlle d 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 understan d that increasin g tire loading adds to the total amount of traction available from it, but this relations hip is NOT linear. The more load on the tire, the more traction available, but the amount of traction gained diminishe s 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 increasin g the differenc e in load distribut ion. 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 ultimatel y 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 increasin g 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 explainin g how sway bar sizing (which directly reflects it's roll stiffness amount) cures an unbalance d car. If a car is understee ring, it's because the rear end has more total traction than the front. If you put a big sway bar on the rear suspensio n to limit the total amount of traction available there (by maximizin g the amount of load transfer to the outside wheel), you can dial it in to match the front suspensio n'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 suspensio n movement.

If i missed anything please add to it.
~CREW LEGIT~JJ AUTOWERKS
~IMPORTALLIANCE.ORG~All IN FAB~BISIMOTO~

Offline BLU CIVIC

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Re: Basic Suspenion Tech
« Reply #2 on: May 19, 2009, 04:21:40 pm »
i have an indepth suspensio n calculato r that i can add to this...i just need to figure out how to host an excel file
The name's Adrian


Offline Caged91ZC

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Re: Basic Suspenion Tech
« Reply #3 on: May 19, 2009, 04:33:20 pm »
applaud to u sir. that's quailty post!

dare sticky this

Offline Thundercat

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Re: Basic Suspenion Tech
« Reply #4 on: May 20, 2009, 04:39:51 pm »
thanks ....
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Offline Straightsix

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Re: Basic Suspenion Tech
« Reply #5 on: May 20, 2009, 04:43:57 pm »
I was going to sticky it last night, but only just now found the button to do it.

Offline S.Brewer

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Re: Basic Suspenion Tech
« Reply #6 on: May 20, 2009, 11:42:07 pm »
Great topic, i knew of most, but i really like the details. It helped me understan d that extra 2 steps. Thanks
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Re: Basic Suspenion Tech
« Reply #7 on: May 22, 2009, 03:45:50 pm »
awesome post and very informal

Offline sir_christopher

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Re: Basic Suspenion Tech
« Reply #8 on: August 08, 2009, 03:45:51 pm »
very nice!, now  i need to find suspensio n on a budget

Offline dudebuddy

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Re: Basic Suspenion Tech
« Reply #9 on: October 14, 2009, 11:38:36 am »
i feel like i just went through alignment school again.... good write up...this is must need to know info when doing alignment s!
you eventuall y sit back and look around to see that most of the pieces that are falling, are falling in place.

Offline nukefivesix

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Re: Basic Suspenion Tech
« Reply #10 on: January 15, 2010, 01:06:49 am »
i can add a couple things to this, since ive seen several efs with this problem-
BUMP STEER
Bump steer is the term for the tendency of a wheel to steer as it moves upwards into jounce. It is typically measured in degrees per metre or degrees per foot. basically, when you hit a bump, the car steers on it's own

Excessive bump steer increases tire wear and makes the vehicle more difficult to handle on rough roads.

i havent been an alignment tech for a couple years but iirc a common cause of this worn ball joints, and worn track rod bushings, basically the cause of this is poor suspensio n geometry

ive had this problem before, and its very bothersom e.. good write up @ op

usk.. the world has never seen such greatness ..       ..thanks for the sig busdriver j


 

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