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Thread: The Suspension Setup Thread

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    Senior Member sr_rolla's Avatar
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    Default The Suspension Setup Thread


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    THIS THREAD APPLIES MAINLY TO SETUP OF A GRIP CAR BUT SOME THINGS DISCUSSED CAN APPLY TO DRIFT ALSO

    I've spent a bit of time looking through the different suspension related topics on ae86dc and Ive notice that nobody has accually posted much good info up on why things do what they do. Every body seems to put up posts along the lines of "use cut down falcon springs and suzuki seirra front shock and you'll be sweet" nothing about what real effect this has on the vehicle just that thats what you need to do. As such i thought it would be a good idea to start a thread to educate people on how and why suspension systems do what they do and hopefully save people some time and money in the process.

    so...

    1) a really common one i've noticed on here is that nobody seems to leave room for droop, a car need droop (the amount that the suspension hangs from static height) in the suspension system, whatever that system is, having zero droop will cause the car to be excessively bumpy and destroy shocks and other components. The wheels can only rise towards the vehicle but not fall away at all, so when the u go thru a dip of any sort, the whole car drops into it and gets hammered on the way out of said dip. In a racing/drifting/fast street circumstance, when you go through a corner, say a left, the right side of the the car should compress and the left should extend. With no droop, the right will still compress but the left will not and the car will hang wheels in the air. Whilst this may look cool, if the wheels are in the air the tyres cannot provide grip. A good amount of droop, no matter what the car or what the hieght is 2-3.5inches

    2) Lower is not always better, all cars, the aim should be to get the suspension arms/links/whatever parrallel with the ground to get the most balanced roll centers, or as close to it as possible. This is what RCA's correct on the front of ae's and ke's are for. If the arms are at to great an angle from parrallel (this goes for raising or lowering) the roll centers get out of whack and the car then suffers front bumpsteer and general poor handling characteristics.

    3)bumpsteer, This i caused when the LCA and the tie rod end run at different arcs in there travel and cause toe change, wheather by a + or - no. this causes stability issues under heavy braking mainly but all through the suspension range in some cases (see datsun 1600). With standard hieght cars, if any bumpsteer occurs it is usually out of the normal range of suspension travel and can't be felt. On a lowered car it is genrally fixed by raising or lowering the tie rod end mounting position or movung the rack mounts, theoreticly, it could be fixed by modifying the steering links so that they all run on the same radius. KE70's and AE86's VERY RARELY will get bump steer. What is normally felt on a ae or ke that is confused with bumpsteer is...

    4)Incorrect scrub radius, to picture this, run an imaginary line from the top of your front shock through your ball joint and onto the ground with the car at static height, front the front. Now on a KE/AE, most of the front tyre will be outside this line, what this causes is whenever u hit a bump, instead of just going over it, your wheel will be pushed back around the axis of your strut, which u feel as steering through your hand. Newer vehicles (with newer strut designs) do not experience this as much as AE/KE's due to a better scrub radius. I personally think that this may have something to do with the front end vibration several KE/AE's get at around 80kp/h. There are ways to fix this but they generally cause several other issues that are much harder to deal with, You now know what the feeling is, deal with it rolleyes.gif

    5) cars can be to stiff, jap drifters/circuit cars are way to stiff, they have access to circuits and even streets that are pool table smooth, we don't, run softer settings and go faster. Have a look at the gent on this site that has the valvoline sponsored ae86, his car has plenty of body roll, why? because it is needed to make the tyres work. If you don't run slicks, you don't need stupid spring rates (drifters may not apply here).

    6)negative camber, massive neg. will not neccessarally make your car handle better, if you don't have enough grip in your tyres to cause the tyre to roll onto its face in a corner then you have to much neg, simple as that (drifters may be different here) a road tyre cannot deal with massive neg and it will slide/understeer. Circuit style camber designed fro slick tyres will not work with a road tyre. It causes poor stability and poor braking due to a reduced contact patch (running 185's stretched over a 8 inch rim whilst looking cool, does not help this eather)

    7)caster, in laymans terms, this is camber that happens when you turn, both front wheels lean over during a turn due to the strut being pulled forward at the bottom or rearward at the top in a static position. On a street car this is more effective than negative camber in creating grip in a corner without regularly destroying tyres due to neg. However exccessive caster can cause high speed instability.

    8)track, a wider track does not neccesseraly mean a better handleing car, AE/KE's are blessed with a near on perfect wheelbase from factory (again drift may be different here) of length = 1.7xwidth. Massive track can make the car overly square and when done by using massive offset wheels, causes more problems with scrub radius as discussed before.

    Understeer/oversteer, in laymans terms, oversteer is when the tail kicks out, understeer is when the front slides and tends to go straight ahead instead of turning. generally, understeer scares the driver and oversteer scares the shit out of the passengers. In alot of cases over/understeer is caused by factory wheel alignment settings or wrong spring and swaybar settings.

    Rollcenters, as a car goes through a corner, it will lean, the inside of the car will extend and the outside will compress its supension. If you could picture an imaginary point about which the car rotates, this is the roll center. Rollcenters can be changed depending on suspension types but the best way to measure change is on a track. Making a sprinter have adjustable rollcenters is not overly difficult, we all know about front roll center adjusters and having several different thicknesses of rca will alow you to try different settings. The pic below shows how to work out front roll centers, this must be done on both sides to find the actual rollcenter where the lower lines intersect. As pictured, changing the angle of the strut or the track will effect the roll center but changing the angle at which the LCA sits will cause the most change. Now generally speaking, raising the roll center will cause more roll, lowering it will cause less. However, having no roll means that the cannot roll onto its tyres and will understeer, having it to high will cause the car to roll over to much and also cause understeer. A sweet spot must be found through testing of the car. There is no right or wrong here as different ride hieghts and driving styles will mean different sized RCA's.
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    For the rear it gets more complicated as the angle of the 4 link bars from front to rear has a bearing on the roll center as shown in the 1st pic below and much like the front, rear roll centers are dependant on driving style, horsepower levels, and ride height. the easiest way to make the rear system work properly is to make the 4 link bars equal length, parrallel with each other and the ground. This dials out all roll steer and as shown in the 2nd pic below, makes them no longer a factor in roll centers. Once this is done then a panard bar arrangment that can be moved up and down at both ends, or an adjustable watts linkage setup, can be used to adjust rear roll centers. The only other thing to remember when running a panard bar is that if the bar is not parallel with the ground (as in both end mounts are an even distance from the ground) the roll center will move left to right with suspension movement, it will also change to a different location between left and right corners, and cause left/right diff movement through suspension travel. Again there is no right or wrong here, a high hp car may run a higher roll center in the rear to force the cars weight onto the drive wheel in a corner and provide better drive where as a drifter might run a really low rear roll center so that the rears don't load up and cause eccesive grip or tyre wear.
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    Roll steer, i know there are other terms for this but its the term in using for this topic, roll steer is steering of the car through the rear wheels when the car leans through a turn, this is built into factory cars to induce understeer so grandma can get to the shops safely, not so good for us revheads. It is usually caused by having a setup that causes the diff to turn in relation to the car, in the case of sprinters, it is caused by having shorter upper arms in the rear 4link arrangement. Because the upper and lower arms have a different radius of movement when the suspension moves up and down, it causes the top mounts of the diff to be pulled foward on compression and pushed rearward (to a point) on extention, when the car is driving straight, this causes pinion angle change caused by the diff twisting, in a corner, 1 side is compressing and 1 side is extending so, its causes 1 side to be pulled foward and the other side to be pushed rearward. This is how the rear steering effect is caused. While most of this effect can be dialled out using swaybar/spring and shock settings, the only way to properly correct this is by running equal length 4 link bars, in doing this you effectivly lose your rear seats. It really depends on what you want more, rear passengers or proper handling.

    Pinion angle, this is the angle that the diff sits at front to rear. there is alot of argument over what the right pinion angle should be, for a traction setup, it should be a 0 degrees when the car is under heavy acceleration, that means that at rest, the diff should be angled slightly downward so that when the nose of the diff tries to rise under acceleration, the diff twists up to straight. The amount that the diff needs to be angled downward depends mainly on what bushes you are running, if they are spherical bearings (rose joints, pillow balls, rod end, heim joints etc) there will be littl or no movement so a lesser angle will be required as opposed to rubber or poly bushes.

    Ackerman Effect, Basically speaking, imagine u are on a go-kart, when you turn the wheel full lock the inner wheel turns more than the outer wheels, this is a good example of ackerman effect. Ackerman effect is the toe change that occurs when turning, every car has this designed into it from factory, without ackerman the car wouldn't turn very well at all, it can be effected by either the steering arm angles or moving the steering rack for/aft in the car. DO NOT fuck with ackerman effects, it can cause all sorts of troubles and is very hard to accurately test, don't touch, just try and keep it as close to stock as is humanly possible by making sure that you don't move the rack forward/backwards and you don't change the steering arms without checking that the ackerman is not effected by the change.

    Tyres, tyres need movement, fullstop, if you don't have any sidewall flex or tread deflection the tyres can't work properly, whilst a 185 stretched over an 8-9 inch rim looks cool, its wont provide proper grip. A near solid tyre with no sidewall flex will slide and is great for drift but on the curcuit it will not provide proper grip and on the street it is dangerous. Tyres are not just cheap, black round things for burnouts, they can provide a massive amount of information about what the car is doing and what may be wrong with a given setup. Next time your at a circuit meeting, talk to a race tyre technician, he will be able to explain what can be done with a depth indicator, temp gauge your eyes and hands. One of the few things of the top of my head that can be measured easily is camber setting effectivness. If you have access to 1 of those infared termometer guns, borrow it and go for a hard hills run or track day. Use the heat gun to measure the inside and outside temps of a given tyre, say right front. If the outside of the tyre is very hot and the inside is cool then more negative camber must be added, if the outside is cool and the inside hot then you have to much neg. simple as that. I will be adding more here soon.

    Aero aids, aerodynamic aids at road speed really are mostly a waste of time, however, having a front spoiler that is as low to the ground as is practically/legally possible will stop air getting under the car and aid high speed stability. Most rear wings are a waste of time, they do not genrally provide downforce unless they are higher than the roofline as if the are within the frontal area of the car the wing will pass over them (there are exceptions to the rule). However, if a rear wing is designed more like the TRD ducktail style rear wing, the flow of air off the rear of the car is interupted and the turbulence that normally happens at the edge of the bootlid, happens further back and causes the vehicle to be more stable.

    As was noted on a different forum, some of the pics in here have been taken from fred puhns how to make your car handle, credit where credits due and all that jazz.

    ill edit post when i think of more and have more time, thats it for now though.
    feel free to voice your opinions.

    constructive critisism and debate will be noted and or discussed, flaming will be ignored.
    Last edited by sr_rolla; 22nd December 2008 at 09:17 PM. Reason: pics

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    Senior Member sr_rolla's Avatar
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    (quote old thread ae71)

    i wouldn't disagree with any of that.

    good to see more about the proper side of things (grip hehe).

    any suggestions on maintaining front stroke with a massively low car, mainly the front?

    i have a few theories but want someone do discuss them with.

    also having really short rear sucks, i have 1" at most travel from normal hight to full extension, i need longer shocks, but they do keep the springs captive
    Last edited by sr_rolla; 22nd December 2008 at 07:20 PM. Reason: i can

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    Senior Member sr_rolla's Avatar
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    (quote konakid old thread)

    don't have the car 'massively low' perhaps?

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    (quote old thread ae71)

    well i want to maintain a low stance, if i manage to get a little more clearance on the exhaust i can go a tad lower on the front and a little more on the rear as well to balance it out as the front is fractionally lower. one thing that dose how ever prevent it from being any lower is the suspension stroke, there hardly any spring in the front.

    i also have no movement from the 10ish kg springs in the front. well put it this way there is a tight finger space between my tyre and guard and it doesn't touch even on rough roads. can't wait to go back to a 6kg spring

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    Senior Member sr_rolla's Avatar
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    you could modify your strut to use an insert with a similar overall length but with more exposed shaft, and getting a spring with a free length to suit that mounted further down the strut.

    sorry if that didnt make a whole lot of sense, if it doesnt let me know and i'll ge to it when ive slept, ive been up for 31hrs, soooo need sleep sleepy.gif , deal with my shitty spelling rolleyes.gif

    PS. i have got a few more things to add, will probably post on monday or tuesday night

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    Senior Member sr_rolla's Avatar
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    (quote old thread johnny_08)

    so how much caster would be recommended for a street 86 with suspension work? or would it just differ on the car and setup and/or personal choice? ive heard pple say run max castor for drift but for grip is it just trial and error?

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    Senior Member sr_rolla's Avatar
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    (quote old thread 741)

    For Grip you'd still want a bit of castor like +4 to +4.5 degrees. The effect the positive castor will give is a slight camber increase as you turn the steering further, which maintains the outer tyre's contact patch in the corner (as the outer tyre is loaded from the weight transfer). There is still alot more to it than that but thats the basics.

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    (quote old thread)

    my set up is

    -3.5 camber
    +4.5 castor
    1mm toe out each side

    fair low car

    drives very well i love it in the hills

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    on an AE86, max caster or near to it isnt that far off the mark, when i had my 86, i ran +4 degrees caster, any more than that with the springs and sway bars i had (read soft) and the car would become a little unstable at around 130, car felt like it wanted to turn at any moment, not nessecarily giving me any say in the matter rolleyes.gif

    basically what I'm trying to achieve with this thread helping people to work out what and why there car is doing what its doin without just using X brand springs at the rate my mate tommo recons is the right way and the shocks and suspension settings that fred on the forums said to use.

    I'm hoping that with imput from others on this site, i can help people sort out there own issues.

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    (quote old thread federal)

    one thing that will need to be taken into account when talling people to max out their castor is whether or not you have rose-jointed control arms....

    a good stable setup would be +3.5

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