Stage 1: the Alignment
WARNING!
This post is extremely long. I don't want to hear about wall of text comments or how you think it needs to be shorter. The fact of the matter is that alignment is extremely complex and its principles are the basic purpose of why the rest of the suspension is built and does its job. If you cannot, or don't want to understand alignment, you are setting yourself up to not understand suspension. You might then just call it a day, throw on a rear sway bar, and love how your car throttle steers so well and feels so much more docile until it decides to hump a telephone pole from which you cannot separate it until a wrecker comes by and tows your car to the junk yard.
95% of the suspension mods you will make will probably make your car "feel" better away from the limit, but also unwittingly lower the limit as well as create ugly handling characteristics at the limit that are undesirable. They may rarely be seen except on the autocross or the track, or when some kid decides to cut you off and you have to swerve, creating a maneuver that would have been doable by your stock car and now sets you up for a very catastrophic loss of control.
So if you don't feel like understanding the extremely complex topic of alignment, my suggestion is to just skip to "performance alignment on a stock suspension", then go to the next "stage 2 section" about firming up your chassis and drive line, then stop. Go no further, leave suspension bushings, springs, shocks and sways alone or you will set up a car that may at times feel better than stock, risks often being worse, and will definitely have lower limits. Until you understand the underlying principle of suspension is to keep a certain alignment of the tires and wheels through changing conditions, you will be doomed to buy more and more parts, slapping them on as band aids to make up for mistakes made earlier in the chain, snowballing into an expensive money pit of a car that leaves you hating the driving experience, and yourself.
Suspension, and most importantly alignment, is about the contact patch your tire has with the ground. The better the contact patch, and the more harmonized it is to the conditions your vehicle will be operating, the better traction you will have in those conditions and the better the car will handle. Period.
Another concept to keep in mind is that suspension changes, particularly ride height, will not only change static alignment, as will be discussed further in this and the ride height section below, but depending on what your alignment or ride height or ride stiffness is, your alignment can change depending on the degree of suspension compression as well. A prospective suspension modder should be familiar with not only what the alignment settings are (caster, camber and toe) before doing any mods, as well as what alignment changes certain mods might entail, but what the consequences on the alignment that your mods will have when you start driving around with the car which will differ based on your settings.
The other thing to keep in mind is the main factor that people dislike about STi's, particularly GR STi's is the understeer. If you don't want to bother with any hardware changes at all or spend money buying bushings, let alone the springs, sways and coilover gambit, the single biggest performance gain with your STi just like with power lies not in the hardware, but the programming. How many people who are ravishly satisfied with their stage 1 ECU reflashes get to say that their STi is still "bone stock" with just a hair of warranty related plausible deniability. The suspension is no different, perhaps the single greatest leap in performance as well as bang for your buck mod is a performance alignment on an otherwise stock setup. This helps to get around the negatives of a front McPherson strut setup which results in camber gain on compression, that is with braking for both tires or cornering on the outside tire which does most of the steering. Want to know more about why this is and how to set up your STi's alignment? Before telling you what to do as the end user, a refresher in alignment is needed, read on. With suspension, the integration of all the components in terms of their relative stiffness, along with the tires
and the alignment itself will be your tune.
Suspension is so dynamic that everything affects everything else more than with power. There are no right or wrong answers because a winning rally, autocross, DD or track setup are all different from each other, but it's not like there are multiple ways to get a certain set of bolt ons, like an intake, downpipe, pump and headers to work where the tune ties it all together. In suspension, the tune
is your choice of bolt ons. I cannot overemphasize the importance of knowing every step along the way in helping you the modder make it work, so let's start from the basics.
What is alignment?
Camber: Camber is the vertical angle of the tire with the ground.
Zero camber angle means that the tire is perpendicular, forming straight, vertical lines making perfect, 90 degree angles coming out of the ground like so : | |
Zero camber angle is actually good in straight line or low traction conditions. A drag race car going straight with a lot of power will benefit from zero camber because it will give the flattest contact patch going straight. Low speed, bad weather, mud, snow type vehicles also benefit from camber close to zero because the tires are flat. You're not going fast enough to roll one way or the other and so getting going in the muck is easier if your tires are flat on the slippery junk. Once you start turning hard and pushing weight on the outside though everything tilts outwards and compressing the suspension often leads to positive camber which lessens your contact patch.
Positive camber is bad, it looks like the tires angled outwards from the ground like this: \ /
You never want positive camber because it always robs you of contact patch. When going straight the inner surface of the tire doesn't see the road, the outer surface gets excessively worn, and going straight this is how it goes. Cornering usually gives you even more positive camber under most suspensions settings, so the awfulness of insufficient traction just increases. I only talk about it to illustrate that with McPherson strut suspension as the GR STi's have in the front, and GD's have front and rear, compression leads to increasingly positive camber and decreasing traction. The faster you turn, the less the contact patch, pure yuckiness. This is what you are working to avoid which is why I mention it. Everything you do in performance alignment is to minimize or avoid any kind of positive camber. Now that you know this is the enemy of traction, read on as to how to avoid it.
Negative camber is an angle of the tires tilting inward from each other like this: / \
Sadly many ghetto'ed out cars are lowered to extreme levels beyond what is useful because of changes in suspension geometry can produce excess negative camber. Yet just like wine and sun exposure which in excess are toxic, when used in moderation can introduce a world of positives where moderate, appropriate use seems to be associated with longer lifespan and less health problems.
Regardless of any suspension geometry factors, think about how the tires and their contact patches are affected when you turn. Most of the traction when you corner is not all four tires. Only a little traction derives gained from the inside tires. While it is good to maintain the largest contact patch through all four tires possible, most of your traction in a curve will arise from the outside tires where the weight will transfer as you make a turn. Furthermore, the corollary to this nugget is that most of your steering will be done by your oustide front tire, so you want to make sure that your front tires are optimized to have the best contact patch possible for the conditions they will be driven.
Let's look at it even further, think about the laws of inertia, when you turn the wheel the car's mass will want to keep ploughing straight in the direction you were going.
_ Direction of Curve and direction your front tires are steering
/ |
/
/
/
Net force on tires <---------- /\
|
|
|
Direction of travel
As you see, the mass of your motor, your driveline (see next section about driveline mods), your chassis, your wheels and tires, motor, suspension, seats, steering wheel, shifter, windshield, spoiler, lights, license plates and your ass as well as that of any passengers, anorexic, normal BMI or fat as well, wants to keep going straight. A stiff STi loaded with Viagra induced spunk with an attractive female Rally Navigator in your passenger seat is hotter than hell but it doesn't change the fact that all this mass wants to keep going forward and loads your outside tires which is perhaps one of the most important realizations in the physics of turning.
When you load a tire with force pushing to the oustide, it goes from this:
| | upper tire
wheel
| | lower tire
Top of Car
| |
wheel <-----cornering force
to this with lateral force of turning: \ \
Below Car
Now this is not accounting for suspension geometry changes. I am assuming that I am driving a suspension free car like a Lego with snap on rubber tires that just keep the same geometry because there is no upwards or downwards movement. Keep increasing the speed, and the lateral force will start to affect the lower, contact patch area will be warped when the car wants to keep going straight but the tires are trying to turn sideways. It's almost like the lower tire wants to get peeled off the wheel inwardsly (is that a word?).
The other concept that one must know about camber is dynamic camber change with cornering. In other words, suspensions rebound and compress with travel, bumps, acceleration, braking and cornering. When different types of suspension see compression, there can be changes in the alignment accordingly.
The Subaru GR generation, 2008-2014 Impreza WRX STi has McPherson struts in its front suspension, and double wishbone struts in the rear. These two types of suspension behave differently under cornering and any suspension modder needs to know the difference in order to know what suspension changes will give a benefit.
I will preface this description with a statement that the GD STi's had McPherson struts all around. This makes the car less capable for reasons that will become apparent, but the reason why the GD's were so much more intuitive is that the rear suspension lost traction more or less at the same rate as the front granting the driver the sensation of neutrality through a turn. McPherson struts actually gain camber (it becomes more positive) as you compress.
So a McPherson strut suspension might have zero camber in a straight line like this maximizing contact patch for straight line action assuming no compression
| | upper tire
wheel
| | lower tire
but as that strut gets compressed let's say you are turning right and loading the left side of the car, the oustide suspension will get compressed and start looking like this:
\Left Right\
Compressed/ outer loaded side Relaxed Inner side
\ \ upper tire \ \
wheel wheel
\ \ lower tire \ \
So wow, since McPherson strut suspension will sustain an increase in positive camber on compression, and a decrease, or more negative camber on decompression.
Wow, so you get a double whammy, first of all the tire will want to bend inwards, and secondly the tire is actually already tilted a bit outwardsly. So the outer edge of the tire will be compressed more into the tarmac than the middle, but the inner edge will be lifted, and this accentuates the inwards pushing furnished by the car already cornering and steering. The entire process robs you of traction on compression because assuming a zero camber angle at rest, the tilt of the tire will be wrong just with cornering, more so with compressing the oustide tires which do most of the steering and cornering. And this is where you see a lot of tire wear on Subarus, on the outer edge particularly on the older GD's which had McPherson struts at all four corners and the GR's more in the front.
This is why McPherson strut cars generally benefit from negative camber, the stiffer the suspension, the more negative camber needed to offeset the direction of the forces on the tire. Too much though will create tires that tilt inwardsly too much, wear the inner edges and straight line traction in bad weather or even braking in a straight line may suffer as the contact patch is not properly flat in a straight line.
The GR STi's have rear double wishbone suspension and because of this, you have camber
loss on compression. Therefore, as the shock & spring on that side get compressed, you have more and more negative camber, so that the same car turning right starting out with zero static camber like this |L R| would start to look in a way more congruent to offsetting the forces of hard cornering like this /L R/ if you are turning right. That left tire, instead of turning outwards and mashing the outer surface while lifting the inner one is more likely to stay nice and flat. So you have a more vertical tire when going straight, which is good, and one that leans into the curve while cornering, which is also good as it allows more of the tire surface to make a good contact patch wtih the asphalt.
This is why double wishbone is "better" because it helps maximize traction at all times, both straight line and in cornering.
But in the GR's, while the rear is double wishbone which enhances cornering traction in the rear, the front remains McPherson strut design which lowers available traction in the tires that turn. Therefore, while one might be able to apply more throttle assuming enough power is sent to the rear by the DCCD, the end effect is that the rear tires, which also have to deal with only about 40% of the car's weight, have way more traction. So the front will lose traction before the rear compounded by the fact that Imprezas are front heavy resulting in understeer. So while the GR's have faster track times because of this more "advanced" suspension setup that gives better cornering speeds from the rear's enhanced grip, in reality the GD's are easier and more fun to drive because the front and rear lose traction more evenly resulting in the sensation that you can give power to rotate the rear end. It's a more intuitive driving style in the older GD's because in GR's you might be able to give even more power assuming you are shuttling as much DCCD power to the rear, but it won't rotate you, but rather understeer you as you apply power speeding up and that is just a buzzkill.
Just take a look at the tires on any Subaru with McPherson struts, or the GR STi's front tires. The outside treat is worn and chewed while the inside tread looks fine. These tire profiles appear to show misalignment problems while in reality, the problem is in the dynamic alignment changes that need to be anticipated with a static camber setting. Decrease the camber to a more negative setting (remember more negative is "less" or a lower number) and you will have more contact patch, and therefore more traction when it counts. The amount of your ability to set negative camber will depend on your hardware. Stock suspension is good for about -1.4 to -1.5. Front camber adjust bushings will allow you to change that somewhat. Camber plates will give you an added stiffness in the suspension to take away even more play and allow you to sense the limit, as well as giving you large amounts of adjustment. How much you need is partly based on taste, but mostly dependent on suspension mods but realize if you stiffen the front suspension further, you will need to decrease (or add more negative camber) to make it work properly. Stock suspension can work in the maximum of its lowest range in the -1.4/-1.5 range. Upgraded springs like RCE blacks and/or mild sway upgrades will need -2.0 to -2.5 to work best. If you have coilovers with stiff springs and any swaybar work, ranges even lower than -2.5 degrees will likely be needed. Very sticky tires, particularly once you get in Hoosier territory levels well in excess of -3.0 up to -3.5 will be needed. Any more than that will do more harm than good, but again, this is a rough range, the "tuning" process is trial and error depending on your setup.
Also keep in mind that these numbers will require progressively stiff sidewalls and progressively more aggressive tires to work, so don't be using coilovers and all season tires at the autocross! Or if you are on stiff coilovers and threw on winter tires, then drive gently to avoid the tires from being overloaded, chewed up or peeled off the rim.
Toe
Toe is the direction in which the tires point relative the direction of the car. So zero toe in all four tires will have all four tires pointing straight forward like this as seen from above:
Left Right
Front
| |
| |
Rear
Toe-in is a condition where the tires will tilt inwards, and usually is used to decrease responsiveness. A quick and easy fix to decrease a car's rear end squirrelliness might be adding some toe in like so:
Left Right
Front
| |
/ \
Rear
Toe Out instead is when the tires point to the outside. If you want to make your car a bit more crisp, some platforms might allow you to add a little bit of toe out. The impreza is not one of them. Toe out on either the front, or especially the rear tires will result in excess squirrelliness and will make the car give out sooner than its normal limits. The car will feel nervous and uncontrollable. An STi or any Impreza should never have toe out, ever. For those curious, it looks like this with the rear tires toeing out as if each were wanting to steer outwards:
Left Right
Front
| |
\ /
Rear
The recommended alignment in all conditions is zero toe unless you want a slight abatement of very mild rear squirrelliness that you have no other way, or don't want to change any other suspension setting, even an easy one like a click on a coilover setting. Also, another word of advice is that if your car, particularly if brand new seems to be squirrelly, particularly under braking, is to check the alignment.
My car brand new looked like this
Left Right
Front
| |
/ /
Rear
It was toeing to 4-wheel steering with toe out on the right rear, and toe in on the left. It kept slightly pulling to the left and I had to keep adding a little right steering. Because I was always under slight steering, the car actually had barely perceptible torque steer on hard acceleration, which is another possible consequence of incorrect toe on a car that otherwise should not suffer from torque steer. This was off the lot!
Stealerships only get paid for warranty work if something is wrong, and the alignment tolerances can be significant. Mine were off by 0.20 and that was the "factory tolerance" so the stealership did not want to fix it. But truth be told, more than one alignment mechanic has told me that the biggest thing that is often off in a lot of cars is the toe going this way and that or being wrong. Zero toe is really the way to go as it also preserves tire life, but if you really need to stabilize your car for some high speed track runs, than maybe running 0.02 or 0.05 of toe in max might be of use.
Do keep in mind that just like camber, toe is also dynamic with suspension changes as well. Every time you change the camber on a wheel, its toe will change, and therefore must be reset. This is why cars that can automatically raise and lower themselves such as those on hydraulics must either be there from the factory (like the Porsche system in the GT-3's) that you can push a button and raise the car to clear slopes and angles, or be for static display only. Any time you change static ride height, you will change camber or toe as well and the toe must be re-set.
Further more the toe of the wheel also changes depending on which dynamic compression point it is located. Therefore the more the suspension compressed, the more change in the toe will occur per millimeter the suspension is compressed. That is why lowered cars are so squirrelly because at lower ride heights the toe change is so great that directional stability changes greatly from small suspension changes and the car feels unstable. What's even worse is that at very low ride heights, the rear GR suspension's toe changes will be very great, and in the opposite direction of the curve. If you turn right, your inside rear wheel will want to toe in, but your oustide rear will want to toe out, like this:
Left Right
Front
/ /
/ /
Rear
The effect of this low ride height is that you have terminal undesteer originating from the rear and the car feels like it handles like crap.
So kiddies, most of your work in suspension, now and forever should be at keeping static toe at zero, and doing things to minimize dynamic toe changes that create undesirable handling traits like lowering the car.
Caster
Let's take a break from the complex stuff and look at an alignment setting that is at least simpler on the surface to understand, if only because caster is not adjustable on a stock STi. There are ways to change it, both intentional and not intentional, and we'll get there. But to start, think Chopper motorcycle. Imagine you're back in the late 60's and you have a bike with the front wheel way in front and that long, forward sloping angle of your handlebars. That is a vehicle with a very large caster angle Indeed, caster is the steering angle, or the angle from vertical that you turn your wheels. A caster angle of zero might be found on say a bicycle where the handlebar axis is zero with the ground, you turn the handlebars and it directly shifts the front wheel like a rudder on a ship from exactly directly above. The more that angle is tilted backwards, the greater your positive caster angle.
If the car steers the wheels at 30 degrees, then your caster angle, looking from the left side of the car, looks like this:
Steering Mechanism is this
/ <- this is the angle that the steering linkage feeds into the tires
front ( ) rear.
That is a positive caster angle. So the steering doesn't happen from directly above, but the steering angle actually happens from just behind the wheels as that is where their axis points.
Theoretically, negative caster angle would be the wheels turned from in front of where the steering axis is, more of a backwards slopwing angle. Think the opposite of a chopper, with the handlebars being in front of the wheel and the motorcycle of bicycle wheel being where the pedals or the motor should be. This is physically impossible on a 2 wheel vehicle, and very undesirable in a 4 wheel vehicle, but for the purposes of teaching what caster angle is, here goes what it should look like as seen from the left side of the vehicle looking at the front wheels front (\)rear.
Now that you have an idea what caster is and looks like, read on to figure out what it does. In short, caster tends to cause:
-camber decrease in the outside tire when steering occurs
-weight jacking leading to compression of inside tires, particularly the front; this can enhance steering and make the car steer better but too much and the car gets squirrelly or even starts to understeer from excess front tire load.
-weight jacking leading to rotation of rear end and degrading cornering stability
-more centered "steady feeling" where the steering is stiffer and straight line stability enhanced; however too much and the steering wheel will start to communicate unwanted vibration and car may keep shaking for many seconds after hitting road bumps.
Increasing positive caster angle can be beneficial up to a point, but just like camber, not too much.
On stock STi's, the caster is in the high 6 territory, like 6.7 or 6.8 degrees. This is fine for almost all situations. I really cannot think where much more caster is desirable except maybe autocross because of the negatives that will come into play and make the car undriveable at higher speed. On the stock suspension setup it is not adjustable at all and this is a good thing.
I have encountered a situation of very high caster due to some miscalculations which led to a very, very squirrelly car that understeered and oversteered at the wrong times due to this weight jacking. However, it was a demon in autocross because if I felt I was taking a corner too fast I could just turn the wheel another quarter turn, and the camber loss (more negative camber) that turning the wheel creates would cause the front to grip and be able to take any corner. Probably the most powerful autocross mod might be less (therefore more negative) camber as well as more caster, but again, much more than 7 degrees will cause other problems, so watch out and go easy.
Lowering the car will increase caster angle, and if you are planning on doing a lot of other mods to the suspension, this is yet another reason not to lower your STi.
Camber plates almost always add about a degree or more of caster to levels of over 8 degrees. This may or may not be desirable, be ready to buy adjustable duroball bushings (more on that later) and turn them backwards to
lower your caster angle which is a solution that can work to offset excess caster from other mods.
Adjustable bushings in the rear LCA position, the aftermarket name being "duroball' can be purchased to allow for caster adjustment if you so desire more (or less) that your setup gives you. They can be turned to either add, or take away caster and are good for about 0.75 degrees up or down. Most of them except the metallic Whiteline bushing can only be pressed in once, like the Super Pro's, so you have to guess correctly and know more or less where you want it unless you feel like wasting a lot of money.
Caster also influences things like Scrub Radius and Kingpin Angle. Since the only place I really read about these rather than copying, paraphrasing or downright plagiarizing this article, I suggest the reader click on the below link and read this article.
The Ultimate Handling Guide Part 8: Understanding Your Caster, King Pin Inclination and Scrub
This concludes my alignment section. Remember that the suspension's job is to keep the best contact patch with the ground, and the contact patch will be dictated by the alignment. Failure to understand this highly complex element will mean failure to understand the suspension modding's end effects which will create undesirable, unpredictable unexpected and very frustrating handling traits. Set the front wheels at the most negative camber you can get equally on each side, zero out the toe on all four wheels, and you'll be well on your way to better handling.
Ready for more? Once you understand alignment we can actually talk about adding hardware and I will discuss driveline bushings and selected chassis bracing, coming soon in the next reserved post.