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.

 

Stage 2: Chassis and Drivetrain

Good handling, just like good strength does not come from a stiff suspension, but a strong core. So once you're ready to start buying hardware or parts to bolt on, stay away from swaybars, and start replacing bushings instead! In my work as a healer I take care of servicemen who can spend all day lugging around 70% of the weight in battle gear that an Olympic weightlifter can only lift a couple times and still be able to win any hand-to-hand combat engagement with way too much body armor, guns and ammo strapped on them. They are thin, wiry thangs you would not think could kick the living daylights out of anything. But God save the big buff GNC muscle bound mutant who starts a fight with them from being thrown across the room bloodied and bruised. It's all in the core strength, and if you want to take your STi to the next level by upgrading hardware, don't start with curls, benchpress or squats for big arm & leg muscles, you need to start with Yoga and Pilates for the core.

Another way to think of upgrading your chassis and drivetrain is that stiffening your suspension will transmit the forces in other areas that are flabby and slop, so the responsiveness gain won't be as much. Your engine, transmission and differential are spinning bodies, and according to physics, work like a big gyroscope. Think of a 2 wheel vehicle that tends not to tip over once you reach more than nominal speeds. The reason why a bicycle or motorcyle on two wheels won't tip after you get going is the gyroscope effect. A body that has mass and starts moving in an angular, or cirular motion, such as a wheel will resist changing direction in proportion to the radius of turning, the mass, and velocity of the moving parts. So imagine what all the spinning weight your engine, gearbox, transmission, driveshaft and rear differential wants to do when you turn the wheel: it wants to keep going straight! This force will also deflect your car to the outside of the turn. Let's revisit an above posted set of vectors regarding alignment, only take into account a body within your car loosely connected to it (soft stock driveline mounts & bushings) moving straight heading at the speed you are trying to turn your car in the direction of travel.

Net force applied by drivetrain which is not actually part of the car
(hint, drivetrain wants to keep going straight and not changing direction, flopping sideways just like body roll, but unlike your car which is not moving, the fact that your drivetrain is turning transmits *more* force against your turning than if it were just a still body)

/ \
| _ Direction your front tires are steering
| / |
| /
| /
/
Net force on tires <---------- /\
(amplified by drivetrain |
wanting to go straight, making |
more work for your tires |
Direction of travel

Your drivetrain wants to keep pushing forward, and when you turn your wheel and your car rolls to the outside, this same driveline wants to flex forwards, and laterally on its softer stock mounts that are good at isolating NVH. OK, well the stock STi mounts are still better than most cars in terms of durometer, or stiffness of the rubber, hence the STi's more raw and solid feel compared to most stock cars. This feel can be improved for an even better cornering experience, so that when you turn the wheel you don't have an equal and opposite reaction against your steering force by the drive train thanks to a full driveline bushing bolt down. One minor player in the battle against understeer and mushy turn-in gets eliminated because now the drivetrain instead of flopping will be more directly bolted to your car and respond quicker. You also get a much better sensibility of the gas pedal. Ever wish you could be just as fast as traction control in feathering the throttle to where it needs to be but felt you could not keep up fast enough in most factory cars? This slop is why, and the sensitivity gained will help you control your car better by feeling what the driveline is doing. Given that everything is more stable, the car becomes more predictable and stable at the limit, when changing throttle input, or in high speed cornering as it is one less uncertainty to upset is balance. This feeling is further enhanced with chassis bracing (more on that later), suspension bushings (also more on that later) and a carbon fiber driveshaft which also serves to dampen away the sudden and undesirable behavior of upgraded clutches.

These higher durometer driveline bushings also are more durable, one of the few aftermarket modifications to a car that is actually lower maintenance and longer lasting, which is useful even in relatively stock-like STi's that are driven hard on track or autocross where this stuff can break, but in higher powered cars with extra shear forces transmitted to the driveline. Both of these situations (sometimes together if you're tracking a modded STi) beg for better driveline bushings avoid the drivetrain breaking its anchoring points and physically bashing itself into a mechanical failure against other pieces of your car.

You definitely feel a handling difference; the front mounts and bushings increase responsiveness and feel of the gas pedal as well as quell understeer. The rear related upgrades, particularly in the subframe, help significantly with the squirrelliness and snap oversteer that arise from hard braking at high speed. Both will make the car feel significantly more planted at all speeds. It's not quite enough to give you that BMW or Porsche feel of refined, steadfast stability, but for the amount of money and increased durability, it's a nice upgrade that you can set and forget without any other consequences down the line save for some extra noise.


I am providing a list of possible upgrade points as below. This is by no means comprehensive as every company has its own set and these may change with the passage of time:

1. Left and Right Engine Mounts where the motor attaches to the chassis. This increases responsiveness and tames understeer quite a bit
2. Pitch Stop which secures the motor from up and down movement. Stock is made of plastic and prone to breaking in higher stress environments; cuts down on engine movement quite a bit, adds slight NVH but not much.
3. Transmission Mount which can also cut down on understeer and increase steering responsiveness, but also improve shifting feel and action.
4. Gearbox Cross Member Isolator mount
5. Shift Linkage bushings make the car seem like a RWD with the shifter directly turning gears like a RWD pickup or true sports car
6. Front and Rear Shifter bushings also help shifter feel and bolt down transmission slightly; downside with these is that you cannot hold the shifter for long periods of time as all the vibration is transmitted now and staying in your hand will transmit these vibrations back to transmission and possibly cause damage.
7. Rear Subframe Inserts help keep the rear subframe that holds the driveline and suspension better anchored to the chassis for better throttle sensibility. Also decreases snap oversteer at high speeds as the stock STi does not feel terribly anchored at higher speeds and makes its economy car roots hard to forget considering its performance potential.
8. Whiteline rear differential rear mount bushing and/or inserts help give more throttle control. Please be aware that if you apply throttle and you feel a higher pitch not quite clunking, but slightly harmonic clinging sound from the rear, your differential bushings are probably worn and in need of replacement.

The possible downside is that second gear whine below 3000rpm in a stock STi now will pretty much be present more often, definitely through the first 3-4 gears, particularly at speeds under 40-45mph. You may also feel more engine vibrations, more so if you have forged pistons. The stiffer your bushings and mounts, the more prominent this Noise, Vibration and Harshness whine will be, especially if done in unison. I would like to mention that the engine, transmission mount selections probably account for a majority of the NVH, with shifter bushings, subframe bushings or inserts and rear differential bushings or inserts adding an extra bit of whine on top of that. How loud it becomes and how much it bothers you is entirely subject to personal taste.

You can look at my post reviewing my Milltek cat back exhaust and watch the videos of me driving around in side roads, on and off ramps and commercial areas as well as residential neighborhoods over a wide range of speeds likely to be experienced. There is whine, mostly under 40mph. Notice the exhaust sounds prominent, the Milltek in the video sounds louder than what it really is because of this driveline whine that is audible pretty well. Still a speaker cannot capture it fully, but the video, along with speech and other background noises gives the listener a good idea as to the overall loudness of a fully Super Pro & Whiteline bushing'ed driveline with Group N motor and transmission mounts present on my car:

http://www.iwsti.com/forums/gr-exha...7587-milltek-exhaust-subaru-cat-back-review-killer-b-elh-dom-1-5-catted-dp.html


The first line of equipment that actually meets OEM like specs but has higher durometer rubber is the group N series of mounts and bushings. The entire set (including suspension bushings which will be discussed later) can be bought for about 750 dollars as of early 2015 from Rallispec though is available from many distributors. These are OEM like rubber of higher durometer (stiffness) that work just like the factory set. One can go even stiffer with a lot of the other bushings but the most important NVH locations are the engine and transmission mounts. So it is indeed possible to get Group N everything, or go stiffer with urethane but upgrade the engine and transmission mounts to the stiffer rubber Group N's which give you 90% of the stiffness, but much less NVH.

Other motor and transmission mounts that are stiffer include the Perrin, Cusco and Beatrush brands, which get stiffer and introduce increasing NVH in that order. Beware the Beatrush mounts, they are quite loud. They do add a little extra stiffness but the perceived noise is considerable. The Perrin mounts are wonderful and barely harsher than the Group N but give a little more, but they are also astronomically expensive costing 600 dollars for the motor and transmission mounts alone.

As far as the other driveline bushings the issues with binding and lubrication are not present because these points see very little to no movement unlike the suspension, so long lasting lubricant selection and/or periodic maintenance for urethane parts is not really necessary.

This is also an area to pay attention with regards to SCCA regulations because some rules allow stiffer mounts but the places that screw in have to remain OEM like and cannot be metallic in certain places; other rules are stricter. So if planning to qualify for a certain class, always check with your governing or sanctioning body's updated rule book before buying and installing parts!

The rest of the driveline past the engine and transmission mounts can be found through a variety of distributors. The most discussed and generally highest quality tend to be Whiteline and Super Pro. One could make a case for either. Supposedly the durometer for Super Pro is more consistent from bushing to bushing in proportion to the OEM specs and proportion because they make them in the same place instead of Whiteline subcontracting to 6 different countries with different manufacturing processes that vary. What I mean is that say your rear differential bushings have a durometer of X and the shifter bushings have a durometer of 0.8x or they are 20% less stiff. Super Pro bushings supposedly will keep that proportion. This is more important in suspension to help preserve handling traits and dynamic suspension geometry and not introduce unexpected, unpredictable changes.

With the driveline it is less important but be aware that if you start stiffening up some things, but not all things at once, you don't get the full benefit. Basically that vibration will find its way to the softest place and if there are places that are not upgraded, the softer areas will get more shaking and tend to wear out and fail sooner. Some may have argued against this, it is difficult to prove or disprove who is right but if you're going to do this, you might as well do it all to enjoy the greatest possible benefit. It's one of those mods that make things more durable or better than OEM in all respects, even longevity, and makes the car more responsive, refined, stable as well as increases driver feedback providing for a better "seat of the pants" experience.

Another area where the OEM STi is not satisfying is the steering feel, and similar improvements can be had by upgrading the steering system as well as applying some chassis bracing in the right places. Driving around the factory stock STi as with most cars there is a certain vageueness to the steering in that slight side to side movements of the steering wheel will not translate into any control input. This is mostly because of the steering bushing slop as well as some slight chassis play which is easy to resolve with some bushings and bracing. The GR STi chassis is somewhat rigid thanks to factory bracing but the solid feel can be further improved to levels approaching or beating a german car through a thorough bushing and bracing upgrade; this is one of those areas, particularly in the front, particularly below the motor. Other areas of the chassis that tend to flex under cornering are further back but are less important and only noticeable in upgrade if running a very upgraded suspension and very sticky, upgraded tires such as ovesized slicks on the track where all the extra stiffness everywhere else adds to higher cornering speeds that will start to flex the chassis more.

The upgrades I have done are as follows:

A) Front Lower Arm Bar Type II bracing which helps steering feel enormously and curbs some understeer, if you're down doing steering bushings this is an inexpensive and effective place to brace.
B) Super Pro Steering Rack Bushings remove that play when you are turning the wheel.
C) Cusco Steering Mechanism Bracing will bolt the steering mechanism even more tightly to your chassis and eliminate some play as well.
D) The 2015 Subaru STi OEM 13:1 steering rack is one of my favorite mods as the car becomes amazingly responsive and capable of turning with small inputs of the wheel. The car feels like it shed 400 pounds from this upgrade though it tends to work better if everything else is already made stiffer to begin with as otherwise the faster steering will just slop everything else that much quicker. It is useful in track and autocross because you can countersteer more quickly if the tail is starting to turn on you, and again this ability is greatly enhanced when your car has all the other stiffening upgrades in terms of bushings.

Yes the 2015 rack works on GR's without DCCD or VSC problems, the system has some tolerances in the factory that will allow this part to work. More importantly, rememeber that the JDM STi's have the same DCCD and VSC as well as the 13:1 rack, so the factory system has some variance in the steering ratio built in. Make a long story short, this mod is a direct bolt on that works. You will have to take apart a lot of stuff in the front and likely need an alignment afterwards. Beware your tires being at crazy angles, you might have to DIY and eyeball some alignment before taking it in because the misalignment you can create with this mod is bad enough to chew up your nice tires in the distance it takes you to drive the car to your favorite local alignment place that is performance/modder friendly.

E) Group N Transmission cooler is something that makes your power steering mechanism, located next to the turbo, not overheat, not squeak or rattle and last longer, particularly if you are tracking or autocrossing the car.

F) A stronger transmission & power steering fluid like the Motul will also be helpful in steering feel, eliminating some hydraulic slop as well

Past this point I only recommend if you are doing track days on coilovers and slicks, otherwise these further chassis bracings won't do that much extra. They do make a difference, but it's so slight that unless you are running coilovers and full suspension bushings you'd be hard pressed to tell the difference.

E) Front crossmember power brace is a stiffer part that replaces an OEM piece. Not really necessary but if you have motor mods and the front strut tower brace won't fit, it may do a little.
F) Rear lower power brace and rear side member power brace stiffen up the chassis a bit. You can also do the front strut tower and rear tower braces but these add less. If you do the lower chassis bracing the strut tower brace adds little extra, and if you have things like an AOS, aftermarket fuel rail/regulator kit or larger intercooler, the front strut tower brace is unlikely to fit.
G) The GT Spec fender braces help a bit as well on the sides replacing the much smaller OEM ones, helping with turn in and lowering understeer slightly.

So there you have it, the secret to a sharp, responsive car is not stiffer springs or sways, but starts with a stiffer driveline and chassis. This mod set is fairly easy, still won't void any warranties (for the most part) and requires no special pre-planning or suspension tuning. It takes out a huge amount of slop and helps you make the most of your stock suspension. This stiffening also prepares you for things like better dampers, coilovers, track use. You'll be able to feel what the car is doing, and with these steering, chassis and driveline upgrades you can start to approach what the german cars, like BMW's and Porsches, feel like for a tiny fraction of the cost in exchange for some, but if carefully chosen, not too much NVH.

So when you want something more past a performance alignment and you're looking to upgrade your swaybars and are asking on this forum where to start modding leave your suspension alone. Do the full driveline bolt down, it's not that expensive, you may be happy stopping here like so many people with just stage 2. Even if you have extensive suspension mods planned, by starting with the chassis, steering and driveline you have just laid the foundation for a more successful jump to more suspension mods. These bushings and bracings will make your car feel so much more solid, stable yet responsive and crisp on their own and help you make the most of any possible suspension setup you might want in the future by taking your chassis and driveline to the next level.

I will finish by saying that these mods alone made my STi feel more responsive than a Porsche 911. Watch the video, if you stay away from really stiff motor and transmission mounts the NVH is very liveable and if you already have an STi you won't mind the extra little bit of noise, but will love the invigorating, seat of the pants feel these upgrades can bring.

 

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3. Transmission Mount which can also cut down on understeer and increase steering responsiveness, but also improve shifting feel and action.

While this is a good upgrade it really isn't going to do anything perceivable in the understeer department. If you want the transmission to move slightly less this along with a pitchstop, engine mounts and gear box mount bushings is a great mod, but if you want less understeer you'll be pretty disappointed as it has basically nothing to do with how neutral the car is. If you want less understeer get a stiffer rear bar or some coilovers with stiff rear springs or both.

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5. Shift Linkage bushings make the car seem like a RWD with the shifter directly turning gears like a RWD pickup or true sports car

In my opinion a shift linkage bushing upgrade doesn't make the shifter feel anything like a traditional shifter. It just makes it a better linkage shifter. Whether a car is RWD or AWD also has nothing to do with whether or not it uses a linkage shifter. A Porsche 911 along with many mid engine super cars are "true sports cars" that are RWD and use linkage shifters just like an STi does.

Thanks,
Geoff

 

Reserved for Stage 3: Springs and Sways, hardware part 1

 

Reserved for Stage 4: Suspension Bushings

 

Reserved for Stage 5: Dampers and Ride Height

 

Reserved for Putting it All Together

 

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Awesome. I await the next installments!

 

I am now ready to qualify as the least fun statement ever made on iwsti: once you've mastered your Subaru's handling potential as measured by the occurrence that any other driver you consider very skilled cannot obtain a time that is significantly faster than yours, then you can mod. Sad but true. Come back after a few track days, and if you come home thinking you need to fix a handling trait from the stock car with some mods, only come back to this essay once you start getting faster than other drivers.

This reminds me about a great discussion I was having with a fellow track-rat with a 997 GT2. There was another guy going through his ridiculous mod-list on his Hyundai Genesis - everything from an (ugly, if you ask me) aftermarket front bumper to his BOV choice. GT2 guy asks - is there another driver that can post a faster time than you can in your stock car? If so, you haven't reached the absolute limit potential of your car. If you haven't reached the limit "wall" of your car yet, then why modify it?

It's a very enlightening argument (which most of us very likely don't follow).

I love everything about this thread, looking forward to it.

 

is there another driver that can post a faster time than you can in your stock car? If so, you haven't reached the absolute limit potential of your car. If you haven't reached the limit "wall" of your car yet, then why modify it?

It's a very enlightening argument (which most of us very likely don't follow).

I love everything about this thread, looking forward to it.

So only the fastest driver on the track gets to mod eh?

Silly arguments.


PS: I missed anything about "How To Modify Your GR STi Suspension"

 

Sub'd. Excited to read whats next

 

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Thanks Toivonen, I've always enjoyed your real world comments and incite, subscribed

 

Subscribed!

 

I would love enough cash and time on a track to become an elite driver. Just not in the cards right now. Never the less having had jobs driving for a living I have a bit of experience behind the wheel. I am aware of the performance mods on my car. Every change I have made with specific desired affect. From a decent alignment to better tires. A lot of my research I did here when I make plans for changes.

I imagine lots of stis don't see much if any track time that have crazy mods. I am hoping to get to some events this year. Doesn't change my desire to make my car perform better. Or that I wont notice or be able to utilize any mods.

I can appreciate that there is a difference between a race car and dd. But our cars live in both worlds. That is why we got them. There is lots of info for both worlds here even some stance guys.

Each of these topics could be its own thread that could collect discussions. Be it parts, purpose price, procedure. Reading the experiences of not just race car drivers but guys who put their family and friends in their cars. And the guys that slam them and put in stereos. I like stereos. The engine forums have sticky's for everything under the hood. The discussion of the application of parts what helped me make my plan. To buy parts for a purpose whatever that may be.

I look forward to studying all this anyway and hopefully be able to help some others.

 

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sub'd. I hate these long posts, I tend to just skim through them, but I enjoy your contribution and there will be some great info here for future reference:tup:

 

Basically as I have time I will put in further info but I will take each step in succession because knowing more about each step in my experience was necessary to make the next step work. I will also go into great detail to show that a lot of common mods such as swaybars will actually lower your car's limit and it will be slower (though it will feel better until it will more easily fall apart at the limit) or without understanding the alignment needed to make it work will provide marginal benefit while the car actually feels worse.

And the biggest thing people hate, terminal understeer as well as unpredictable oversteer, are much better fixed with HP driver education.

Lastly becoming an HP driver has actually made me be able to enjoy driving in all situations, and enjoy driving more cars across a broader range of conditions. It also makes you a lot safer. It doesn't have to be that expensive. OK 15 track days and 10 autocrosses a year will get pricey on tires, brakes, oil changes etc. But 1-2 track days and 2-3 autocrosses per year will already teach a driver a huge amount.

The next section (which I am still working on it) is alignment. It is the most complex. It is going to be a very, very very LOOOOOOOOOOOONg post. But if one does not understand alignment very well, and you rush into bushings, springs and sways, you will fail. I guarantee that your lowered car with the sways you think will make it lots of fun and those fancy coilovers will have a hard time making it satisfactorily around curves. And I can tell you this with a high degree of certainty because it happened to me, and I thought I knew what I was talking about!

 

In for reads

 

I would emphasize technique over mods because technique will allow you to make the most of the mods.

Also most mods will actually lower your lateral G's. Swaybars seem popular but 99% of the swaybar setups will actually lead the car to giving up traction sooner than stock which lowers your cornering speeds. It's a cheap and easy fix to make the car more responsive and feel more exotic than stock, but the cornering limits are actually harmed and this was my experience until I started looking a bit farther into it.

If one does not have the attention span to read these long posts, then one lacks the patience and attention span to mod suspension, period.

But at the crux of it all lies a good driver. Good driver with lots of HPDE in a Mazda 3 can pass bad drivers in their 911's on track day or bury them in Autocross. I've seen it countless times. Springs before sways, track day before mods etc.

 

I just started intermittent fasting to get rid of the love handles

 

We're way off topic, but i started it and i was going to add to my previous post that in climbing, getting stronger allows only small gains because for fit people, getting stronger means gaining muscle mass, which entails gaining weight. Like driving, technique gets you further. Also like driving, serious people work at all the limitations they can.

FYI: i eat fairly healthy. Diet is one of the things that could be a limiting factor that I can control

Back to your regularly scheduled channel

 

looking forward to reading more.