Mach V Dan's mega suspension guide
I realize there's already a sticky in this forum by SUBE555, but in reading it and seeing a lot of the questions here, I still think it might help to go into a little more depth about suspension parts. And, I must admit, I didn't see it BEFORE I wrote all this, so my post looks disturbingly similar in some ways. Some of this post is a little redundant with the SUBE555 one...perhaps later I'll go back and we can merge or combine 'em.
From reading these forums, it looks like Legacy owners may (as a group) be a little less familiar with aftermarket modifications ("mods") than, say, Subaru WRX owners, who seem to run straight to the local speed shop after leaving the dealer. Not that any of you aren't intelligent, but just that you weren't born with Sport Compact Car magazine in your crib. With that in mind, I plan to write some posts meant to spell out the basics of Legacy modifcations as I know it. This is the first of several planned mega-posts. :) I promise I'll read all the stickies first next time.
For those of you who ARE experienced car modders, this may be information you already know. But you never know, you might learn something. Or maybe you can point out my inaccuracies.
Okay, now to today's topic: Suspension Mods. My goal is to outline the major kinds of modifications you can make to the car's suspension, what they do, and why you might want to do them. I also intend to help guide you in your shopping for parts, and to mention some of the tradeoffs in "upgrading" your suspension.
Major categories of suspension stuff:
- Springs and shocks
- Frame braces
- Sway bars
- Wheels and tires
(Ah, you're saying, "Isn't there a wheels & tires forum?" Yes, but we'll get to that...)
Springs and shocks
The springs and shocks probably do the most to give a car its handling character. Stiff springs and shocks make for a firm ride. Soft ones give a more plush ride but with lower handling limits.
(Note: Technically they're not "shocks" on our cars, but "struts." I know there's a difference, but I'm just going to call them shocks because I'm too fixed in my ways to stop...)
The job of the spring is to hold the car off the wheels, and to allow the wheels to move to follow bumps or dips in the road. The shocks' job is to dampen the movement of the springs; without shocks, the car would continue to bounce along indefintely after a bump.
Springs determine the car's ride height, so changing to different springs can give a lowered ride height. Reduced ride height lowers the car's center of gravity some, which can increase cornering grip. It also reduces suspension travel, though, so the car may be less able to handle large bumps without bottoming out the suspension. Of course, there are the everyday issues of ground clearance to consider; stock cars don't scrape their chins on those concrete stopers in parking lots.
Ideally, springs and shocks should be matched. Lowering a car normally means going with a firmer spring (otherwise the car might bounce off the bump stops too often), and the shock will have to be able to dampen the higher-frequency motion of a higher spring rate. If the car starts out with aggressive dampening, though, the stock shocks may be able to cope with moderately lower/stiffer springs just fine. The stock Subaru WRX shocks seem to work pretty well with mild lowering springs. Older Mitsubishi Eclipses, on the other hand, handled badly if you paired stock shocks and stiffer springs, and tended to blow shock seals.
Judging from the firmness of the Legacy GT stock shocks, it should work pretty well with a slightly lower and stiffer spring, without changing out the shocks. (The Japanese-market "pink" STi springs seem to be working well, judging from posts here.) A better choice might be to get a matched set of springs and shocks, or to get some adjustable shocks so you could tune the dampening to your liking. So far, though, I don't know of any aftermarket Legacy shocks outside of Japan, so we'll have to wait until the US aftermarket catches up.
Pros of spring upgrades: Improved handling, appearance; affordable
Cons: Potentially worse ride comfort; Reduced utility from lowered ride height; possibly mis-matched spring/dampening rates.
Coil-overs are a combination spring/shock unit that are integrated and specially-matched to each other. They're sold as a unit and usually offer a threaded spring perch so you can vary the ride height. (This adjustment is not motorized or anything; you have to jack up the car and manually turn the threaded perch at each corner of the car. It takes some time.)
More sophisticated coil-overs offer adjustable dampening along with the adjustable ride height. Often this level of coil-over will be paired with "pillow ball" upper mounts with replace stock rubber mounts with solid metal and spherical bearings, which give more positive location of the upper part of the strut, and also allow alignment changes. This level of suspension is what true race cars use. It is infinitely flexible and adjustable, and can be set up different for different tracks and driving conditions. Low and stiff for flat, fast tracks, higher ride height and softer dampening for tracks with lots of bumps.
Tein even makes an electronic control unit that allows for dampening adjustments of some of their coil-overs at the push of a button from inside the car. This really appeals to the gadget freak in me.
Where shocks are normally just replaced after several years, coil-overs are usually designed to be rebuilt. Depending on the type and brand, this may need to be done every two or three years.
Although coil-overs are the pinnacle of aftermarket suspension tech, I do not recommend them to most of my customers. My experience is that most people really don't need the ride height adjustment; we have rarely changed the ride height on a car after the initial installation. And most people don't really mess with the dampening much, either. For the average customer, a simple spring change, or a set of fixed-height springs with a performance shock, will be adequate and vastly less expensive.
Which brings us to the biggest drawback of coil-overs, and that's the price. Even the least expensive coil-over with fixed dampening will cost around $1000, and the fancier ones are in the $1,500 to $3,000 range for the set. It's worth it to some, but for most customers that's a bigger price tag then they're ready for, and the features would be overkill.
For hard-core track use, though, there's nothing better. And if you have money to spare, coil-overs can give an unparalleled level of handling combined with good ride comfort.
Pros of coil-overs: Adjustability, outstanding performance
Cons: Huge price tag, feature overkill for many
This category includes anything that is meant to reinforce the structure of the car. Types of product available include the ubiquitous "strut bar," or "upper strut bar," which ties together the tops of the shock tower; lower braces, which tie together the underside of the car; and various other bits to be bolted on to stiffen up the car's unibody.
The goal of these parts is to make the car frame more rigid; a more rigid frame means the car's suspension will move it the direction it was designed to, without deflecting in other ways as the car chassis squirms under the load. The result is better and more accurate handling, or so the thinking goes.
Usually these parts are made of aluminum, although you can also find them in carbon fiber or titanium. They bolt on easily, and really can help to make the body of the car more rigid. The benefit is real enough that many factory performance cars sport them; the current Lancer Evolution and 350Z both come factory equipped with upper strut bars.
Since they don't weigh much, the parts have little to no penalty in terms of performance. On the other hand, the benefits are also modest. Compared to springs, shocks, wheels and tires, the incremental improvements in handling from frame reinforcements are relatively mild. Adding a full complement of reinforcements will usually be more noticeable than installing just one.
There can be a down side with the under-car bracing in terms of NVH (noise, vibration, and harshness). Some parts of the car are deliberately isolated using rubber to reduce NVH transmitted into the cabin. If you bolt these parts together, you gain rigidity, but lose that isolation. Forum member gtguy talks about this in his Cusco front lower brace review.
Pros of frame braces: Low weight, modest cost, modestly better handling
Cons: NVH trade-offs with some parts. Not huge bang-for-buck.
Technically these should be called "anti-sway bars" or "anti-roll bars," but everyone calls them sway bars.
The sway bar ties the motion of side of the suspension to the other. That is, if the left rear tire starts to go up, the torsional force of the sway bar will try to push the right tire up. Or, to look at it from the other direction, the force of the other tire NOT going up is going to push back on the left tire.
The really great thing about sway bars is that if you go over a bump with BOTH sides of the car, the sway bar doesn't do anything. It just goes along for the ride, pivoting equally with both wheels. In this way, a sway bar can reduce body roll without all the negative impact on ride comfort you'd get by just putting on stiffer springs.
Stiffer sway bars will reduce body roll, although they will also reduce ride comfort when the car goes over a bump with just one wheel. They can also tend to make the car less progressive at the limits of traction.
Some people like to stiffen up only one sway bar to change the handling balance of the car. Although this can be fine in some situations, I prefer to install matched sets of bars on many cars. The engineers at the aftermarket companies have worked hard on their paired bars, and often I have found superior balance on matched sets compared to only upgrading one bar.
Note that most cars are designed to "understeer" at the limit of adhesion, which means if you lift off the gas when the car slides, it will tuck back in to line. Letting off the gas whent there's trouble is instinct for most drivers.
If you change that balance toward "oversteer," (which aftermarket sway bars usually do) the car will have a greater tendency for the BACK of the car to come out when you lift off the gas. For the untrained driver, this can be scary or dangerous. Always get some at-the-limit driving experience with your car after installing new sway bars!
Pros of sway bar upgrades: Flatter cornering, increased grip
Cons: Some ride comfort reduction, potentially more scary oversteer behavior
As mentioned above, many parts of your car are held together with rubber mounts. These rubber mounts a nice and QUIET. But they also allow lots of movement between the parts involved, which can result in slop in the drivetrain and suspension. Replacing these parts with stiffer versions is a direct NVH tradeoff. You are trading increased vibration and harshness for some amount of greater control and directness. Whether this tradeoff is worth it depends on you.
There is a world of bushing replacements for the WRX, from tranny mounts to motor mounts to "pitch mounts" to strut tops. Some of these may be applicable to the Legacy, too.
Usually these would be the last step in building a sharp-handling car, although some of our customers do them just because they're relatively affordable by the piece.
Pros of stiffer bushings: More precise location of driveline and suspension, better handling, less wasted power.
Cons: NVH! Bang-for-buck not too great.
Wheels and tires
There's a whole other forum devoted to this, but I wanted to mention it here because of the signficance of your wheels and tires as a part of your suspension.
Wheels don't really DO anything; they just carry the tire. Other than reducing weight (which is always good), changing to different wheels won't really help your handling. If you are reading this, you probably already have 17" wheels, and going up a size or two to 18" or 19" will probably not give any gain in grip. Additional wheel WIDTH may allow for a WIDER tire, which may improve grip some, but the difference will not be huge.
But TIRES are probably the single biggest change you can make in the way your car handles. The difference in grip levels between all-season tires (which the car comes with), and high-performance dry-compound tires is really dramatic. And the difference between a performance street-compound tire and a track tire ("R-compound") is another leap. If you put R-compound tires on a car with stock suspension, and had all-seasons on a car with every other suspension modification, I guarantee the R-compound/stock suspension car would turn faster laps at the road course.
If you live where it gets snowy in the winter, get some dedicated snow tires and some nice dry performance tires. If you live where it never snows, get some good rain-worthy high-performance tires. Or get really crazy dedicated dry-weather high-performance tires (uh, my Evo still has the nearly-slick Toyo RA-1's on it), and just duck and cover when it starts to look like rain.
Pros of high-performance tires: Dramatic increases in performance
Cons: Expensive! Purpose-built tires not so good outside their element.
I hope this helped. If you have questions you think others might want to know, post them here. If you have questions that are only relevant to you, PM me. If you don't agree with me, please don't reply at all. Just kidding! ;)
Thanks for reading.
I was searching and saw this...bump.
great write up
Def awesome for any n00b and for most of us just for review and to keep us inline =)
Also should mention that suspention mods are a must if adding performance to the engine
good write up, can't believe it went un-noticed for 6 months. --- this should be merged with the other sticky to get all this good information in one place.
Hey, thanks. I had forgotten about this post, as well.
Bump for some good info!
why bump a "stuck" thread ;) hehe
If I was more awake, I guess I would have realized that....:redface:
helped me answer alot of questions!! +1
helped me too, thanks heaps.
Great info; how about a section on alignment
Thanks for a very well written and thought out post. You obviously put a lot of time into that.
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