RichP

Since the PSS's are on a 4 month backorder and I'm too cheap to splurge for the PSS9's I thought this might be a good compromise for ~$800

Larrytt

cough, cough . . . cheapskate . . . cough . . .

gtt

Eibachs were also on back-order till mid september at shox.com

TTschwing

Fully-Adjustable Coilover Suspension for the street? You sure you wanna do that?



Are you committed to buying an adjustable coil-over suspension for the car? Contrary to Audiworld opinion, an adjustable coil-over suspension on a street car is a poor idea and can hurt the handling of the car. Allow me to explain.

The whole purpose of a fully-adjustable coil-over suspension (FACOS - not an industry term) is, as expected, adjustability (do you know that you already have coilover suspension, stock?) However, with that adjustability is a LOT of setup requirements. If you don't setup the suspension properly, you are almost guaranteed to make your car handle worse than stock. It might ride stiffer, and look lower, but it won't handle better. See, the FACOS give you not only the ability to adjust ride height, but corner weights as well. If the corner weight is not set correctly then you end up with cross-weight all out of whack and the car's handling becomes unpredictable.

Think of corner weights this way: you take a four-legged stool with all legs the same length. When you sit on that chair, all four legs are touching the ground evenly, pushing down onto the ground evenly, if you will, and the chair doesn't rock. If you were to place scales under each leg you would find that with your weight perfectly balanced in the center of the chair all four scales would read equally. Lean one way or another and you'll find that the weight will be shifting from scale to scale but the chair will continue to be steady and not rock. The reason is because of one unique thing: the sum of the opposing corners will always equal each other. In other words, the LF plus the RR weight will always equal the RF plus the LR weight.

But, suppose you slightly trim one chair leg, say 1/16". Now, the chair is going to rock slightly, because more of the weight is being held by the opposing corner legs. In fact, if you're good at balancing, then 100% of the weight will only be on two legs, while the other two legs aren't even touching the ground. The LF+RR weight will be LESS than the RF+LR weight.

This is the idea behind corner weights on a car. FACOS is adjustable not just for ride height (different length springs will do the same thing); the goal is to adjust each spring independently so that the cross weights are identical. You'll still have more weight in the sum of the fronts versus the sum of the rears (and you can adjust that to a degree with spring rates), but when the sum of the cross weights are equal the car will handle the same left to right and will be MUCH more predictable.

If, for instance, you have too much weight LF/RR than RF/LR, the car will turn in nice and sharp to the right, but will understeer in transit through the corner, and probably during exit. To the left the car will lean over more, transfer a lot of weight during the turn in, and then probably oversteer through the corner. It won't be fun to drive either way, and you'll be scratching your head trying to figure out why it's an evil-handling car.

To set up a car properly with a FACOS, you:

- install your suspension and set the spring perches about where you figure you'll need them for ride height, and equal all around.

- put the car on the ground and test ride height. Ride height is set to either race prep rules (minimum ride height) or to the lowest you can for the conditions. Those "conditions" are either external limitations (don't want the exhaust or spoiler to drag the ground) or internal (wheel clearance or bump stops.) That ride height also has to be adjusted based by testing to determine that you have enough suspension travel and the suspension doesn't bottom out; if you bottom out the suspension you're making your "spring rate" go infinite and you've just wasted all your money on an adjustable suspension. Also, don't forget the ride height is adjustable front and rear, left and right.

- After the ride height is set then the car needs to be aligned to spec. That "spec" is either to the factory limits (which you will likely never be able to obtain with a lowered car) or to values based on track testing, tire pyrometer temperatures, tire pressure results, and driver feedback.

- Once the ride height and alignment is set, then the car needs to be placed on four independent scales. These scales will give you the corner weights that you need to know to set the suspension properly. The nifty versions of the scales are digital and radio-transmitted, and give you a display box you can take with you around the car while the car is on a lift on the scales and you adjust the suspension with another display that does the math for you (about $2000 minimum for ones like that). What you want to do is adjust each spring perch independently so that the sums of the cross-weights match. If a corner is low, you extend the spring perch (chair leg) to put more weight on that corner. Of course, that will then affect all 3 other corners, so you have to go around and around until you get the numbers you want.

Of course, this is all assuming that you're running the springs you want, because a different spring rate will cause front-to-rear weight transfer and change all those adjustments...

- once you've made all the corner weights perfect, you have to go back and check the ride height, because it's quite possible that all the corner weight adjustment has changed the ride height. If so, start all over again. Don't settle on "good enough"; the whole point of getting FACOS is to get it RIGHT, right?

Then, once it's all set, it's time to go to the race track. Start on the skidpad and check handling. Slight changes in alignment and ride height will help you here (with associated updates to corner weights), but if you need to change front-to-rear bias for better handling you have to change springs (but, of course, one of the big advantages to FACOS is that it uses standard springs - you get to pick-and-choose your spring rates for each end.) Change the springs, start from the top, Maestro! You can also tune the corner-weights for a particular race track, like Lime Rock which is all right turns save one; of course that will make it suck on the street where you're going to be hard-pressed to find only right-hand turns...

You asked if the springs can be installed for $200? Dude, you can't even properly align and setup the car with the springs INSTALLED for $200!!!

Whew! Have I gotten my point across?

I have a FACOS on my little Nissan race car, but I have a $1200 set of scales. We'll spend an entire day on initial suspension setup, and constantly twiddle with it at the track.

I would NEVER install FACOS on my street car. The ironic part is that any "tuner" worth his salt has gone through all the above with an adjustable suspension, tested it to perfection of spring rates, travel, and ride height and alignment, and then took those specs and developed a comparable off-the-shelf replacement spring to give you something probably DAMN close to what you're gonna end up with on a FACOS. It just makes no sense to have all that adjustability, ESPECIALLY considering that when you finally get it set up you'll likely NEVER change it! Because if you do, you've got to start all over from the top. Kinda silly to have that adjustability when it ain't ever gonna be adjusted...

Installing a fully-adjustable coil-over suspension on a car without properly setting it up is either posin' or pissin' in the wind. It may look nice in your sigline, but you're actually hurting the car's handling.

As an alternative, consider the costs of finding a top-notch set of adjustable shocks and aftermarket springs, and paying someone to swap out the springs twice a year like you would for snow tires. You'll pay a bit annually in labor, but you'll be using a proven solution that anyone with an alignment rack can deal with.

Unfortunately, since I'm not very knowledgeable about the TT specifically, I'll have to defer specific suspension suggestions to others. What I suggest is to drive other same-type cars that have the various combinations you're interested in. It's *you* that has to live with those combos, not me and not the guy that claims his suspension is the best, and your tastes will vary from mine and his. There's nothing better than actually riding in or driving a car that has a spring/shock candidate. Don't take others' words for it, try it yourself and decide what your compromise is.

And it will be a compromise. "The Ultimate" for the track will be unacceptable for going to work, while a sportier suspension will give you a better handling car without leaving most of your undercoating on the parking lot speed bump or requiring monthly dental visits.

I just thought of something else you really should do with FACOS: have adjustable-end swaybars. In racing, swaybars are a tuning device, not a suspension device; you size the suspension springs to give you the weight balance and anti-roll that you want, THEN you apply swaybars to tune the balance of the car.

If the bars are attached during the suspension setup phase, then a bar may have a load (or "torsion") applied to it, screwing up your actual cross-weights (one end of the bar will lift a wheel, while the other end is pushing down). AFTER the car is set up you install swaybars with adjustable Heim-joint end to install it with no preload at all. If you don't have adjustable end bars, you'll have to force one end into place, preloading it, and screwing up all the work you just did.

For the street, bars are a nice compromise. Since street cars need to have a somewhat-compliant ride, swaybars are a way to make the car "feel" like it has stiffer springs on the outside corner of a turn. When a car rolls, the inside wheel drops relative to the car, pulling down on the bar which pulls down on the outside tire, forcing it into the pavement. It "thinks" it has a stiffer spring. Of course, if you lift the inside wheel off the ground then you've reached the limit of the bar's capability and it doesn't work any harder.

Lots of things to think about. I'd like to think the off-the-shelf "tuners" have put that much thought into their products.

GregA's 2 cents.

http://www.bira.org

A nice explanation of corner balancing: http://www.nsxprime.com/FAQ/Performance/cornerbalance.htm

0TT0 BURNER

I am w/Bilstein HD's in back and it rocks, w/out having too much neg camber @ rear.

gtt

I will avoid them for the mentioned reasons and lack of testing environment. Maybe Eibachs and Bilsteins.

ezprod

Now I am confused. First I thought I would just by H&R Sport Springs get the lowering, slightly stiffer ride and only spend a couple hundred...then everyone started talking about the pss9's and how great they were, etc. And at only 1200, not to expensive, and then this article...

Ian confused now.

gtt

if you don't have a test circuit and scales you may be only "posing". Not to say some have not set them up well but that there is a lot of room to make errors in set-up also and spending a lot of dough in the process.

ezprod

Is that still at all helpful, or would I merely be doing it for cosmetic reasons?

gtt

Larry. I am in a wait see mode but would rather trust a milder approach and not the most radical springs and compliment with a well engineered damper for the application.