Suspension


kjewer1
01-02-2004, 01:32 AM
Figured while I was bored I would try to write something up that covers some of what I have learned about DSM suspensions. As usual, its a vast topic and I dont think I could ever put it all into words, and I dont even know where to begin. But on we go.

First there are differences between the 1g and 2g cars. And they are substantial. The 1g car uses a mcpherson strut type front suspension, where the strut is also the upper control arm effectively. This is not the best setup for performance, but there is one advantage. You can use "camber/caster plates" to adjust those parameters easily. A 2g uses an uppper control arm and the shock /spring are free to do just what they are intended to do. The use of the upper control arm allows the engineers to get the camber/caster rates they want, etc. Its a superior design, but adjusting camber isnt as easy as it is on the 1g. There are 2 lower control arms, the straight being the Lower Lateral Link, and the curved one being the Compression Arm. Also different between the two cars is the shock ratio, wheel ratio, or whatever the hell you want to call it. The way the shock is mounted on the lower control arm determines how much leverage it has on the wheel. The recomnded spring rates therefore will vary substantially between 1g and 2g. If I remember correctly, the 1g rates will be lower. Since the vast majority of my suspension experience is with 2Gs, thats where the rest of this post will focus.

The first thing to adress is the fact that 2G front suspension has very limited travel. If you lower the car at all, you'll be spending a lot of time on the bumpstops unless your springs are very stiff. In circle track racing, I found this gave me a lot of understeer when under hard braking and hard left turn (turn 3). Cutting the bumpstop helps, but doesnt entirely fix the problem. Aside from full on coil over shocks that are shorter than stock, the best thing to do is relocate the upper shock mounts with GCs upper mounts. 100 bucks for the front, and 100 bucks for the rear. Money well spent. You can have a very soft suspension that will feel like a very hard one once you get on the bumpstops ;)

Next one should figure out what the car is used for, in order to determine what setup will be best. For road racing you want very stiff springs and stiff shocks. Proportioned so that the car handles nuetraly, without the factory built in understeer. That means stiff in the rear. Is it mostly street driven? You'll want a softer version of a roadrace setup, but with similar proportions. If its a drag car, you'll want soft in the rear. Too soft for racing with turns. But short times are the key, and rearward wieght transfer will help. Etc. For a street car that goes to the dragstrip, a setup like mine works well. I used 325 pounds rear, 450 pounds front. A typical road race/autox car might use 400 rear 500 front, and a hardcore guy will end up around 500/600 or higher. You can see that keeping the 100 pound spacing will increase the stiffness of the rear in proportion to the front as you go up, giving you more and more oversteer, which is the way most drivers will want it. Understeer is bad. Now on teh street a setup like mine is very firm but still comfortable. I rpefer it that way than in my other cars with nice coushy suspensions ;) 400/500 is going to make the average ricer complain, and 500/600 and up is just plain brutal on the street, no matter what brand or what shock. Some of th cheap ricer kits actually come with rates this high, and can be part of the reason you hear poeple complaining about how harsh coilever sleeve setups are, incorrectly of course.

The next thing to consider is shocks. Not all shocks are created equal. ITs a know fact that while Tokico Illuminas work very well (I use them) once you get over ~350 lbs rear springs they will fail often. At 325 pounds, they last me almost a year. The fronts will fail more often as well over 500 pounds. So if you are looking to go over those rates, the next logical candidate is Konis. They will get pretty harsh at high spring rates, but at least they last. AGXs should not be used on 2Gs, since the body of the shock is 1" longer than stock, eating up more of that precious suspension travel. Non adnustable shocks should be used with coilovers, since even the lower spring rates will just overpower them giving a crappy ride. I dont doubt that all the GC or other coilover "sleeve" haters use non adjustable shocks. ;) Its very important to get a well matched set.

The next best thing is to get custom valved konis. There are a few shops that offer this type of setup, ranging from 1100 to about 1500 in cost. Consider that Illuminas, GCs, and upper mounts ran me ~1050, this isnt much more. They will valve the shocks to your spring rates, car weight, etc, giving great performance, a better ride and the shock will last longer at high spring rates. Another advantage is they can rebuild them. Shocks should be considered a consumable item. I replace my rear ones once a year, but you could jsut as easily have them rebuilt if they are rebuildable. Less money spent in the long run...

The best option, and the most expensive, is true coil over shock setups. JIC, etc. Height is typically adjusted independantly of spring preload, the shock can be valved to the spring rate being used, and its adjustable seperately for bound and rebound in some cases. Expect to spend 1700 and up for a setup like this. The lower end Tiens dont really count here, but I believe thier more expensive option is an acceptable setup. No experience with it though.

Another thing to consider is sway bars. On every type of setup but drag racing they will help. In fact, with stiffer sway bars you can get away with a little less spring rate. ;) In my case, when I decide its time to stiffen up my suspension for some circle track this year, rather than change springs I'll upgrade the sway bars instead. That will increase the effective spring rate in corners, but not affect things in a straight line. Meaning my short times at the drag strip wont suffer. ;)

Tire wear is also an important consideration, in racing or on the street. Most people blame the negative camber you get on tire wear, when in fact its the combination of the camber and the positive toe you also get when lowering a car that will eat up the front tires. I went through a set of expensive tires in 2 weeks when I first lowered the car. I tried a camber kit but didnt like the way it handled, so I took them off. I'm running the full 3 degrees in the rear and 2+ up front. But I had the shop set my front toe to 0, straight ahead. While some toe out will improve turn in repsonse, having zero toe allows my relatively soft tires to last for over 50k miles, and that includes a lot of hard driving and 4 tire spinning luanches all year long. More than I could ask for. ;) Rear toe is not adjustable, but my rears last just as long as the fronts, 50k miles roughly with over 3 degrees negative camber. So again, its not the camber that kills the inside edge of the tire, its the camber PLUS the toe.

So, in conclusion. While the "true" coilover setups are best, people do very very well with a sleeve type setup like GC. Try to avoid the cheap coilover sets though, mainly because they use less than high quality springs like the Eibachs used in the GC kits. A friend of mine has konis and 500/600 GCs if I remember correctly, and he owns the road course on BMW and Porche club track days. With just a 16g. R compound tires have a lot to do with it as well, and we wont get into brakes :D Just remember that it all has to be a matched set. You cant just toss parts together and expect to have firm handling without a harsh ride. Its a delicate balance, but if you choose wisely you can get a competitive setup for decent money, that will provide a good firm ride on the street when your done owning the track. Do the research, and choose your own spring rates. Dont just accept what comes with the "kit" and then complain about how that brand sucks on all the forums. Take responsibilty and choose the right parts.

Thats the short version, but I hope its helpful...

kjewer1
01-02-2004, 01:34 AM
This is apost I wrote a couple years ago in response to a specific thread. But it adds to what I said above.

OK here is my humble but experienced opinion on drops and alignments. First of all you say you dont want any negative camber but want to know how low to go without needing a correction kit. Well you need one or the other. A one millimeter drop will increase negative camber. The question is at what point will it affect tire wear and handling and how much of each do you want. Tire wear first. You can get pretty extreme with neg camber and not wear tires too badly at all. It's toe that scrubs the tread off your tires. All front suspensions have adjustable toe, but not all rears do. Unfortunately I can't help there because I drive a mitsu, mine doesn't let me adjust rear toe (or any camber at all front or rear). I dropped my car two inches and completely ruined both front tires in a matter of weeks before I got an alignment. After just adjusting front toe the tires have not worn noticeably in 5 or 6 months. So if you dont drop more than about two inches and can adjust toe on your car, tire wear is not much of a problem. Handling however will be more sensitive to camber. If your car rolls a lot in corners you need some static negative camber. But remember the lower the car is the further you are into the agressive portion of the camber *curve*. This means that at low levels the suspension thinks the car is leaning excesively and gives more camber almost exponentially. Its not a linear curve. The flatter a car corners (from upgraded suspension), or the lower it is, the less static camber you need. A low car with neg camber and flat cornering characteristics will do a little better. The point af all this is that lowering a car changes how the suspension works compared to how it was designed to work. You need to compensate for those changes if you go lower than an inch or so (where the curve is slow). Sure many people dont change anything and thier cars still run and may even experience no major tire wear problems, but it wont handle at its full potential. Of course if you are only lowering the car for looks then all you need to worry about is tire wear. You can go up to two inches or so if you can adjust toe. Also, I lowered two inches and my 2.5 inch turbo-back exhaust hits everything. As far as the harsh rides people are mentioning here, it depends on the combination of spring rate, shock characteristics, and the weight of the car. If you know what wheel frequency is you know what I mean here. Many people complaining about harsh rides with coilovers are lowering them to the point that they are always on the bumpstops. I only went two inches with eibach springs and my Tokicos are on the bumpstops all day. Thats also due to the design of DSM front suspensions. The only way to get around this problem is to use short-body shocks, and those only come with the expensive "real coilovers". They have actual threaded bodies also and not just a sleeve that slips over a regular length shock. Custom upper mounts also increase travel. Even very stiff springs and shocks will give a good ride if they are properly sized and matched. A lousy setup can be both soft (bouncy) and harsh, though most people think those two extremes are opposites and mutually exclusive. It's all about finding the combination of those things that works well together and works well with your car. It also depends on the intended application. This got a little long, but I hope it helps.

kjewer1
01-02-2004, 02:13 AM
All of this suspension talk got me searching around for more JIC info for some reason. Came across this page at RREs site:

http://www.roadraceengineering.com/jicinfo.htm

LOTS of good info in there about suspension in general. For those of you that arent Old Skool like myself, RRE knows what they are doing. When RRE talks, wise DSMers listen ;) Check out the rant/rave link too. Enjoy the info there, I know I did. They just about talked me into JICs already :D Anyone want a slightly used Tokcio/GC setup :icon16: lol

EclipseRST
01-02-2004, 03:19 AM
Thats the short version, but I hope its helpful...

holy shit...thats all i gotta say, damn, thanks for the explaination

Afrokid
01-02-2004, 10:49 AM
u really need to write a book or something...maybe even make a DSM website?

JoeWagon
01-02-2004, 04:40 PM
Those JIC's are sweet, now if i could just find 2000 bucks lying around.

95_GSX
01-03-2004, 02:36 AM
DSM's are money pits, there isn't anything for these cars that you cant replace with something aftermarket. so much potential, so little money.

FourG63 97GST
01-03-2004, 02:43 AM
cool, I found a good deal on Tokico Illuminas and tokico springs for $450
I'm goin for it :)

kjewer1
01-03-2004, 08:31 AM
If you havent yet looked up the rate on those springs, you/ve missed the entire point though ;)

1qwik4
01-09-2004, 11:30 PM
Yep, visiting this again. Well, I have read the suspension thread and still have questions. :smile: I have a 98 eclipse gst and want to set up the suspension for drag racing. I am a die hard drag racer. I also use my car for daily street use, but my main goal is to hook w/o having an awd. I am wanting to go with a ground control coil over setup with spring rates and shocks. I need to know what spring rate setup I should go with and where I can purchase springs with defined rates. I also need to know a good shock set up with these coil overs. I have a stock set up currently. Thanks in advance.

kjewer1
01-10-2004, 11:13 AM
Well first of all you did a good job of asking all the right questions and including the right info. ;) Gorund controls will be a fine choice, and the good thing is they allow you to choose your own spring rates if you like. ;) They are Eibach standard diamter race springs, so you wont have to worry about quality. You can use either Tokico or Koni shocks (the most common options for 2g), just be sure to decide first since GC has to cut the coilovers to match the shocks.

As for spring rates, I will admit I'm a bit out of my zone here, this being a FWD. Essentially it is the total opposite of AWD. I apologize if I geared everything above to AWDs, I dont remember if I explained the difference or not. Bad habit :biggrin: Where I have to worry about going to stiff in the rear, you want to go stiff in the rear. Your car is also lighter in the rear than mine, so less spring is more stiff, and you dont want the ass end to be skipping all around in street driving. You might as well do an auto-x or RR setup for good street handling, and less weight transfer in drag racing, since body roll is undesireable in either case with a FWD. I would start with 450 front and 350 rear with Tokicos, or 500/400 with konis if you want to go even stiffer. Either way you will likely be running at softer settings in the rear on the street and set full stiff in the rear for launching. But I would talk to the poeple at GC, search for FWD 2g info, and talk to people that race FWD 2Gs if at all possible. Road race might be worth giving a call too since they do a lot of racing. Unfortunately I have no firsthand experience with FWD 2Gs, and can only estimate what will work based on what I know about the AWDs and the differences between the two. :smile: Hope it helps though.

-Josh-
08-12-2005, 02:47 PM
Found and Stickied

99MITGST
11-27-2005, 02:35 AM
Which brand coil overs would you recommend for a 99 gst being built for quater mile racing?

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