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Thread: Suspension Voodoo

  1. #1
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    Default Suspension Voodoo

    I am now trying to understand the voodoo racers call "suspension setup".
    I truly understand suspension is undefinable due to its drivers "feel" component.
    However there must be starting points.
    Springs heavier in front or rear and why. Do spring lengths matter or can I
    adjust the coilovers to make up the difference?
    Camber in front and back, same camber to start prior to testing???
    Car low as possible or raised, tight as opposed to loose?? Low car would seem to be faster but would the car be too tight with no give?

    I know testing is king and will be attending a test day but I do not have unlimited
    funds for testing or even tires so if I can glean alot of this info ahead of time it would help.
    I assume most of you have gone through this so I am asking for some lessons learned.
    Thanks
    Dan Deyo
    92 Acura Integra
    ITA #94

  2. #2
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    Step 1: Buy a car that has a real suspension, not MacPherson struts.

    Step 2: If no Step 1, then reach into pocket and buy best shocks you can afford.

    Step 3: Buy stiffest springs Step 2's shocks can control.

    Step 4: Realize this is stupid and go back to Step 1.

    GA

  3. #3
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    That goes contrary to the advice I've received Greg (besides step 1), but recognized there are quiet a few variables. When speaking with Lee at Koni about various shock packages, he actually recommended that I didn't purchase the "better" shock package due to diminishing returns. There were also other packages which had a multiple ways to adjust them which I simply am no where near ready for. Given my particular situation, having single adjustable shocks was the way to go. Koni also obtained various pieces of information about my car such as total weight, corner weights, and so forth.

    What suspension brand are you using now?
    Dave Gran
    Real Roads, Real Car Guys – Real World Road Tests
    Go Ahead - Take the Wheel's Free Guide to Racing

  4. #4
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    Quote Originally Posted by gran racing View Post
    ...speaking with Lee at Koni about various shock packages, he actually recommended that I didn't purchase the "better" shock package due to diminishing returns.
    That's because he knows you're a cheap f**k...



    On edit: sorry, I meant to use the word "thrifty"...damn Turet's keyboard...!
    Last edited by Greg Amy; 03-10-2010 at 03:36 PM.

  5. #5
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    Wow Greg, a bit cynical?
    Greg is correct in most of this. However, if you are going to run a Strut type car there are things to be careful about. If you lower the chassis too much you can play hell on the roll center. This in-turn increases roll moment. With very heavy springs you still will not be able to keep the car from rolling or even jacking. You really can’t spend too much on shocks, but for IT racing you have to budget it. You can hit a point of diminishing returns so to speak. Most cars run more spring rate in the rear which seems to help. Ask a good chassis engineer and they will tell you it doesn’t matter once the rear tire is in the air. Once the tire is hanging you are at 100% weight transfer and the front springs are all that matters. Spring and shock lengths matter, you don’t want to bottom out or bind either one. Because you are fitting a poor camber curve you will need to run lots of static camber, but this will depend partly on tire choice.
    Chris "The Cat Killer" Childs
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  6. #6
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    Quote Originally Posted by Greg Amy View Post
    Step 1: Buy a car that has a real suspension, not MacPherson struts.

    Step 2: If no Step 1, then reach into pocket and buy best shocks you can afford.

    Step 3: Buy stiffest springs Step 2's shocks can control.

    Step 4: Realize this is stupid and go back to Step 1.

    GA

    I LOL'd.
    Chris Raffaelli
    NER 24FP

  7. #7
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    Me? Cynical? You don't know me too well...

    Tell you one thing: had I kept the NX I'd have dropped a $6k set of Koni 2817 struts all the way around on that thing...and it would have friggin' FLOWN around Road Atlanta!!! Instead, I had to "make do" with custom-valved Koni 8611s (valving and spring rates, I might add, that Lee *still* doesn't understand how I made work)...

    Just sayin'.

  8. #8
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    I think it was Sir Colin Chapman who once said "any suspension can be made to work well once you stop it from moving." Most appropriate as relates to struts...
    Vaughan Scott
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  9. #9
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    The suspension is only a means to keep the tires happy. Learn to read tires and you'll be steps ahead of the competition.

    Set camber based on tire temps across the tread
    Toe is for tracking and turn-in (toe-out front, toe-in rear generally)
    Caster is suspension layout specific. Struts require more caster to work (emulate BMW & Porsche if you have struts).

    Depending on your technical background and desire to play with numbers you can read up on suspension design via Milliken's, Rowley's, Puhn's, and Smith's books.

    One caveat to Greg's comment on dampers & springs. A damper only works when it's moving. If you are sprung as stiff as a go-kart then dampers really don't matter that much.
    Last edited by rsportvolvo; 03-10-2010 at 04:58 PM. Reason: grammar
    David Russell
    IT Volvo 242

  10. #10
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    A couple of comments..first, a strut car can be make as fast as an "a" arm car. Second, front drive cars like a lot more spring than a rear wheel drive...something esoteric about keeping the inside front wheel planted. Third, shocks, shocks, shocks...talk with Lee at Koni until he gets tired of you. He should have a good deal of knowledge of spring and bars from the old escort series. CB
    Chuck Baader
    White EP BMW M-Techniq
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  11. #11
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    I have spoken to Koni and last year purchased a set of 8600 series Double adjustable shocks put together by Koni USA. They made a tremendous improvement but I think not enough.
    I have 500 6" Eibachs in the front and 400 7" Eibachs in the back.
    I just installed rear camber plates and have not yet had the car on the track so the test day is going to be busy.
    The car to me feels a little whippy and rolly, New technical terms, so I thought stronger springs might be in order.
    I experience some understeer in tight corners.
    I will be using up a set of TA-1's and 888's then I will be using Hoosiers.
    Will the setup be different for different tires??
    BTW great help by all, Thanks
    Dan Deyo
    92 Acura Integra
    ITA #94

  12. #12
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    The set up will most absolutely be different on Hoosiers than the others. I'd recommend NOT using the TAs..just toss them, you'll end up chasing your tail. And i know you don't want to hear this, but I'm thinking the 888s are a waste too, if you're trying to dial the car in.

    If you can buy Hoosiers in your size that have some cycles, that would be better. Of course, you'll still have people suggest that setting a car up on used tires is a waste, but, it's better than setting it up wrong...and I imagine you won't be putting fresh ho hos on every other session, so.....
    Jake Gulick


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  13. #13
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    Quote Originally Posted by lateapex911 View Post
    The set up will most absolutely be different on Hoosiers than the others. I'd recommend NOT using the TAs..just toss them, you'll end up chasing your tail. And i know you don't want to hear this, but I'm thinking the 888s are a waste too, if you're trying to dial the car in.

    If you can buy Hoosiers in your size that have some cycles, that would be better. Of course, you'll still have people suggest that setting a car up on used tires is a waste, but, it's better than setting it up wrong...and I imagine you won't be putting fresh ho hos on every other session, so.....
    Correct new tires every race are not quite in the budget.
    I do have a set of used Hoosiers that was on the car the last race. I did notice, or
    my confidence noticed, an improvement in handling.
    Dan Deyo
    92 Acura Integra
    ITA #94

  14. #14
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    Greg, at that point in time I was more than willing to pull the trigger on the "better" suspension package. Thing is better for a person who knows how to tune it isn't better for a hack like me (or Dan, no offense) who is just learning this stuff.

    Dan, call Koni and speak with them about what's going on and get their advice. Also contact Matt and hire him to do a test and tune day. Get it close then focus on your driving. Not at all saying shouldn't learn how to tune the car, but guarantee that the car is plenty capable of going faster as-is.
    Dave Gran
    Real Roads, Real Car Guys – Real World Road Tests
    Go Ahead - Take the Wheel's Free Guide to Racing

  15. #15
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    I'll try and give you a little more concrete info to help you "hack" the suspension. I raced a very nose heavy, strut FWD car. Lower the front until the lower control arms are level. Ideally you want as much travel as you can get, so after you lower it, look at how much space is between the top of the strut and the bottom of the strut mount. This will let you know how bad the situation is, and whether you need shorter struts. Lower the rear so the car is about level. Check to make sure your rear suspension also has some travel. The limiting factor on my car (not the same as yours) is the travel in the rear. This is a FWD car, so you need to pay attention/focus on the front end esspecially. Spring rate, I'd start with spring rates equal to the corner weight. So if you have 600 pounds on each front corner on average, use a 600 lb/in spring. Disconnect one of the sway bar end links, but keep it there to experiment with it easily. I raced with a front bar for many years, but eventually tuned the car to eliminate it. The first few times I tried this, I was actually slower! For the rear (unfortunately I don't know your suspension design), but I'd shoot for a wheel rate (not the same as spring rate) 1 to 2 times greater than the front. Use a BIG rear bar. Depending on bar diameter availability, this can be balanced with spring rate choices. Adjust the toe on the front to be 1/8" out. Adjust the rear to be straight ahead(that's where mine has always been). Yes, some people will toe the rear out to help the turn-in, but this ultimately makes the car a bit unstable, and at your point, there is no reason to make the car harder to drive. Put about -2 deg of negative camber on everything. Adjust tire pressures using a tire pyrometer/read the tire wear. Don't set it based on what everyone "thinks" is right. Get the best double adjustable struts/shocks you can afford which will work with these spring rates. You will use the struts/shock adjustments to fine tune the turn-in and other transcient manuvers. Use the springs/bars to tune the steady-state handling. Eliminate all the rubber parts you can, as things will easily deflect with the loads you are putting on them, and the shock/strut adjustments won't do much if rubber parts are flexing away. A cheap way to check suspension travel is to put a zip tie around the shaft of the strut and drive it hard. See how far the zip tie was pushed up the shaft. You DO NOT want the suspension to bottom out in corners. I think this should get you close, with a good steady platform from where you can start tuning things. To be REALLY fast, it will be about all the little tweeks that will be needed as you learn to drive and more importantly "feel" what the car is telling you. It will take time and don't be afraid of slowing down while you experiment. Note my comment above about front bar removal. Good luck.

  16. #16
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    First of all, you want the heavier springs in the rear.

    My suggestion:

    1) Buy an ITA Miata
    2) if not, with draw a whole bunch of cash
    3) Give it to Matt
    4) Let him set it up.......


    Hmmmmm. I feel like I'm repeating myself............
    Last edited by JLawton; 03-11-2010 at 07:55 AM.
    Jeff L

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  17. #17
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    Quote Originally Posted by gran racing View Post
    Greg, at that point in time I was more than willing to pull the trigger on the "better" suspension package. Thing is better for a person who knows how to tune it isn't better for a hack like me (or Dan, no offense) who is just learning this stuff.

    Dan, call Koni and speak with them about what's going on and get their advice. Also contact Matt and hire him to do a test and tune day. Get it close then focus on your driving. Not at all saying shouldn't learn how to tune the car, but guarantee that the car is plenty capable of going faster as-is.
    None taken, I agree
    Dan Deyo
    92 Acura Integra
    ITA #94

  18. #18
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    We race a Golf III (front struts, rear suspension design doesn't matter 'cause it doesn't move) and ended up somewhere near where John H describes a path heading toward. We ended up with the stock rear bar and TWO additional bars out back, 700# rear springs and 500# fronts with no bar. To be fair, we focus on enduros so strive for "comfortable" over "all-out fast." We run with just a touch of front toe-out (like damn near none) and the rears straight ahead, mostly to minimize drag. We ended up with (I think) about 3* of camber in the front and about 1.5* in back. Greg might remember better (he conspired with Cameron Conover to make some changes while I wasn't looking) but the temperatures did *not* warrant that much negative camber. HOWEVER tire wear over as long as 6 hours at a time DID. They are beee-utiful when they (Hoosiers) come off.

    I'm pretty "thrifty" myself so we use custom-valved Koni "yellows." They've proven to be pretty OK but yeah, we could probably have more control with trick multi-thousand $$ units...

    Re: spring length, you can do the math to determine how the strut/shock travel and "coil bind" lengths compare, to get some sense of what is going to happen when things run out of travel. Also think hard about bump rubbers. I think they are VERY important, as they moderate what happens as things get close, essentially adding spring rate and damping the crash if/when the shock runs out of travel.

    K

  19. #19
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    First of all, you want the heavier springs in the rear.
    See, if only suspension and tuning topics were this easy I'd actually get it. LOL With the suspension design on my car, Koni recommended running higher spring rates in the front. Curently I'm using 750 lbs front, 600 rear with a stock bar and have no problems getting the tail to come loose. My original suspension was running 400 lbs front and 600 lbs rear.
    Dave Gran
    Real Roads, Real Car Guys – Real World Road Tests
    Go Ahead - Take the Wheel's Free Guide to Racing

  20. #20
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    I did a search, and the 1987 Honda Prelude uses a dual wishbone front suspension. The Ford Escort is using a MacPherson strut. Two completely different animals. Thus, this now gets into the technical difference between wheel rate and spring rate. We buy our springs (and brag about the monster rates we use) using spring rate, but the tire cares about the effective spring rate (aka wheel rate). The suspension is nothing more than levers and springs. Depending on where the spring is placed in the design of the suspension, determines how "hard" it is for the wheel to move up. Do a quick internet search on "wheel rate versus spring rate" to get more. Sorry, just don't have time to go into more details myself.

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