Suspension Voodoo

[Jeremy Billiel]

I am LOLing...This is a great thread of all kinds of various items.

Dan the bottom line is your dollar will determine how fast you can go and how technical you want to be. Greg is 100% in relation to struts. They suck in every possible way and you will need to run high spring rates to make it work which in turn requires expensive shocks.

Dave has a totally different suspension design that is much, much better than struts.

A arm cars can spend less to get the same performance on struts because its a superior design. But even A arm FWD cars need big money shocks and springs when you get to the pointy end of the field.

 

[924Guy]

Ah, you think struts are confusing - you should try tuning torsion bars sometime...

 

[wepsbee]

I am LOLing...This is a great thread of all kinds of various items.

Dan the bottom line is your dollar will determine how fast you can go and how technical you want to be. Greg is 100% in relation to struts. They suck in every possible way and you will need to run high spring rates to make it work which in turn requires expensive shocks.

Dave has a totally different suspension design that is much, much better than struts.

A arm cars can spend less to get the same performance on struts because its a superior design. But even A arm FWD cars need big money shocks and springs when you get to the pointy end of the field.

I will be delivering my car to Matt on Sat. I will check with him and have the suspension looked at for suggestions. I am checking with Koni for max springs rates for the struts I have. I imagine stiffer springs are going to result in a car that will have to be learned how to drive.
All, thanks for the input, this forum really helps!!

 

[wepsbee]

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.

Great info, thanks, learning about the car and how it really works is half the fun

 

[rsportvolvo]

Stiff springs on a strut to reduce movement are only required IF it is outside of the operating window. That is dependent on your exact strut layout.

Some struts have a lot of wiggle room within the ITCS. VW's are screwed as are most cars with bolt on struts. Cars with integrated struts have basically a blank check (BMW E30).

For struts:

1. Within the ITCS regulations design a strut to work within it's limited window.
2. If 1. is not feasible then mask the struts deficiencies with stiff springs to limit movement on a lowered car or run a lighter spring and an ARB on a higher ride height car.
3. Buy top notch dampers for item 1. and good enough dampers for option 2.

If you run really stiff springs it's a waste of money to buy high end shocks as they don't move much (dampers only work when moving). Also chassis flex and component stiffness enter into the equation and the benefits will be tough to realize. If you do run a stiff spring get as big a damper piston as you can, like 45mm and up. The stock Bilstein's 36mm won't work as well.

Note: The Pratt & Miller designed GTO-R's and GXP-R's use @ 400 lb/in springs on an SLA (A-arm) suspension with a HUGE ARB (anti-roll bar). That low of a wheel rate seemed to work quite well.

This is just my intellectual masturbation on the subject.

 

[Greg Amy]

Sorry for the quote/response format. I hate it, too, but it's the easiest to attack.

"any suspension can be made to work well once you stop it from moving." Most appropriate as relates to struts...

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.

Not necessarily true. If you disagree, consider the ramifications of using 1100-in/lb springs and no dampers...unless the suspension is truly solid, there is movement that must be controlled via dampers.

..first, a strut car can be make as fast as an "a" arm car.

Only if you can move the pickup points of the suspension components. In Improved Touring we cannot do that. Ergo, by the design of a street-geometry MacStrut car, it will never be able to be as fast as a comparable street-geometry 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.

Well, no. It's something more esoteric about most of them using MacStruts and that that implies.

Third, shocks, shocks, shocks...talk with Lee at Koni...

Si, si, si!

I...purchased a set of 8600 series Double adjustable shocks put together by Koni USA.

Off-the-shelf valving? Those are good for ~500-700 in-lb springs; after that you'll need to revalve them for more rebound.

I have 500 6" Eibachs in the front and 400 7" Eibachs in the back.

Start by swapping the spring rates front-to-rear, and start looking for springs in 50-lb increments up to 700.

The set up will most absolutely be different on Hoosiers than the others.

You're tire-limited, now. You'll never be as fast as the others until you buy Hoosier or comparable.

Greg, at that point in time I was more than willing to pull the trigger on the "better" suspension package.

I know that, Dave, I'm just pulling your nuts.

And, your experience is not relevant, as you followed Greg's Step #1...

Someone else noted (was it in this thread?) about how rates and all that are irrelevant once a tire is in the air. It may work that way in computer simulations and in the book of theory, but in the Book of Reality it most decisively remains important. There are many other factors to consider, such as swaybars (which impart the lifted wheel's suspension forces to the other side) chassis flex (which imparts forces through suspension components), and wheel stiffness.

And in the end, never settle for "what the experts say" because your situation is always different. I can't count the number of times we've made things work that "the experts" say are wrong ("Kakashi, dude" is one of our favorite team sayings... http://www.kakashiracing.com/team.html)

Lots to consider, lots to test.

GA

 

[lateapex911]

John, good point. Reminds me of a funny story. Was in the pits of a Honda team at a world challenge event, and they were swapping springs:
Crew Chief: "Well, lets put some 7s in the rear then"
Crew, "OK"
Me: "700? I would have thought higher"
Chief: '7 THOUSand"
Me: "OH!!!!!!"
Chief: " But that's not really accurate, it's more like 3500 wheel rate"
Me: "Well, that's more like it, LOL"

 

[Greg Amy]

As an addendum to my above post (yes, I've been thinking about it), unless/until you're ready to go to Hoosiers (or comparable) I'm not convinced significant suspension improvements will do you too much good.

Example: in my original build on the NX2000 (c. 2002) I slapped on KYB AGX shocks and standard-issue street spring rates (350F/200R?) This was during my "listen to the Nissan experts" phase...anyway, key note is that I was running Kumho Victoracers...one of the first tracks I drove was Lime Rock Park, and after some testing I was able to get that car down to the 1:03's.

Soon thereafter we switched to Hoosiers. It didn't take long to recognize we needed more spring rates on the car to both control the geometry and keep it off the bump stops. Of course, as we added more spring rate we needed better shocks. We went from those crappy AGXs to some Advanced Design struts (another one of those "listen to the experts" things) and then later on to Kessler-fabbed 8611-based struts. Strangely enough, even with all those improvements - including a new very stiff cage to replace the old bolt-in Showroom Stock one - it took us until 2006 to get the car down into the low 3's, eventually into the 2's...

This was always one of those things that totally perplexed us. Had we bent something we can't find? Had I suddenly recognized my mortality and was driving worse? Was it true that maybe AGXs were a better package for this car? Nope. What it most likely was was that with the lesser grip of the Kumhos we weren't getting nearly the lateral g-force as from the Hoosiers, and as such simply didn't need to control the suspension geometry nearly as much. In effect, without the lateral forces of the Hoosiers we simply weren't getting into that nasty negative-roll center and suspension-bottoming area that we found ourselves in when we Went Purple.

So, this makes me wonder if maybe it isn't time for some soul-searching on your part. If you're going to hang with your current selection of tires, I'd suggest you need to maybe tune some things around without massive changes. I'd suggest your 8611 are fine as-is and maybe we shouldn't look into seeing how the suspension is working with the current grip levels. Then, once you're ready to make the Jump to Purple we then start delving into significant springs, shock, and bars changes... - GA

 

[Andy Bettencourt]

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.

And comparing rates on a DW vs. McS car is not smart. My rates on my DW car would be undrivable on any of our McS ITS RX-7's.

 

[JeffYoung]

The above is very good advice and consistent with our experience in progressively moving to working the suspension harder with lateral gs and travel using Hoosiers and more cornering force.

Edit -- Andy makes an interesting point. We've heard for years that the rates we run on the TR8 (600/300) and Z (500/250) are too high, especially by the Z guys. I don't think so, at all. In fact, I think we could go higher with better shocks. So, Andy, what do you think is too high on a strut based car? Some of it is a structural issue right? How much can the frame rails take? The 8 has some beefy rails, the Z is pretty weedy.

I know most 2nd Gen RX7 guys down here run 400ish front 300ish rear. Lower than us.

 

[John Herman]

And of course, the setup will change as your driving improves and you start to realize you can go through the corners much faster, which necessitates further changes, which allows greater speeds.........Good stuff.

 

[wepsbee]

You'all realize I have understood about half of all this. It will take some time and explanation to get it all. What I do have fully understood is that I need to get Hoosiers and setup and test with just them. So it shall be!!!!

 

[JLawton]

OK, some more to think about........

Following up to Greg's story on the NX and listening to the "experts", the guy who built my car was an expert. He ran 350/600 for springs and broke track records. I've spent the last three years testing and changing, testing and changing. I now run a larger rear bar than he did and 600/825 for springs which is HUGE for rates on a Mac strut car. It goes to show, different drivers, different tracks need different set ups.


Dan, I'm going to make a suggestion that goes a little against everyone else. Unless you are a multi millionaire (and if so, I want to become your best friend) I would stick with a less expensive tire and spend your money on testing and seat time. Hoosiers will start to drop off in 5-8 heat cycles (yeah, some will say they can get 10 - 12 but they're only fooling themselves). Once a tire goes off it's useless for testing. You want consistancy when testing.

One other big factor for me was that I spent years driving cars that handled like crap. I didn't know any better. Then I drove Kirk's Golf and discovered what a good handling car felt like. From there I had a target to aim at. Maybe some sucke.........er ..........friend would let you drive their car..........

 

[Sandro]

I agree with Jeff's last post, and I am speaking from experience.

I am not sure how much seat time you have but I am guessing not a whole lot(please correct me if I am wrong). My recommendation would be to save the money you would spend on Hoosiers and new suspension, and go buy a data logger and kumho victoracers.
I have been running on victoracers from the beginning and might upgrade this year(only because I got Hoosiers when they had the close out sale at $100 each). Who says victoracers are slow anyway, I have kept up with people running Hoosiers and Hankooks(only for my stupid accelerator cable to break with 2 laps to go)

I saved up and bought a data logger and it has cut off more time than I know Hoosiers would have, plus the data logger doesn't wear out. The year when I got my data logger I couldn't enter any races because of schedule conflicts but I did about 10 days of HPDE's at the same track, and boy did my times drop. Once my times got to a point where they leveled out and consistent from lap to lap only then did I start making changes to the car.

Another way to test if the car is at the max, is to let a more experienced driver drive your car. If they are faster than you, their is no real point in making changes until you reach that time.

 

[Flyinglizard]

Hey K.
FWIW, Low drag is zero scrub. Zero scrub for 3degrees camber on a 15in wheel is about 3mm out. Not straight ahead.
Zero scrub can also be called camber vector or camber steer. The tilted wheel pushes the car sideways a certain amount, etc.
MM

 

[Rabbit07]

I have followed a similiar path as some of the others here with my Neon. I recently doubled my spring rate all the way around the car when I was at Sebring in Jan. My wheel rate was not doubled however because I was experimenting with sway bar combinations. The car felt great with more rate upfront, but the laps weren't any better. The conditions kept changing on us the whole weekend, which really was like a week since it was a double. The conditions made it hard to be scientific about the changes. All of this required that I have my already very expensive Dynamic shocks revalved. Fortunatly I have two sets of shocks, so I can have one valved for one spring rate and vise versa. The higher spring rate seems to work very well with mac strut front drivers. I also have lots of experience tuning Mustangs. They have a mac strut front and solid axle rear. They tend to not like lots of spring rate. Moral of the story is to keep an open mind about set up. Try not to get caught up in using half of one guys set up and half of another.

I also agree with many of the others who have steered you towards tires. I tell people all the time that the biggest bang for your buck will come from tires and seat time, in that order. With crap for tires you seat time will mean very little.

 

[Andy Bettencourt]

It goes to show, different drivers, different tracks need different set ups.

I especially like this advice from Lawton. Jeff Young mentioned the rates the RX-7 guys were running in the SE. Our track record holding car is double that. How bumpy are your tracks? Have any karting experience? How quick are your hands? Blah blah blah.

My RX-7 was 550/425. Loved it. Nick's car was 800+ F. I hated it yet we ran the same times.

I also have tested on tires that were cycled out. Thought the setup was all wrong. Add new tires and it became perfect. You have to test on what you will run on.

 

[924Guy]

I especially like this advice from Lawton. Jeff Young mentioned the rates the RX-7 guys were running in the SE. Our track record holding car is double that. How bumpy are your tracks? Have any karting experience? How quick are your hands? Blah blah blah.

My RX-7 was 550/425. Loved it. Nick's car was 800+ F. I hated it yet we ran the same times.

So true; I'm running spring rates approx 50% stiffer than anyone else with my kind of chassis (including the 944's). Got quick hands. My teammate's car has a more conventional, softer setup, with more swaybar; it should be much more forgiving, but not much if at all slower. And a buddy who upgraded from the softer setup to one equivalent to mine in his 944 found it much more nerve-wracking, unpredictable and twitchy... till I explained it all to him. Then he was OK with it, and started going faster right away.

The more spring you pile on the car, the quicker and more immediate the responses get. That's good, when you're talking about turn-in; not so great when you're a less-experienced driver talking about snap oversteer!

My poor wife had to drive this super-stiff setup all through her rookie year. Didn't stop her, though, and she learned to deal with it. I have noticed that her reflexes and hand-eye coordination got a LOT better, a LOT faster! LOL

 

[wepsbee]

Reading and learning alot. Have decided to run shaved Toyo RA1's for dry, Hoosier Hwet for wet. 500lb springs in front, 600 lb in the back. On order
Currently looking at installing an adjustable larger sway bar in back. Of course
none exist for my car so I will get components from Speedway Engineering and fab one up. Question is what type of bar, solid, hollow, diameter, I guess it all depends on what wheel rate you want. Is there anyway to determine an approximate wheel rate required for a car. I am not sure of the attachment points yet so arm length is not final. Do you have to use same attachment points? My current bar has arms only 6" long.

 

[Jeremy Billiel]

Reading and learning alot. Have decided to run shaved Toyo RA1's for dry, Hoosier Hwet for wet. 500lb springs in front, 600 lb in the back. On order
Currently looking at installing an adjustable larger sway bar in back. Of course
none exist for my car so I will get components from Speedway Engineering and fab one up. Question is what type of bar, solid, hollow, diameter, I guess it all depends on what wheel rate you want. Is there anyway to determine an approximate wheel rate required for a car. I am not sure of the attachment points yet so arm length is not final. Do you have to use same attachment points? My current bar has arms only 6" long.

At only a difference of 100 lbs between front and rear you are going to need a BIG SOLID bar with long arms to make that FWD car fly.