Help - confused by autox suspension recommendations

[Plays with cars]

I am currently running a '74 2.0 in SCCA C-stock class w/ the stock torsions/bars/springs w/ yellow Koni shocks and Kumho Victoracers. Through alignment, corner balancing, ... the car is handling very neutral, but still with a lot of body roll. This year for my own enjoyment, I've decided to upgrade the suspension to address the body roll and reduce lap times even though I know it will move me to CSPw/ the potential for killer Miatas; oh well, I'm there to have fun. If I win trophies, all the better.

I've been searching the forum for autocross suspension recommendations for the last couple of days, but the more I learn the more confused I've become. I understand that ultimately the "correct" setup is different for each driver, but I always assumed the differences would be in the fine tuning, not in basic setup. I've read posts where people are using large torsion bars and sway bars up front w/ 140# springs in back and loving it. I've also read posts from people with moderate sized torsion/sways up front (21/19) saying they need to go to stiffer rear springs (200#+) to get the car balanced. I guess that I'm surprised that after 30 years in the field, a concensus hasn't been reached on the best basic autocross suspension setup for our cars.

Having not yet found the holy grail in the collective wisdom and experience of this forum I thought I would approach the problem from a different angle: the car is currently balanced and I want to maintain that, shouldn't I be able to increase the stiffness of the suspension at each end of the by the same percentage and maintain the same balance?

Using basic formulas for spring stiffness I calculated that replacing my stock torsion and swaybar combo up front with a 21mm/19mm combo would increase front stiffness 230%. In back I want to increase stiffness an equivalent amount through springs only so I can remove the stock rear swaybar. Assuming stock springs are 90# I calculate that I need to install 330# springs on the rear. But this is insane, no one is running anything near this stiff.

The car is not street driven anymore, so ride comfort is not a consideration. Do I really need to put 300# springs on the back?

[914fan]

I am no suspension expert. In fact I have never done non factory suspension work.

Having said that here are my thoughts. I believe you can get away with lower spring weights in the rear. Reason being unless you have superman tires with superman engine power you could load up the rear. most do not. Also when breaking most weight is pushed forward. Those are my thoughts.


I with I could give you a recomendation but I dont have one other than to say you can probably run considerably softer in the rear. i would also think that you will get the most benifit from the front going stiffer. (just like brakes)

good luck

[Alfred1]

I don't know anything about suspension tuning but I found this info in an old Automotion catalog and it might be useful to you as a starting point.

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[Bleyseng]

The shock and spring,sway combo is important as is the desired feel of the car.
Koni Yellows for the shocks with adjustable perches on the rear.
22mm front bars from Weltmeister of Tarrett
21mm front Tbars
200 rear springs
corner balanced

the 180lb springs are progressive so you get some rear wheel tucking so the 200lb spring is a better choice.
I like a flat neutral car that I can control in the tight turns on the AX track or even on a track.

Geoff

[Dave at Pelican Parts]

If you think you might want to stay in C-stock, you can upgrade the front sway bar. It's a "free" mod in stock class. A 19mm adjustable one should work well with the stock suspension components and will give you some adjustability.

I personally am a fan of keeping stock torsion bars up front, upgrading the front sway bar, and going with stiffer rear springs to keep the car balanced. (No rear bar for me, thanks.) The 22mm front bar and 140 lb/in (or 150 lb/in) springs seem to be a good combination. They offer a ride that isn't too punishing on the street, but keep the car fairly flat in the turns.

And I will second Geoff's note that the shocks are also quite important. I like my Koni Gas Sport shocks.

--DD

[Plays with cars]

Thanks for the feedback! The page from Automotion was a good sanity check, 300# springs were definitely out of the ballpark. Reading their specs though, I have to admit I'm a little concerned about how soft they proposed for rear springs in the autocross setup.

Geoff, how is rotation with your set up? I like a little oversteer on throttle lift, that is easily reined in at the apex with throttle application. With my current setup I have to use tire pressure changes and shock adjustment to dial in the balance. I'm looking forward to being able to dial it in with the front swaybar also. Do you run the bar around the middle of the adjustment or are you full soft?

[Bleyseng]

If you are running street tires the setup I have still pushes and will oversteer when you lift.
I mostly run with Kuhmo Victoracers so it really sticks and you control the car in the turns with the throttle and left foot braking. You can feel a spin coming on pretty easy too vs that snap spin the more stock setup has.

Geoff

[Joe Ricard]

BTW you are going to DSP.
I'm up against the same dilema and am just about to stop screwing with it and learn to drive what I got. My driving sucks as evidenced by my 19 yr old son whipping me on his 3d event ever.
But I consistently suck as my times are usually pretty close. Plan on getting the local "hot shoe" to drive my car and see if there is anything haineously out of whack. He can drive a John Deere tractor fast.

[jhadler]

Mark,

The Automotion "recipie" list is really general, and tends to be a good starting point, but really isn't the ideal setup. It really does come down to driver preference. Some people like a car that's super loose, others like a car with just a little bit of push. You will generally be fastest with the setup that you're most comfortable with...

As for the comments so far. Geoff has the right combination there! ;-)

I'm also running the following:

200# coils in the rear.
21mm torsion bars in the front.
22mm sway bar in front (adjustable).
Koni adjustables at all four corners.
15x8 wheels with 225/45-15 Hoosiers.
Poly bushings all the way around.

Alignment:

It's been a little while, but if I recall, I had -1.25 camber in the rear. 6 degrees of caster in the front with -1.75 degrees of camber. Toe was every so slightly out in front, and zero at the rear.

Car is very responsive, and very neutral.

Oh, and you don't have to battle the miatas in CSP, now it's just the Bimmers DSP... It took years of letter writting to the SEB, but I finally got enough people in the right places to consider it, and get the car re-classed. At least now we have a snowball's chance, rather than no chance at all...

-Josh2

[Plays with cars]

Thanks again for the input. I think I'm going to go with the setup Geoff recommended; sounds like it's a proven formula given the endorsements it received.

Joe/Josh - glad you pointed out that we're in DSP this year. I'm not sure that's a good thing for me though, the guy who got third at Nationals last year is in my region and races at our events. Alex is a great driver and his Bimmer is really dialed in. I don't expect I'll be vying for 1st this year.

Regardless, the car is going to be tons of fun this year. I'm in the process of rebuilding the transmission right now to solve the annoying 1st and 2nd gear grind, I have a set of V710s fresh from UPS to replace the three year old Victoracers on the car, and now I have a formula for the suspension (soon to be on order).

Regarding alignment: less body roll = less camber required? Up front I'm running -1.4 now and will probably stick with that. But in back I have -2.0. Do I need to take a little out of it. Toe is exactly as Josh stated: 1/8" out up front, 0 in the rear. Caster is 6 degrees.

[jhadler]

Mark, don't worry, some of us have even tougher competition than you in DSP...

David Fauth is in my region... Well, at least I'll know the high water mark of the class...

Still, DSP is definitely more doable than CSP.

-Josh2

[Bleyseng]

Forget the poly bushings thou, install polybronze or needle bearings in the suspension. Polys require constant teardown to re grease.
The suspension works best without any friction and the polybronze or needlebearings provide that.


Geoff

[jhadler]

Geoff,

It all depends on the rules that you're competing under. In the Street Prepared rules, metal bushings (be they bronze or needle bearing) are quite definitely illegal.

I have poly bushings, and have not found them to be problematic. The trick is to make sure they fit very well before you mount up the control arms. If they bind anywhere, you're gonna have problems. And if there are gaps, same thing...

-Josh2

[Dave at Pelican Parts]

Originally posted by Plays with cars
Regarding alignment: less body roll = less camber required? Up front I'm running -1.4 now and will probably stick with that. But in back I have -2.0. Do I need to take a little out of it. Toe is exactly as Josh stated: 1/8" out up front, 0 in the rear. Caster is 6 degrees.

Correct, less body roll == less camber required. But I don't think 2.0 negative camber in the back is going to be too much, even with a car that doesn't lean as much in the turns. Lowering the car from its current ride height will result in additional negative camber, though, and that might just give you too much... But you'll need to check tire temps to really know.

--DD

[Bleyseng]

Mine are two years old (poly bushings) and fit great when new. Groved them and installed 'em. Time to pull them apart to regrease them as they are sticking. Forget that! I am installing poly bronze witha grease fitting.

Geoff

[jhadler]

Why not just install a grease fitting with the poly? I'm not saying that poly is better, they're not. But for many of us, it's the best we can do under the rules (or the wallet)...

-Josh2

[Plays with cars]

Okay, big decision has been made, ready to buy parts. Diligently searched the Pelican site but I couldn't find 200# springs. So I called and talked to a sales person, they couldn't find them in them in the catalog either.

Dave - a little help here. Does Pelican carry them?

[Dave at Pelican Parts]

Umm... Frankly, I'm not sure! They're obviously not in the catalog, as Weltmeister doesn't make any. We may be able to get them through a different supplier. Check with Tom Gould (tom at pelicanparts dot-com) to see what he has to say.

You can get them through "certain other" suppliers if we cannot supply them. Jason from Paragon is very likely to have them, and will also have lots of good setup advice.

--DD

[jhadler]

If you have Koni adjustables with threaded spring collars (which by the way you should have anyway), then you all need to do is call any one of the numerous spring providers (R&R, Ground Controll, Eibach, etc.) and tell them you want 200# coil over springs, at whatever free length you want. Easy as pie...

If you don't have the coil-over collars for the rear, then you need to look into custom springs, and that gets more challenging.

The coil over springs for the rear are a conventional size, and every one uses the 2.5 ID (?) spring size.

I'll measure my springs tonight if you need the free length measurement. Or I'm sure someone here already knows that number off hand...

-Josh2

[Plays with cars]

Yep, good call Dave. Paragon has a coil over kit, including adjustable perches in their catalog. I feel bad using this wonderful resource Pelican has provided, the forum, to source parts from a competitor.

One last question before I take the leap: will an original tub in good shape hold up to the 21/22/200# combination? The deeper I get into this, I'm realizing this is an aggressive/serious setup, and since I can't do any chassis or trailing arm reinforcement in my class, I'm wondering if this is the right thing to do. Obviously a 17.9/21/180# combination would be easier on the tub and trailing arms. Would I be smarter sticking with a practical setup in this class instead of playing boy race car driver?