Is there any good way of figuring out a reasonable spring free-length?

Right now I'm trying to figure out front, but something applicable for both front and rear would be more useful for everyone. I'll take something math heavy or rule of thumb, I'll even take "I used this height for this # spring in this combination and got this ride height."

 

I likely have too many variables for someone to have the same combination, but I want to end up with a spring with a similar or slightly higher spring rate to factory WS6/1LE springs (mid 7xx lb or so, this is a street car that I expect to handle well but WRT to track time most of it will be dragstrip, so I'll take a slightly softer ride for more reaction on the line, right now the stock WS6 springs which surprisingly still have a stock 4x4 like ride height react well enough at the dragstrip), a ride height similar to Eibach sportlines (about 2" drop) in a front suspension that uses UMI K-member and A-arms, 1" extended ball joints (lowering ride height roughly the same amount) and fabricated weight jacks in the top pocket.

I have 2 sets of Eibach pros that I can try (maybe cut a 1/2 a coil), but I suspect that the hardware/spring cups for the weight jacks will take up more space than the 1" ball joints, and 1/2 coil cut will give me, and I'm guessing that more than that will be too stiff, I have factory ride hight WS6 springs, I have slightly but evenly sagged WS6 springs with 1 coil cut that lower the car about 3" but have a really nice ride, what I believe were some Camaro RS springs (really tall and soft) as well as probably half a dozen others in the garage.

 

No one has ever figured out anything with spring free lengths?

 

Not sure if this is what you're asking, but with my Ground Control Weight jacks, the springs are right at about 9" @ whatever given spring rate you order. Since you mentioned factory spring rates, for my latest car, I ordered a set of GC weight jacks with a set of Eibach 9" springs at 750#. I will also be running .75" taller ball joints. My logic was to modify my suspension geometry with BJ's, and panhard bracket out back, install new shocks/struts, but keep factory spring rates. Fine tune and really see what it does close to a stock ride height. THEN lower....then tinker with spring rates and swaybars. I feel like on past cars I've threw all parts on the car at once, and frankly I don't really know what parts are making what difference.

As G.C. cautioned me about....soft springs with weight jacks can limit your max travel, where normally a stiff spring would keep it under control. Where exactly that coil bind happens isn't exactly a hard spec, but we have pretty good roads around here and GC felt I'd probably be ok. I'm gonna send it and see what happens.

 

This isn't super duper exacting but it was pretty darn close when I was trying to choose spring length for the rear of my car.

1. Weigh the vehicle front and rear. Guesstimate how much is "unsprung" weight (not supported by springs) and back it out of those numbers so you're only left with weight carried by springs. For my car,

Rear weight = 1480 lb
Guess of unsprung weight = 350 lb
Weight on rear springs = (1480 - 350) = 1130 lb
Weight per rear spring = 565 lb

2. Choose a spring rate. For my car I was interested in 180 lb/inch in the rear.

3. Calculate spring compression. Things were fairly simple for me because I truly have constant rate springs.

Compression = (Weight) / (Spring Rate)
Compression = (565 lbs) / (180 lbs/in)
Compression = 3.14 inch

4. Measure distance between upper and lower spring pads at the ride height you want. Probably have to remove a spring from the car and use a floor jack to set things where you want and then measure.

5. Figure out the spring free length that you're shooting for.

Compressed Height = (Free Length) - (Compression)
Free Length = (Compressed Height) + (Compression)

 

Also, remember the front springs have a motion multiplier because of where they're mounted on the a-arm. Not sure what it is for our cars but I think it is around 2.0. So take that into account when calculating weight on springs and changes in ride height.

 

That's EXACTLY the kind of thing that I'm looking for and very close to the range that I'm thinking about for similar reasons. What are you thinking for the back?

750 is actually a bit higher than the official spring rate that these cars started at. The published spring rates for the performance suspensions were in the mid 500's, surprisingly ALL 3 of my cars that I can vouch for the springs that I've pulled out were WS6 cars and I measured their spring rates to be 565, 611, and 623lb/in. What were you planning to use for a rear spring rate? One set of those springs were damaged so I only have 2 numbers for rears, 145 and 155.

I'm asking the question because I'm wondering how short I need to get the spring free heights to work with the weight jacks and be in a useful adjustment range.

I'm doing this because back in the day (in the early '90s) when I did a lot of autoX with my original '83 TA, I had a combination that I loved (I cut the springs till I got the spring rates that worked, and then shimmed them with different thicknesses of isolators to get the ride height right), but the suspension geometry was mostly stock (extended ball joints, relocated PHR, LCA brackets... all weren't a thing on this chassis yet). Right around 800# on the front, 195# on the rear, 32mm solid bar with poly bushings on the front 19mm with rubber bushings on the back, poly control arm bushings in the front, rubber in the back but boxed stock arms, all this ran on 235 and 255/60-15 "street" tires on the street and dragstrip (worked well and was a nice aggressive ride), and 245/60-15 f/r Hoosier road race slicks on the autox and RR (I tried 245/50-16 the same model tires with similar 16" wheels and the car was slower). It was competitive for the time at the dragstrip and autox with just a tire change, interestingly I found that t-bird Koni yellows worked better for everything but RR and the Koni yellows for an f-body worked better road racing.

My current build is also intended to be a do-everything build but I've changed so many things I don't know where to go with things. The whole front end is tubular, the engine is lighter with aluminum heads, 1" extended ball joints. It will eventually get fabricated front spindles, eventually. EVERYTHING in the back is heavier (intended to handle A LOT more power), Moser 9" axle, 35spline axle shafts, nodular iron case, fully adjustable LCA and PHR brackets that I made and much wider rear tires (I typically have 295 or 305 section widths on there now, and I don't see anything narrower than a 275 or a 28x10.5 slick working at the dragstrip). I want it to sit like my '83 did (I called that lowered close to 3" the fender heights were very close to Dean's Camaro) and I suspect that I'm going to end up with front springs in the 700-850#, but NO IDEA what will work in the back.

With the extended ball joints and lowered PHR, the way I understand it I'm going to end up needing things softer at both ends then without them, and the f to r tire size stagger should mean that I'm going to need to stiffen up the rear some in proportion to the front. I'm trying to find a 34mm hollow front (I've never liked how these cars feel with the 36mm hollow in the front, and the 32mm solid that I've liked is too heavy, so I'm hoping the 34mm hollow will give me the 32mm solid feel with less weight) and I want to run as stiff a rear sway bar as I can, maybe find one of the mythical 25mm rear Iroc bars (it will make dragstrip tuning easier, making it a better true triple purpose car). That leaves me with not a clue what to try with the rear springs. What I want to work is the heavy rear bar and springs in the 100-130# range, I know that I can make that work at the dragstrip, but I don't know if I can make that work WELL on the street and ESPECIALLY on an autoX (I'll take a slight compromise on the road course as long as it's not horrible). I'd consider 2 sets of rear springs that get swapped out since they are easy to swap, but I've also been considering using something like UMI's rear coil overs in the back which would make that a no-go. OTOH, it's really hard to find soft rear springs for these cars that fit the stock pockets. I don't know of any for sure.

Ideas???

 

Yeah....750 is a little heavier than stock, but it's the lightest I could get at ONLY 9" tall. My goal is new shocks/struts/springs/BJs, PHB relo, and create a baseline. 750 was the softest I could go.

My rears...not yet installed are 175. That was GC's recommendation with the 750 front. That's being said, I expect I'll need a stiffer spring relative to the front, given the PHB relo. I do NOT intend go bigger on the rear bar, in fact I'll likely try a smaller bar if I go stiffer on the rears. I really don't wanna try and figure it all out on the computer. Following some advice from Dean and Brian and honestly not really listening to other ideas. I know I don't know, and if I don't follow their lead, then who? Right or wrong I suppose, that my action plan. ....and like I said earlier, not throwing it all at the car at one time. Piece by piece, at least as much as realistically possible.

For the record, not saying either of those guys advocated the 175/750 combo or the GC kit. Just basic strategies for setting up the geometry to affect change of the roll center, roll axis and center of gravity. The parts choice is mine, knowing darn well I'll likely spend extra in the process of trial and error.

 

At 750 lb/inch I think that you're going to wish you had an 11" spring. The jacks are going to be screwed up way high. Also, the coils might bind before hitting the bump stops, so that's something to check for after install. Either way, you're probably going to have to increase spring rate as you make the car work better and get more grip.

I'm in a similar boat with 800 lb/in weight jacks. GC sent me 9" springs front and rear and it would have been better with 11" at both ends. Mine are fine for driving but probably not enough if I slap on some serious tires. But the springs are fairly affordable so it's no big deal to buy new sets as ideas change. I have 3 rear sets already (current is 11" tall), and will probably buy another new front set this winter.

 

And you know, everybody's car is a little different so it's fine to just buy something and buy again later as you feel things out and learn. A novice will try to buy once, whereas an experienced person will experiment and buy many times. It's the people that just keep trying stuff that get the furthest ahead over time.

 

Deep down, I think you're right. ....I felt like I had to start as close to stock as I could get, with the softest spring. GC says they've sold those springs and have had success, but he was quick to point out that they don't officially list that as an option, soooo....pay attention to what it's doing as I may choose to go stiffer, lol.

 

I had 9.5" #850 per Dean's suggestion. When I did the LS2 swap and alum rad and .5" ext BJ, I needed a taller spring. Dean thought I was slightly low at #850, but I'm in the ballpark.
Hyperco only offered #100 increments, so I'm at #900 front with 11" coil, now. That is with the swivel cup WJ's. The 9.5" I could pull out with my fingers once the WJ was fully recessed. The 11" springs I put in with a jack - NOT a good idea, but it worked.
I do not want to go #800 or lighter in the front. That said, I can afford some travel with my front RC height. High speed breaking at Road America will give me plenty of front dive at #900!
Too soft a spring invites too much weight transfer along with weight jacking that our cars suffer from. Don't invite too much transfer onto the BJ/spindle. Especially if you do not have drop spindles - you drive the front RC below ground and make steering a muscular event. And then with soft springs out back, you are not going to handle/steer at all.

Every instructor or competitor that I've ridden with, suggested lighter (or no bar) bar and heavier spring in back. That went against my theory, but darn it , it works! Our cars suffer from independent rear action (solid axle), and tying both sides up by more bar is not the route to go. Several JY bars and a couple of rear springs will teach you. Ultimately, you have to have something that suits your driving style, or YOU will not be comfortable.

Coming into a corner, hitting the brakes, your are transferring weight to the spindle/BJ. With that weight transfer, you do not want light rear springs with a strong rear bar (along with solid axle). Along with a platform that is prone to weight jacking. RETHINK IT!

 

Brian, you've been a big help in previous threads, and I don't wanna hi-jack THIS thread, however....real quick... ....I follow your logic. My thinking was by keeping the springs closer to a stock spring rate, but adding good shocks/struts, as well as the BJs and lowering that panhard, I really get a feel for what those changes offered, as I've been regularly driving my bone stock IROC for a few months now. ....from there....I have every intention of making spring changes. I guess when you do everything at once....and when you don't regularly drive autoX or road coarses....it's hard to learn what does what. Springs are relatively inexpensive....this my attempt to learn what does what.

 

Don't be so thensitive! Assert yourself!

A lowering of RC requires a stronger spring, yes. FACT.
The conventional wisdom is to tie down the front, and match the rear to it. Keep this in mind.

Without RC improvements, the front dives into the negative ground. And, the rear springs are sooo soft, that the rear solid axle and strong-ish bar prevents independent movement. One cannot maintain rear tire patch. Well-proven. IMO, more rear ###, and less bar.

You cannot have stock weak spring rates, and have performance or control of weight transfer! They (the lawyers) bake the cake. But we can make the platform perform wonderfully.

Spring rates cannot be discussed apart from shock control rates. They work together. An optimal system will account for both. In looking for a 'ballpark' rate, look at the experts. That only gives you a starting point. IMO, DSE knows what they are doing - just over-priced. Press them for details.

Shocks are timing control devices. They have to be matched to spring rates. This is where the winners and losers are separated.

IF there was an alternative front SB, I would consider a lesser spring rate. So far, it is not economical or practical for a street driven car. This may change!

So, you cannot keep stock spring rates and increase shock timing. They are a pair. Springs keep a set height; and the shocks are a timing device to re-set the ride height in time. Talk to a company that will "re-valve" shocks to spring rates and you'll learn. Good assignment for you.

If you go 150mph into a 90* turn, you can't have all the weight transfer onto the front, with no rear traction at all. Spring rates and shocks (timing devices) will determine traction and comfort. IMO, #850 or more in front, will give balance to the back, and allow for controllable weight transfer to the driver, my opinion. Others may disagree.

With lowered RC's, #850 front or more along with a small rear bar and #250 or more in the rear is an excellent staring point. Personal preferences will dictate the rest. Again, look at DSE, and arrive at your own. Don''t take one person's opinion, mine included, look at several.

Also, be willing to challenge your own theory, and do something different. I am a theory guy, but smaller rear bar and more spring was the answer. It works.

 

Brian, I replied in the thread I started regarding the lowering of the PHB a few weeks ago.
https://www.thirdgen.org/forums/susp...g-panhard.html

 

How much smaller of a (what size?) rear bar did you go with on your setup, or would you recommend along with stiffer rear springs?

 

I went from a stock 24mm bar to a 19 mm bar and #250 rear spring on a coilover.

 

Right now I'm having a bit of an issue following this- essentially you stiffen one corner and you transfer load to the opposite corner. You can do that with a spring or a bar. If you do that with a spring you tend to prevent F/R weight transfer (in this case it would be F to R), if you do it with a bar, you should prevent some of the jacking. I feel like this is backwards of what you're suggesting, maybe it's too early/I'm not awake enough yet, I'm missing something.

I know that there is something to this with on these cars because I remember on my '83 once I got the springs and bars as close to where I wanted them as I could I found that I liked the combination better by putting rubber bushings back on the rear bar softening it slightly more even though I was running smallish rear compared to front bar. OTOH, everyone seems to complain about understeer with most setups on these cars...

I always felt that the smaller rear bar thing was an outgrowth of AutoX rules (f-stock used to allow any front bar but you had to stay with a stock rear, so people would slap the biggest front bar that they could find on it and then make the rest work). I'm betting that 850/250 36mmhollow/19mm would be a pretty happy handling wise on my car, but I'd like to make more rear bar and less spring work because of the amount of dragstrip use the car will see- I care more about handling but I know that 90% of the time that the car will be driven REALLY hard it will be in a straight line.

 

I've been looking at the pile of springs in my garage and I'm very tempted to cut a set of eibach pro springs. Plugging their dimensions into my spring spreadsheet cutting a full coil off of the front ones will get me a spring rate of right around 860# and a free height of 11.5", which should be pretty close to what I would want with weight jacks and 1" extended ball joints. I haven't figured out a good way of figuring the same out for progressive springs in the back (I've never been a fan of them in the back, but I'm willing to try them again, especially for this application I feel that they may work for my handling/dragstrip compromise inclinations), but with specific rate springs you shoot to just over 200# by doing any cutting, so I would imagine that's where I would be cutting these also.

 

Does anyone have any idea what effect cutting coils from the stiff side vs the soft side on progressive springs has? Normally it wouldn't be an option, but I think I'm just going to put a 5.5" spring seat on the axle side also so if I use factory-style springs I'll be cutting the pigtail off anyway.

 

Not a fan of cutting springs, but it can be done.
Dean always preached progressive springs in the rear. With a weak rear spring, you lift a tire on the outside of a turn. Stronger springs solve that; hence, the weaker bar. I didn't think it would work. But darn it, real world experimentation showed me that it works. The weaker bar allows for the control arms to lengthen/shorten via up/down movement for the desired turn-in on the rear. Helps scrub, tire wear, tire temps, too!
NO idea about cutting a progressive spring to what would happen predictably.
For multiple applications, there is no substitute for multiple bars and springs - they are relatively cheap (JY for the bars). Cost of switching applications. Springs are easy to swap out in the rear. Bushings will cost more! With my 12bolt, I needed beefier bigger brackets to keep the SB off the pumpkin because of the bigger tubes: https://www.spohn.net/shop/1982-1992...ation-Kit.html
Splined SB's are the new thing. Makes some sense on the front. Need more multiple manufacturers to make a decision, but waiting.
Not every manufacturer has the complete catalogue. These two Spohn links are decent - don't take that as a complete endorsement, though. Evaluate each component!
The SB links are a good and cheap option on the front: https://www.spohn.net/shop/1982-1992...GM-B-Body.html

 

I'd love to hear a good argument why cutting springs is a problem. As long as you understand the relationship between a spring's length, coil dimensions, rate, and at what point it will yield I see 0 issues with cutting them. There's just so much stupid out there about springs and cutting them, well that's where the problems are.

I'm quite happy to leave Dean out of this and any other threads. What he brings to the table with experience, he completely counters with his attitude and lack of engineering knowledge of why his experience works.

He might be right about progressive rear springs, but I've never been able to get them to work on a 3rd gen. Back when I used to pretend I was competitive I've tried them with all sorts of different combinations, I've even tried them on back to back runs vs specific rate springs on the same day, same course, a few minutes apart and I've always run slower on progressive springs. To me they've always upset a car in transitions. OTOH, I may be willing to try them in this setup because they might be the answer to what I want to end up with. I'm willing to give up the last 1/10 or 2 of handling to have something that 60' consistently and reliably in the quarter. I've come to terms with the fact that I like cars that handle but 95% of my racing is on a dragstrip, and this one is going to have enough power that I've already compromised so much WRT to the weight of parts (9" ford rear with 35spline axles and nodular carrier... probably 50-80# heavier than anything that I would reasonably put back there if it was a 10/10ths handling car)

You lift a tire??? Do you mean you lift a front tire? I read that like 4x and somehow it read like you lift the rear tire, but that doesn't make any sense. For the life of me I can't figure out how a softer rear bar and stiffer rear spring will let the rear react and at the same time limit that reaction. Kinematics and Millican don't work before 6am in my head on Thanksgiving.

Well actually, if you do mean lift the front outside then maybe you're referring to preventing weight transfer to the rear under acceleration out of a turn, but that is also controllable with rear suspension geometry. I guess I need you to clarify.

What I know for sure right now is that the traditional way to make these things work in a straight line is to run a STIFF rear bar and then just enough rear spring to keep the rear from bottoming driving around and then using suspension geometry to do the rest. You can kind of get away with a softer bar using rear air bags to tune in a bias, but that's MUCH touchier, and when it gets messed up it's less pleasant to deal with.

Yea, I'm betting that I'll have to go to the 4x4 guys to find a usable answer. The fact is that progressive springs are not that common in handling applications.

Yea, I got tired of that kind of BS with this 9". When I made the brackets for this one I welded saddles with welded nuts on the back of them to the axle tubes and it's setup to bolt on a set of standard ES sway bar bushing shells with 2 bolts. No U bolts, no having to have 3 hands to hold it all together to bolt it on. Just a 9/16" socket or wrench.

I put a splined sway bar on the front of a TTA years back. It was enough of a PITA that I don't know that I'll try again. In the back, it's similar to the arrangement a lot of drag bars use. I'm not sure it's a compromise that many would want to run on the street. Honestly I'm not really sure why it's an advantage besides making more tuning choices.

Those sway bar endlinks are pretty much what UMI includes with their front A-arms, except the A-arms already have the brackets on them. I've been meaning to take a good look at them to see if you can use a quick-release pin in them to pull them to go drag racing.

 

I do mean the rear tire. This is always application specific, so doesn't apply everywhere. Especially with regard to corner configuration. Remember, it's not just fore and aft weight transfer, but diagonal with roll axis.

I, initially, did not "think" myself into heavier spring and lighter bar. There was a guy on Lat-G with a Monte Carlo (also a TA set-up), that was lifting the rear tire - had vids. Then, I was in a JY saw a 19mm bar which I got for $10. Tried it, and it worked.

Now, you do want some lift to help rear turn-in. When the solid axle moves up and down on either side - you can use that to advantage to help rear turn-in. The lower control arm attachment point distance in relation to each other laterally/ horizontally can slightly shorten on a side giving some slight turn in. Dean called this "roll-induced rear oversteer" (I think). He slightly shortened the actual LCA's (adjustable) in order to accentuate this process a little - every little tweak adds up. I learned a lot from him, and I know he's helped a lot of people locally in Cali. I do think his on-line persona is not a complete picture. Anyway, you want some lift to aid in turn-in, but not to lift completely and lose an entire 4th contact patch hurting steering.

Again, I am not an engineer. I have the ability to take in complex subjects and summarize them - two most difficult, Philosophy and Theology. I can always be wrong, muddled, or miss-state things, too.

This would all happen when you are trying to steer (weight transfer to the front); once you are confident of your apex, you're on the gas and weight transfer back to traction.