steelcomp

Hey F1...I don't know if you remember me from a few years ago. I (and several others) got ridiculed for putting "coilovers" (I call them coilovers...they're really not) on my car.

The travel isn't as much of a problem in the front as it is in the rear. From wht I remember, these cars were originally designed with an IRS, but when Ford scrapped that idea, they didn't change the chassis design to accommodate the live axle. When I see someone with a radically lowered S197 Mustang, I KNOW it can't handle very well except on highly controlled track conditions, and with extremely high spring rates. I have the Eibach bump stops which sit on the axles just under the chassis cutouts and with my car as low as it is, I have about 1.25" of travel before they contact. They're soft, so the compression allows another 1/2" of travel. but that still isn't much. With my 200# rears, and probably more compression damping than I really need, I bottom on several bridge crossings on 101 north of Santa Barbara, which is really annoying. I'm thinking of bumping up to 250# just to see what the difference is. Fortunately with double adjustables, I can leave the compression where it is, or even go a little softer, and add a little rebound for the increase in rate. I dont think it'll change the balance much...maybe loosen it up a smidge which won't hurt.
Over 100K mi. on the Konis!

F1Fan

Hi Steelcomp,

Of course I remember you 100K??? Geez-Louise you are driving a long way to work! So what spring rates are you running on the GC c/o's in front if I may ask?

For a normal street car the S197 works pretty well with conventional struts and aftermarket springs but only if you buy the right parts and are willing to have a near stock ride height. For those more committed to serious road course handling coilovers are really the only option. There are some nice looking SLA front ends to buy but IMO they are not strong enough to make it in the day in day out street duty cars. The strength reliability and simplicity of a coilover or conventional strut are a big advantage in this way and can be setup on the track to work nearly as well at a huge cost savings especially when running DOT legal tires.

But you are correct, for a hard core handling freak coilovers are an excellent solution to the problem of spring rate options and ride height. Of course as you mentioned at the rear ride height is limited by the over axle frame rails of the sedan based chassis designed for the Jaguar/Linchon sedans IRS so you really cannot go as low as you might like to which gives the S197 chassis a pretty steep rake if you lower the ride height on shortened strut bodies. I've found the S197 likes to be low in front but not too low even with a good bumpstop kit installed. Front control arms almost parallel (1 or 2 degrees) to the ground and no lower seems to work very well.

On my own car with staggered 9x19/10x19 Saleen PJ wheels with 245/45x19 front and 275/40x19 rear tires with a Saleen Watt's link on the rear axle the car seems to like a lot of front spring rate and lots of roll bar stiffness. This combination surprisingly allows me to run minimal static camber and yet still not understeer except in the slowest corners. The Saleen Watt's links come with a gi-normous GT500 rear anti-roll bar but with the raised rear roll center of the Watt's link the car was way too loose/tail happy so I went to Steeda's smallest 20.5mm rear bar which seems to be a very good setup.

I'm currently on single 2.5" ID 10"x350lb/in Hypercoil springs in front and single 2.5" ID 10"x250lb/in Hypercoil springs at the rear. I'm in the middle of rebuilding my M3's suspension around a set of TC Kline Racing double adjustable coilovers, I need to have Koni West machine some new struts and rebuild them but I'm still measuring the suspension travel, bumpsteer etc. to get a handle on the M3's suspension geometry before I give them the specs I need and spring rate to use for setting up the valving. Once I have the M3 back on the ground I want to go to a 2-piece spring setup for the Mustang to get the ride height down to where it works best and the rear axle doesn't roll oversteer but acts neutral or roll understeers instead.

You are pretty low in back especially considering that you have the lower Eibach bumpstops. I don't know how much front spring you have but rather than try to use spring rate why not just crank up the rear ride height 1/2" to give you some more breathing room on the axle bump stops? My car on the 250lb/in springs is getting sort of skittish even with the dampers turned up or down. I have to crank the front damper rates up to keep the car from hobby horsing too much. Of course this makes the ride rather "firm" for most folks. It's not bad but the car was much smoother on the 200lb/in rear springs.

Cheers!

steelcomp

Hey F1,
I'm running 385 on the front for the street. If I back the compression damping down a 1/4 turn for the street (from where I like it on the track), they're not bad at all. On the track they're great, but I also have a set of 435's that I like even better. Less nose dive under hard braking and the balance seems to not change much except like you say...some slight understeer on slower corners. I can just put the front roll bar back to soft if need be.
On the rears, today I went a click stiffer on the compression damping and drove around for a while. I think somehow I had gotten the rear a little too soft on compression because it seemed a LOT nicer. I still might bump up to 225's for the street. I'd like to have a set of 250's for the track to help balance out the 435's on the front, or then, even go to 550's on the front. I know more than one track 'Stang (S197) that runs 600's, and one that runs 700/250, but he's also running remote reservoir shocks of some kind, and probably true coil overs on the rear.
As far as my ride height...I'm 27.0" from the ground to the fender lip on the front, and 27 3/16" to the rear fender lip. The rocker panel is parallel with the ground. Not excessively low, but low enough. I don't have trouble in and out of 99% of drive ways or over speedbumps. For looks, I'd like to lower the rear another 1/8th, but just can't justify it with the limit issues.
It's getting time ot rebuild the Koni's and when I do, I think I'm going to have them add a just a little more low speed damping on bump and rebound. Just a touch more rebound than bump, especially on the front. I'd also like to move the adjustable range more in the middle of my spring rates. As is it, I'm only 5/8 to 3/4 turn off full stiff rebound for these springs, and only 2-3 clicks off full soft for the bump. I'd like to be more in the middle of the adjustment ranges. Any thoughts?

socalwrench

Whoa, come back after one day, and there's two pages of posts.

All I can say is, Just1Guy, is exactly what his name says- just one guy who doesn't have the proper knowledge or experience with springs. I appreciate your time and clarification SteedaGus and F1fan.

It does seem that the debate over spring rates is never ending, which is one of the reasons I started this topic so long ago. And, in the future, I would appreciate it if any future member would not take individual segments of my original posts, which could lead to incorrect assumptions- it's simply misleading.

Just1Guy

It doesn’t take any wisdom to make such comments. A five year old could do it. But backing them up is an entirely different matter.

So here is your chance, back up your statement based on what I have posted. Facts only please. You can save the “smoke and mirrors” for your customer base and your ego.

steelcomp

Nothing Just1guy posted was incorrect. You can debate application and even sometimes effect about springs, but terminology, rating, construction, etc. isn't debatable. A spring's rate is what it is, regardless. It's either linear, or it's not. Even progressive springs have rate curves, so just saying a spring is "progressive" doesn't really say much. Giving "working numbers" doesn't tell you the whole story about the spring, either, since the (progressive) spring's rate change is never linear or even. Two progressive springs with the same "advertised" rates can have completely different curves. Additionally, the application (where most of the debate is) does not change the spring. It may change the working range of the spring nad thus the effect, but at the end of the day, you set that spring on a bench, and it is what it is. Progressive springs are a sales gimmick and a band aid, IMO, and a poor way to accomplish what they're trying to accomplish.

A spring's rate is a spring's rate. Period. It's not going to act differently in any application. Different suspensions may act differently with the same given spring rate, (duh) but the spring will be the spring will be the spring.

F1Fan

This is all correct. In the end progressive rate spring curves are not so much really progressive as "bumpy." I've tested several progressive spring designs and the curves generally will show a soft linear looking rate with a sharp ramp that bumps up to a higher rate over a very short range of compression and then looks very much like an ordinary linear rate spring.

That said I cannot say that what they are doing is completely wrong given the limitations they have to work with. It's the only way to keep the stock fixed spring perches and lower ride height and try to compensate for the loss of travel with an increased spring rate. But the progressive rate springs are a pretty large compromise in terms of function and suspension travel.

Cheers!

Norm Peterson

Aren't they only trying to simulate a coilover's main spring + tender spring arrangement? Just that it's probably more difficult to keep out of the soft rate over the range of suspension travel that an enthusiastic driver might be expected to use. (I'd call these things "bilinear" to distinguish them from true progressives, IOW a third category that many aftermarket springs fall into.). The word "progressive" simply has a better marketing sound to it, and many (most?) customers wouldn't appreciate the difference anyway.

steelcomp - springs are simple, but only as long as the assumptions that you initially make about their behavior remain valid. Sometimes they don't.


Norm

steelcomp

While some are truly progressive, with the type of progressive you're describing as "bi linear", (not a bad description) the section that coil binds (like the tender spring) isn't a separate spring, and is still an active part of the suspension and the rate is still progressive...radically progressive at that point, where a tender spring isn't meant to be an active part of the suspension. A good example is the Eibach Sportlines. The first few coils of those springs coil bind once they're at ride height (much like a tender spring as you point out), but I have to wonder about suspension extension, and unloading that section of spring and how that's effecting things. (suddenly the damper valving is completely wrong) I think that's what you're describing. With a tender spring, hopefully you're never really unloading the tender spring...it's in there more as an active spacer but doesn't have enough rate to effect anything should you unload. I don't have tender springs on my GC's and every once in a while when I'm getting real aggressive, I can hear a spring settling back into it's pocket with a bang. Limiters would solve the problem, but it happens so seldom I don't worry about it.

Because of the applications, I understand the reasoning for progressive springs, I just don't agree with it except on a marketing basis for looks only. Because factory compression damping is usually more aggressive than necessary, using an appropriate linear rate spring to match a lowered ride height would result in a pretty rough ride without an adjustable damper. It's clear that to maintain a decent ride, these linear rate "lowering" springs that are available just don't keep the suspension off the bump stops. Enter- the progressive spring.

As far as assumptions about springs and their behavior, again, sticking with linear rate springs eliminates the need to assume. With progressives it's all a guess.
JMO

Norm Peterson

Yes.

It means that the spring changes radically from one more or less linear rate to a substantially different linear rate at some point. If this happens when there isn't much wheel load (like a C/O that could use a tender spring every so often ) it may not matter much. But if this sharp transition happens right around static ride height that's when you'll be all the time alternating between having either too much damping for best ride or too little damping for best grip. Or damping that isn't really right for either. Separate from damping, corner weights and understeer/oversteer balance will suddenly shift at least a little (not that most guys on springs like Sportlines would be likely to notice).

I suppose that could be mitigated by using a shock whose damping is also position-sensitive and for which you could set the position where the shock damping switches over between mild/moderate and firm to match where the springs do the same. But putting one band-aid on top of another when it's only the people interested in performance that would care (or even want to consider dealing with yet another fussy adjustment - or dampers that would have to cost still more) seems pointless.

I think the amount of lateral load transfer carried geometrically drops as the suspension moves into bump, so there probably are cases where true but mildly progressive springs would be useful.



What the numbers here should probably be used for is as the basis for comparisons and judgement calls. Not as absolute values in a pass-fail numerical evaluation. They're only one part of things like a car's understeer budget, ride frequencies, and flat ride behavior.


Norm