Coil springs: How stiff?

[9746Cobra]

How stiff can coil springs (mainly referring to non-coil overs) be on a Mustang (Which can be 3000-4000lbs) before the point of diminishing returns is reached?

How stiff is generally regarded to be acceptable to drive daily on public roads? (subjective I know)

I installed Mach 1/Bullitt springs on my '96 Cobra to stiffen it up some and lower it an inch. They ride just fine, but I wonder if more coil spring (and appropiate dampners) would be okay on a daily driver/OT car on street tires? The mach 1 springs are 250lbs rear, 600lbs front.

How does the relationship between the front and rear springs effect under/oversteer?

9746C

 

[SKMCOBRA]

Both Steeda and H&R have some really stiff race springs. I think Steeda's are around 1000lb spring rate. I have the H&R Race Springs with front progressive rate of 750-850(or somewhere close to that). They are very streetable if you don't mind a stiff ride and do decent at the track

 

[David Hester]

Stiffer end tends to go straight {resist direction change} That's REAL important!
ie stiffer front springs, stiffer front sway bar, more air front*= understeer more
stiffer rear springs, stiffer rear sway bar, more air rear*= oversteer more
* to a point of maximum adhesion, after that you induce slide, which kinda bell curves on you,
When I 1st started racing, stiff springs were the rage. Then people noticed on bumpy courses or when you hit rumble strips (there were few rumble strips back in the 70's), the car got skittery. THEN (now) it is stiffer swaybars and softer springs to allow wheel to follow irregularities in tracks...still hitting rumble strips.
Note shock tuning is REALLY for intial turn in. Once the car sets, it REALLY doesn't matter if you have shocks or not. Stiffer shocks resist intial movement, so less intial roll, and more grip (all the weight hasn't yet gone off the inner tire, so both tires are gripping) Too stiff (see stiff end goes straight above) and you still can't steer. Once direction change has started the car can transfer weight to outer tires and off inner tires so you have more grip on outside and complete the turn.
You can test this with a shopping cart next time you go to a store. Unweight the inside wheels and the cart turns REAL quick. Don't dump the Fritos!
Old fart flash back.
Hey, Greg Remember when dirt bikes had 4-6 inches of travel?
In dirt bikes with only 2 tires we would weight the outside peg to turn in. To turn left, Lean bike left, move butt to right side of seat, put weight on right foot peg, hold left foot out to catch bike if everything else didn't work.
Road racing was different, as many times outside foot would be completely off peg and you held onto side panel with calf of your leg. Ever do that, Greg?

 

[gcassidy]

We didn't have the tires to hang that far off when I started (Dunlop K-81s). But when I retired racing, we were all dragging knees when running slicks. And your process of weighting the outside peg is actually a form of countersteering that we would use to flick a bike into a lean angle faster than leaning it in with body weight. Because of the caster (shopping carts again) effect, if you push forward on the right handlbar, the bike instantly snaps to the right. Then you just catch it before it goes too far.

But back to overweight 4 wheelers. I understand the principle of having a compliant suspension where the springs keep the unsprung weight from reacting to the inertia of the wheel as it traversis bumps, and the motian of the sprung weight is controlled by the dampeners. When you say stiff = straight, I imaging there must be a threshold where stiffer compression dampening makes for slower roll at turn in, so you have more weight on the inside tires. How do folks who know what they're doing find the point where you want the weight on the outer wheels to help with turn in. It's all happening at the same time, isn't it? Oh..now I have to go back and re-read all my stuff about roll centers.

Thanks, Dave. :mj:

 

[gcassidy]

9746Cobra, what are the roads like where you usually drive? That will make a difference on what spring/strut setup you might be able to live with.
I imagine you don't have much frost heave on your roads there in Florida, huh?

 

[David Hester]

LOL
Didn't mean to make you think. :rollseyes
How about this.
Soft springs, soft sway bar, turn the wheel and weight is instantly transfered to outside- that object in motion stays in motion thing. Suddenly you have more work than the outside tires can handle and you um, wallow, squeal, etc.
If we resist that weight transfer, even for a milli second, we get the benefit of slip angle from Both tires. I've got pictures somewhere of the A/Sedan car with 1/2 the inside tire tread off the ground.
Initial turn in

Both tires on the ground. strut/swaybar have resisted weight transfer.
MidCorner, suspension has taken a set, outside wheel has much of the weight, Inside tire is 1/2 way off the ground...not much traction there.

Now if we go stiffer everything is hunky dory-inside and outside tires contributing till we hit a bump and all of a sudden the inside tires that were gripping have nothing to grip. Wheels can't react except to go up. Chassis goes up from stiffness and there suddenly is 1/2 as much grip and you go off line.
PLUS stiffer makes things happen quicker. Think GoKart. As long as everything is balanced things are fine. The CamBird behind me is REAL stiff and changes directions with great vem and vigor-little if any body lean. Don't keep up and it will spit you out.

 

[gcassidy]

Ahhhh, I understand about weight transfering too swiftly. Guess this is why shock tuning is so important when going fast really matters (such as racing).

And as for syuff happening real fast, I've been intimate with "twitchy". I once raced in a 50cc YZR race on a go kart track.

 

[MFE]

What often goes unmentioned in the discussion of whatever version of "stiffer end slides first" is "but only after the gain in camber control has reached its end". And THAT is one reason why stiffening the front of many a car counterintuitively makes it corner better. Another reason is it causes a sharper turn-in, which can cause the rear to rotate, for a net better cornering capability.

 

[gcassidy]

I'm still in the process of learning all the feelings and feedback that my car (on the track) is giving me, and how to interpret/react to them. I've been out with a couple instructors who would be talking about rotation as I was turning in. I understand, in the broadest sense of the word, what that means the car is doing, but where does rotation stop and a spin start? Is the term rotation simply meaning hanging the rear out a bit,which I can see causing a sharper turn in, or is there more to it than that?

And I've spent years at cc.com trying to grasp some of this, maybe I don't have the head for physics that it takes. :shrug:

 

[David Hester]

I agree MFE, you can't say one thing dictates how well a car handles or doesn't Another reason is it causes a sharper turn-in, Ok to a point - see shock setting above-which can cause the rear to rotate, Not so sure about that. You kinda have the chicken and egg thing going on. Does the crisp turnin cause the rear to go out or does the stiff rear suspension resist direction change and try to continue in a straight line. Of course you have to have a direction change for any of it to happen for a net better cornering capability. That's the good part!
With no flex or weight transfer you have a brick. I understand a GoKart with no suspension won't handle if it has too stiff a frame.
"but only after the gain in camber control has reached its end"
Ok. Camber of course is important, you want tire flat when you corner, but I'm thinking a person could set up a soft suspension with enough static camber that they won't rattle their fillings and still end up turning.

Rotation has to do with slip angle of tires. You turn the wheel, the force of the tires against the pavement causes a change in direction Notice you don't go in the direction the tire is pointed, but change in an arc. The rears are even more of an enigma, as they are still pointed straight...but they turn- rather change directions- with the car...don't that make your brain hurt? They have a slip angle, too.
Over rotate and you have put more change than tires can handle and slip angle exceeds grip. You push or spin.

Everyone has done this even if they didn't realize it.
You go into a corner and figure out you have early apexed. You back off the throttle...I hope.. and the front goes down and the line tightens. (Yeah, Greg you can do the same with a throttle foot, but because you have exceded slip angle and are in a slide). Bottom line, You rotated.
You go into a corner and gas it too soon. You turn the wheel but the car is heading toward the gravel pit. You've moved weight (grip) off the front and on to the rear (that pinned in the seat feeling). You just under rotated.
I use throttle off to change direction mid corner in autoX and road racing.
Some people left foot brake, but I think I get more weight transfer with the lift. Some say it kills momentum, but I don't notice but maybe a 50 rpm drop or less. Just like the shock setting, you just need enough to change directions. Doesn't take a milli second.

 

[9746Cobra]

9746Cobra, what are the roads like where you usually drive? That will make a difference on what spring/strut setup you might be able to live with.
I imagine you don't have much frost heave on your roads there in Florida, huh?

There is some smooth highway criusing, but on other roads there is constant contruction in the area. Those areas are rough.

9746C

 

[gcassidy]

Ouch. My head hurts even more. :bash:

But I think I understand some of what you guys are saying...a little. And it's largly stuff I've read in books by Ross Bently and Carroll Smith. But on the track, when changes are happening in milliseconds, I think my brain is working in mega-seconds. :dw:

 

[gcassidy]

There is some smooth highway criusing, but on other roads there is constant contruction in the area. Those areas are rough.

9746C

Between springs and bushings, my car's a bit stiffer than stock. It's tolerable, but I avoid a few roads when I'm out driving. I'm happy with the compromise I've reached, for now. But I'm not even sure what spring rate I have. I put in Kenny Brown Sport springs a few years ago, but lost the info on their spring rate. And I can't find it anywhere on the web, now that he's closed.

I hope you're getting the info you needed.
I didn't mean to start asking the experts for a course in driving 101, as useful as it is. :read:

 

[9746Cobra]

Between springs and bushings, my car's a bit stiffer than stock. It's tolerable, but I avoid a few roads when I'm out driving. I'm happy with the compromise I've reached, for now. But I'm not even sure what spring rate I have. I put in Kenny Brown Sport springs a few years ago, but lost the info on their spring rate. And I can't find it anywhere on the web, now that he's closed.

I hope you're getting the info you needed.
I didn't mean to start asking the experts for a course in driving 101, as useful as it is. :read:

I am. I'm thinking I should try the mach 1/bullitt springs I have now and see how they do before making any changes. The biggest improvment I could make as far as suspension goes would be some Bilstein HD dampners to replace the stockers I have.

But then again, I'd hate to buy the HD dampners and later decide I want a firmer front spring that might be too much for the HD's.

9746C

 

[MFE]

I'm thinking a person could set up a soft suspension with enough static camber that they won't rattle their fillings and still end up turning.

Indeed a person could...just not the usual person driving the usual mustang

I did very well regionally with a very stock suspension on my LX, against competition with bone-jarring suspensions, and I understand your point. The thing is, real-world results are sometimes derived from counterintuitive measures.

And it's not just mustangs...lots of near-stock cars turn better when you stiffen the front, even without stiffening the rear, and even though practically every car sold is biased toward understeer in the first place. And the two biggest reasons why are camber control and transient response.

 

[Gonz]

How stiff can coil springs (mainly referring to non-coil overs) be on a Mustang (Which can be 3000-4000lbs) before the point of diminishing returns is reached?

How stiff is generally regarded to be acceptable to drive daily on public roads? (subjective I know)

I installed Mach 1/Bullitt springs on my '96 Cobra to stiffen it up some and lower it an inch. They ride just fine, but I wonder if more coil spring (and appropiate dampners) would be okay on a daily driver/OT car on street tires? The mach 1 springs are 250lbs rear, 600lbs front.

How does the relationship between the front and rear springs effect under/oversteer?

9746C

I'll throw my 2 cents in. When I bought my '95 GT last year, it had Ford " C " springs on them. I changed those out for H&R Race Springs this winter. I believe the "Cs" are 650 lb/in & the H&R Race are 750-850. When I had the "C" springs I couldn't tell it had "performance springs" on it.

With the H&R's the car is noticeably more quick to respond to steering inputs & the ride is stiffer but not tiresome. It obviously helps with camber as well. It's a better set up for the track.

The ride is such that I don't think about it much while driving. However, "non enthusiast" passenger will certainly take note. You might hear " this car rides stiff." Or even bettter " is your suspension broken?" :bored:

By comparison, back when I had a 1990 LX V8, I put on a set of Eibachs which were near 1000lb springs on it. Those were "too much" for the street for me. Putting in frame connectors helped a good bit, but I wouldn't do such stiff springs again.

That was in 1995 and I was 24. I'd hate to ride on those springs now. 365 days of crappy ride for a few days of autoX/track per year isn't worth it to me.

If you go stiffer than the Bullit springs, make sure your shocks can handle it. If not it will be very "bouncy" and not be a good ride or good performance. Also, if you don't have subframe connectors, putting those in can also make a stiffer spring ride better.

 

[Jimmysidecarr]

I am. I'm thinking I should try the mach 1/bullitt springs I have now and see how they do before making any changes. The biggest improvment I could make as far as suspension goes would be some Bilstein HD dampners to replace the stockers I have.

But then again, I'd hate to buy the HD dampners and later decide I want a firmer front spring that might be too much for the HD's.

9746C

That sounds like a good plan. The 03/04 Cobra front springs are pretty close to that and are in a much heavier car.

I'm running very slightly cut stock springs 1/3 coil rear/ 1/4 coil front with stock isolators.

The SHOCKS will be an important purchase, I believe they will be needed.

 

[TXPD]

My '95 Cobra R was a Steeda developement race car. It raced first as an IMSA Grand Sport(the current Koni Challenge GS class) and then as an SCCA T1(meaning heavy with full interior, carpet and all.)

The spring package on the car when I got it was the race package. 1000lb Steeda/Eibach front springs. 240-260lb Steeda/Eibach variable rate rear springs.

I was perfectly comfortable driving this on the street as well.

 

[9746Cobra]

That sounds like a good plan. The 03/04 Cobra front springs are pretty close to that and are in a much heavier car.

I'm running very slightly cut stock springs 1/3 coil rear/ 1/4 coil front with stock isolators.

The SHOCKS will be an important purchase, I believe they will be needed.

Yea I would really like to get the bilstiens. While I was there though I could install springs like the H&R Race 750-850's. The amount of drop they provide is very similar to the springs I have now. The rear H&R Race springs are about 30lbs heavier than the ones I have now and that doesn't worth spending the money on.

Are the Bilstien HD's enough dampning for a 750-850 rate spring?

I do plan to get SFC's.

9746C

 

[David Hester]

Hey, Rob.