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post #1 of 17 Old 03-15-2019, 04:03 PM Thread Starter
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Spring Rate Help

Brothers car, 90 LX. Full weight. MM control arms with stock K. Currently running 200/12 springs with Tokico D-Specs. Problem is, springs are too soft. If the car is sitting down hill, looks like it has -3 camber. Coming to a stop with spirited brake, rubs the air deflector on the ground. We're assuming it's due to the MM control arms, which have no bind in them. You can swing them up, and they just fall back down with no strut even in them. You can bounce the front of the car with one hand quite effortlessly.

So we're just trying to make the car more drive-able and less like a school bus as it's mostly a street car. Would stepping up to a 250 or higher, make it perform more like the stock location, stock springs?

Any other thoughts from you suspension guys on here would be appreciated.


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post #2 of 17 Old 03-16-2019, 05:48 AM
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Sounds like a drag racing setup, at least on the front. Why don't you call MM.


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post #3 of 17 Old 03-16-2019, 08:35 AM Thread Starter
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Originally Posted by The Blurr View Post
Sounds like a drag racing setup, at least on the front. Why don't you call MM.
Well, to be honest it's def. most drag oriented, but its a street car. He did contact Jack Hidley, who said a 150/14 spring would be the closest to the stock spring in the stock location. We're not understanding this, as the 200's that are in it now seem way too light. So how is a 150/14 going to stiffen up the front over a 200/12?

When asked, he still replied back that a 150 would be the way to go. Doesn't make any sense, which is why I thought I would see what you guys had to say about it.

He simply wants the front to act like it did with the stock springs in it, but with the coilovers for the ease of adjustable ride height.

I know previously someone had talked about the math/science behind figuring out spring rates, but have not been able to locate the info.

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post #4 of 17 Old 03-16-2019, 04:34 PM
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Fox88,

In your brother's e-mail to MM he asked "...what would you recommend for your front coilovers that would be equivalent to the stock ford front coil springs..." That is a 150lbs/in coilover spring.

It is not possible for the front suspension to act exactly the same way with coilovers as it does with springs mounted on the FCAs. In addition, the car has nonstock FCAs, which have different bushings and different ball joints. It also has c/c plates, so the alignment is probably different. In addition, I'm sure that there are other differences in the car that could change things.

Some of the information that your brother provided in followup e-mails doesn't make sense to me, so I asked follow up questions to him. He has not answered all of them yet, but said he would get back to me.

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post #5 of 17 Old 03-17-2019, 08:43 AM Thread Starter
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Jack, I was hoping you would chime in.

Maybe he didn't explain correctly what he's trying to accomplish. I don't know. The stock suspension has "X" amount of stiffness to it, with the stock springs, struts and FCA's. He now has the Tokico's with 12/200's and your FCA's. It now has "Y" amount of stiffness. It's waaaaaaaaaaaaaaaaaaay lighter than what the stock setup is. So the confusion is, how is a 150/14, going to make the front suspension stiffer (to get "Y" back to "X") over the 12/200's he's using now?

He's knows it's not going to be exactly the same, but wants a spring rate that will closest get him to what it was the way it came from Ford. Surely someone has some kind of data on this. If not, he's just going to put all the stock stuff back on the car, because what he has is just too problematic for street use.

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post #6 of 17 Old 03-17-2019, 03:55 PM
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No problem getting a stiff front suspension with front coil-overs.

See:
Start with:
https://forums.corral.net/forums/10768811-post4.html

Great info from MFE:
==========
The "stored energy" thing is a myth. Because the spring rates is the same, by definition both springs will compress the same amount given the same loading, so they'll both "store" the same amount of energy. However, the 14 will provide for more suspension travel before going to zero rate on extension. If your suspension unloads the spring from its perch before it's fully extended, there may be some benefit in running a longer spring. Length also becomes an issue when you factor in your desired ride height. You may not be able to get it high enough with a shorter spring or low enough with a longer one, depending on your tastes. All that said, I don't have a reco for you but those are some of the issues at hand.

EDIT: I realized after looking at formulas to explain why cutting coils increases rate, that I was wrong about stored energy. There's a formula to explain it, too:

PE = (1/2k)*(x^2)

PE is stored energy

k is spring rate

x is the deflection from neutral state (e.g., amount of compression)

Let's compare 2 springs, a 150lb/inch spring that's 14 inches long and a 400lb/inch spring that's 12 inches long.

If we apply 500 lbs of weight to each spring, the 150 will compress 3.33 inches, and the 400 will compress 1.25 inches. They'll both end up almost the exact length, at 10.7 and 10.8 inches, respectively. Think of that as "ride height"...it's about the same for both springs.


However, running through the math shows the difference

150 lb spring:
PE = (150*0.5) * (3.33^2)
PE = 75*11.111
PE = 833.3 lbs

400 lb spring:
PE = (400*0.5) * (1.25^2)
PE = 200 * 1.5625
PE - 312.5 lbs

So the longer, softer spring does store a lot more energy for any given amount of load than the shorter, stiffer spring does.

2nd EDIT: Upon further counsel, even this doesn't tell the whole story, because it doesn't account for the fact that in most cases, a spring isn't even fully extended before the strut is. In other words, it's not a matter of what the spring is capable of storing, it's a matter of how much the suspension is capable of letting it use, and that amount should be the same in both cases, and we're right back where we started
==========




Then:
https://lmr.com/products/mustang-coi...nversion-guide
====
What is the difference in spring rates and sizes? When choosing the right coil over kit for your Mustang, spring rates and spring sizes are very important and will be determined with how your car will be used. The higher the spring rate and shorter the spring, the less movement you will get from your suspension. For road racing where you do not need want a lot of body roll, you would want a smaller spring and higher spring rates. If you are drag racing, you are going to want a longer spring and a lower spring rate to allow for better weight transfer. In the middle, you will find the perfect setup for street setups. For this example we will use street driving, performance driving, road race/autocross, and drag racing.

Street Driving - LMR suggests a 12" 225lb-250lb spring setup. These kits will allow you to adjust your ride height without sacrificing ride quality.

Performance Driving - LMR suggests a 10" 275-300lb spring setup. These kits will allow you to get better performance than a normal street kit but can still be used for light track use.

Auto X & Road Race Driving - LMR suggests a 10" 350lb-400lb spring setup. These kits will perform greatly on the track for any auto x and road racing events. Ride quality will be sacrificed with these kits.

Drag Racing - LMR suggests a 12"-14" 150lb-200lb spring setup. These kits will give your drag Mustang great weight transfer for the strip. Ride quality will be sacrificed with these kits.
====


More:
https://www.stangnet.com/mustang-for...-rates.854135/

https://forums.corral.net/forums/gen...ing-rates.html


Much more:
https://www.google.com/search?q=coil...es+fox+mustang


Good Luck!

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post #7 of 17 Old 03-17-2019, 04:09 PM
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Quote:
Originally Posted by fox88 View Post
He now has the Tokico's with 12/200's and your FCA's.
It now has "Y" amount of stiffness.
It's waaaaaaaaaaaaaaaaaaay lighter than what the stock setup is.

So the confusion is, how is a 150/14, going to make the front suspension stiffer (to get "Y" back to "X") over the 12/200's he's using now?
Fwiw, assuming ~900lbs each corner in the front:
900/150 = 6
900/200 = 4.5

So, the 150 rate spring drops 1.5" more than the 900lbs spring. But, in the cases you asked about, the front end will be ~0.5" higher.



Fwiw, assuming ~1,000lbs each corner in the front:
900/150 = 6.7
900/200 = 5

So, the 150 rate spring drops 1.7" more than the 900lbs spring. But, in the cases you asked about, the front end will be ~0.3" higher.


Without knowing your corner weights, the above is a good rough estimation.
Imho, buy 2 sets of springs and see which ones you like.
LMR also has it's suggestions for an otherwise stock Stang.


Good Luck.

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post #8 of 17 Old 03-17-2019, 04:12 PM
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I really hate doing things this way. I have a 2,000 word e-mail chain with your brother. No one reading this thread has see any of that, so this is going to be confusing for them. With that said.

From reading through the e-mail, there is no complaint that the front suspension is too soft. When I asked if the front suspension ever bottomed out with the 200lbs/in front coilover springs, the response was negative. There was no complaint about the handling.

The only complaint that I can see is that the front of the car looks like it has been stepped on by an elephant when the car is parked facing downhill. That is a cosmetic problem.

Since I don't have answers to all of my questions yet, here is my best guess as to what is going on.

1) With the coilovers installed, the car is much lower in the front than it is with any other lowering spring mounted on the FCA. When the car is at stock ride height, there may be a 2.5" gap between the top of the tire and the top of the fender arch. With lowering springs installed, this gap might be 1.5". With the coilovers installed, this gap has been set to 0.5". So when the car is parked downhill, the front ride height drops 0.25". This reduces the gap to 0.25". This is a 50% reduction and the change in ride height is easily visible because of this. If the gap were 1.5" or 2.5", a 0.25" decrease in this gap would never be noticeable.

2) Because the car is so low and it has a stock k-member, the ball joint end of the FCAs is much higher than the pivot bushings of the FCAs. This means that the front suspension is at the point in its travel that there is a lot of camber gain. A very small decrease in ride height can make a large increase in the amount of negative camber in the alignment. This is related to the complaint where the car looks like it was stepped on by an elephant.

Given that the car has adjustable front struts, pushing down on the core support is not a good way to tell how stiff the suspension is. The damper adds stiffness based on the velocity that you push the car down in relation to the amount of damping that the damper has at that velocity. The damping at this velocity has zero affect on the ride height change from parking downhill because the vertical velocity of the front of the car in this case is zero.

Reduced friction in the suspension isn't going to cause any change in the ride height of the car when it is stopped. Reduced friction will result in more suspension travel when the car hits bumps.

The stock FCAs do have rubber bushings in them which add some spring rate to the front suspension as they are bonded on their ID and OD. The MM FCAs on the car do not have any spring rate added from the bushings in them. The rubber bushings affect on wheel rate is very, very small.

The stock springs have a rate which start at 425lbs/in and goes up to 530lbs/in. This results in a wheel rate which goes from 104lbs/in to 130lbs/in.

A 150lbs/in coilover spring results in a front wheel rate of 128lbs/in. This is affected by the caster and camber settings to a small degree.

A stiffer spring can be installed in the front of the car. This will result in understeer and some amount of pitching. If a stiffer rear spring were installed, it would fix these two problems. Installing a stiffer front spring will result in a reduction in rear tire forward traction.

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post #9 of 17 Old 03-18-2019, 09:17 AM Thread Starter
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The car is stock ride height, Jack. But this is the math I was looking for, just wasn't able to locate it. I will come back to this after awhile when I have time to go over the info. Thank you.

ETA: I should say, stock gap, more or less. Car has shorter tires than stock. But we will get it figured out.

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post #10 of 17 Old 03-19-2019, 12:48 PM Thread Starter
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Well, I think he's going to try the 12/250's and see how well that works. The 12/200's, in this application with those A arms that have NO resistance, just aren't strong enough to hold the front of the car in air, basically.

Seems crazy to think, but that's the case.


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post #11 of 17 Old 03-19-2019, 12:56 PM
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Quote:
Originally Posted by fox88 View Post
....just aren't strong enough to hold the front of the car in air, basically.
What????


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post #12 of 17 Old 03-19-2019, 01:11 PM Thread Starter
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What????


ks
The spring rate, is too light. I know it sounds odd. I don't understand it either. This car actually has all Baseline stuff out back!

The front of this car with those springs, has about as much resistance as a slinky. Needs a heavier spring to control the weight. I have 12/175's in my own car and it's fine, but I also still have stock A arms which have quite a bit of resistance too them. Those Maximum Motorsports arms, have really nothing and the 200's just don't play well with them. All I can tell you.

When he drives it around corners or just pulls out of a parking lot, the front end just dives to the ground, falls left or right really hard, tires up in the wheel wells. What else could it be other than too light a spring rate?

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post #13 of 17 Old 03-19-2019, 01:24 PM
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Quote:
Originally Posted by fox88 View Post
The spring rate, is too light. I know it sounds odd. I don't understand it either. This car actually has all Baseline stuff out back!

The front of this car with those springs, has about as much resistance as a slinky. Needs a heavier spring to control the weight. I have 12/175's in my own car and it's fine, but I also still have stock A arms which have quite a bit of resistance too them. Those Maximum Motorsports arms, have really nothing and the 200's just don't play well with them. All I can tell you.

When he drives it around corners or just pulls out of a parking lot, the front end just dives to the ground, falls left or right really hard, tires up in the wheel wells. What else could it be other than too light a spring rate?
I'm going to regret getting into this discussion but...

He can't have both so he must choose ONE:
1. Springs that hold the frontend up in the air for good weight transfer. (14/150 or 14/175 max)
2. Springs that are stiff so the car doesn't roll in turns and allows "spirited driving". (12/???? listen to Jack)

Which of the above does your brother want?

If he wants good weight transfer then he needs 14/150 or 14/175 BUT he could also use stiff front/rear sway bars to minimize the rolls in the corners.
In addition to the sway bars getting dbl adjustable shocks and struts allow him to change the stiffness to alter the performance/ride.

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post #14 of 17 Old 03-19-2019, 02:33 PM
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FOX88,

"The spring rate, is too light. I know it sounds odd." It isn't odd, it is impossible. Physics works, every time.

There is some information that hasn't been posted here or I haven't been given in the e-mails. If your brother finishes answering my questions, I'm sure that I would be able to figure out what the missing piece of information is and come up with a correct fix.
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post #15 of 17 Old 03-19-2019, 03:09 PM
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Quote:
Originally Posted by Jack Hidley View Post
FOX88,

"The spring rate, is too light. I know it sounds odd." It isn't odd, it is impossible. Physics works, every time.

There is some information that hasn't been posted here or I haven't been given in the e-mails. If your brother finishes answering my questions, I'm sure that I would be able to figure out what the missing piece of information is and come up with a correct fix.
Jack,
FYI, I have not spoken to anyone beyond my above post..

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post #16 of 17 Old 03-20-2019, 07:16 PM
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You can achieve the same ride height using either a longer, low rate spring or a short high rate spring , but the low rate spring is going to allow the car to drop more on weight shifts, such as braking. This seems to be the problem that Fox88 is having; air deflector hitting the ground on hard braking. That definitely sounds like a drag setup. For street use, you need stiffer springs, and stiffer dampers to go with them.

My setup:

https://goo.gl/photos/A6DML7hjefLR2Vzz6

started with 400# springs in the original kit. It was intended to work with the camber curve designed into the control arms, ON A ROAD COURSE. On the street, where you run into uneven pavement, steep driveways, and speed bumps, it just bottomed out too much. So I had to swap in 600# springs and adjustable dampers.

By the way, if a MacStrut suspension is so low that the ball joint is above the LCA pivot, it is on the positive side of the camber curve, and further compression will just increase positive camber, pulling the tire under.
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post #17 of 17 Old 03-29-2019, 10:32 AM
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Perhaps i'm lacking all the necessary info here, and i apologize for posting when i don't, but I'm running 250#/12" springs on the front of my full weight, street driven LX with the MM street bilstien struts, and stock A-arms (for now) and don't have any of the issues described here.

Ride height is fine...adjusted to approx the middle of the range. Lowest setting puts the top of tire at the fender lip.
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