Spring Stiffness Spreadsheet

[derieuz]

Was very picky about picking springs for my car, so I thought this may be of help to some people who are fine-tuning their suspension and want a spring that will make them happy.

If there is any errors with this data, please let me know!

OEM GT Rates: Front: 160 lbs/in, Rear: 668 lbs/in
Performance Pack Rates: Front: 165 lbs/in, Rear: 728 lbs/in

All Values are compared to OEM GT Rates at the moment!

BMR Street:
1.25 Front, 1" Rear (Drops, Linear Spring)
6.25% Stiffer front
10.78% Stiffer Rear

BMR Drag:
1.25 Front, 1" Rear (Drops, Linear Spring)
6.25% Looser Front
19.76% Stiffer Rear

BMR Track:
1.25 Front, 1" Rear (Drops, Linear Spring)
87.5% Stiffer Front
26.49% Stiffer Rear

Eibach Pro-Kit:
1.1" Front, 1" Rear (Drops, Progressive Spring)
25% - 96.25% Stiffer Front
19.76% - 36.83% Stiffer Rear

Eibach Sportline:
1.5" Front, 1.3" Rear (Drops, Progressive Spring)
35.63% - 106.88% Stiffer Front
31.59% - 48.8% Stiffer Rear

Eibach Sportline Front with Pro-Kit Rear:
1.5" Front, 1" Rear (Drops, Progressive Spring)
35.63% - 106.88% Stiffer Front
19.76% - 36.83% Stiffer Rear

Steeda Sport Springs:
1" Front, 1" Rear (Drops, Unknown Spring, I believe it is linear.)
28.9% Stiffer Front (OEM) 25% Stiffer Front (PP)
36.2% Stiffer Rear (OEM) 25% Stiffer Rear (PP)

H & R Sport Springs:
1.1" Front, 1.3" Rear (Drops, Progressive Spring)
?% Stiffer Front
?% Stiffer Rear

Ford Racing Springs:
1" Front, 1" Rear (Drops, Progressive Spring)
?% Stiffer Front
?% Stiffer Rear

Vogtland Sport Springs:
1" Front, 1" Rear (Drops, Progressive Spring)
?% Stiffer Front
?% Stiffer Rear

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[cbrtrx]

Lots are cool info but and I hate to throw a curve ball in your specs but all the manufactures rate their springs differently so those numbers really mean very little compared to each other. Some are just static rates not even in their working range when on the car. Just because a spring has a progressive static rate does not mean it wouldn't be close to linear when installed.

 

[Todd15Fastback]

Steeda confirmed with me, their spring is 25% stiffer than the PP springs.

 

[derieuz]

Lots are cool info but and I hate to throw a curve ball in your specs but all the manufactures rate their springs differently so those numbers really mean very little compared to each other. Some are just static rates not even in their working range when on the car. Just because a spring has a progressive static rate does not mean it wouldn't be close to linear when installed.

I did not know this, and I do not know much of the technical functions of springs, but the data I do have is from the tech specs provided by the manufacturers, and they do use the same numbers as I used to compare their rates, for example the BMR handling spring was said to be a 300 lbs/in spring in the front compared to the OEM 160 lbs/ft, so that's how I calculated all of those percentages

 

[cbrtrx]

Steeda confirmed with me, their spring is 25% stiffer than the PP springs.

Its easy to "confirm" anything, how was it tested? Who tested it? To what regulations?.... Any manufacture can post any claim, way too many variables.

Do you see what I'm getting at?

 

[Sixth]

you should put H&R super sports too and arent the pp springs lower than the non pp cars?

 

[VTECSAUCE]

I did not know this, and I do not know much of the technical functions of springs, but the data I do have is from the tech specs provided by the manufacturers, and they do use the same numbers as I used to compare their rates, for example the BMR handling spring was said to be a 300 lbs/in spring in the front compared to the OEM 160 lbs/ft, so that's how I calculated all of those percentages

cbrtrx has a point, variable spring rates are very difficult to gauge as they essentially have more than one spring rate built into the same spring. They aren't desirable for performance, particularly racing as the handling can be unpredictable near its limits. They are useful for lowering springs as it can lower the car and leave a somewhat soft spring rate for comfort but if you were to hit a bump hard enough the stiffer rate would essentially be there as a safety to prevent damage at the expense of comfort if the travel of the shock/strut were to go far enough to bypass the more loosely wound, softer part of the spring. This is what I took from articles I've read comparing linear to variable spring rates, hopefully I'm not too far off. Perhaps cbrtrx can verify that. Regardless I appreciate the time you took to look up these numbers and I'd like to see it updated perhaps when some coilovers and more suspensions come out.

 

[derieuz]

cbrtrx has a point, variable spring rates are very difficult to gauge as they essentially have more than one spring rate built into the same spring. They aren't desirable for performance, particularly racing as the handling can be unpredictable near its limits. They are useful for lowering springs as it can lower the car and leave a somewhat soft spring rate for comfort but if you were to hit a bump hard enough the stiffer rate would essentially be there as a safety to prevent damage at the expense of comfort if the travel of the shock/strut were to go far enough to bypass the more loosely wound, softer part of the spring. This is what I took from articles I've read comparing linear to variable spring rates, hopefully I'm not too far off. Perhaps cbrtrx can verify that. Regardless I appreciate the time you took to look up these numbers and I'd like to see it updated perhaps when some coilovers and more suspensions come out.

If I recall, isn't a progressive rate spring better for the daily driver who wants to track the car once in awhile? You get the benefit of the lower rates when not pushing the car, and then as you corner harder and push it further (loading the springs more) you feel the higher rates of spring? Thats what I've always thought, the more you load up the car the stiffer the rate from the progressive spring

 

[derieuz]

http://automotivethinker.com/suspension/linear-vs-progressive-rate-springs/

Linear springs are more predictable, and have the same rate across the whole travel, so if a spring is rated at 100 pounds per inch, every inch the spring compresses will take an additional 100 pounds of force. For a progressive spring, it is not consistent and difficult to gauge (like stated above), depending on how the coils are arranged, it could have 3 inches of travel rated at the lower rate and then once the lower rate springs are fully compressed, the higher rates will kick in. The also you can begin to compress the higher rate portions of the spring while loading up the lower rate portions depending on the rates

In the short, linear springs will give you a harsher ride as they will always be stiffer but they are far more predictable while a progressive spring will give you the stiffness when you are loading the spring up and give you a less harsh ride when you are just hitting bumps, the downside to progressive rates is predictability for performance drivers based on the stiffness. Considering all of the above progressive rate springs start out stiffer than our cars, it's safe to say that they still will be just as predictable or more predictable than our OEM springs.

 

[BMR Tech]

When we tested the OEM springs from our PP, we test them in house and we also verify the results with Betts Spring, one of our coil spring suppliers.

To my knowledge, we are a little different than many of the big spring suppliers. We design our springs 100% in house, then have them built to our specs. After we spec out several designs, we then test them on our cars, and others as well.

What cbrtrx is saying above, is correct about how we all rate the springs, test them, etc. For example, if you take a free height front spring that is 13" tall, you don't test the spring from 0" to 6" compression like I see many people do. If the compressed (ride height) spring is at 9"....then we will start our testing from about 10" compression, and go down from there.

Of course, a progressive rate spring is different, because it will get stiffer as you compress it. But when you see a rate on a spring of like 120-310....that 120 is usually irrelevant. For that particular spring, you would want to test it at it's compressed height when installed, then compress further. So, if it were ME...then my rate for that spring would be more like 220-320. (just guessing at those #'s)

Then you have a dual rate spring. This is a spring that has a linear working rate, when you drive the car....but the "initial" rate would be compressing the dead coils. So, you can have a 110-200 dual rate spring...but the linear working rate would be 200. There would not really be a point in even mentioning the 110lb rate, because that rate is taken up when the spring in in compression upon installation.

You can call that softer rate of a dual rate spring, a helper section, tender section, or simply "dead coils". When you see a spring that has several coils that stack, then those coils are typically just used to take up space to ensure the spring has a free height similar to OEM, and that the spring will not fall out of the spring pocket when the suspension droops.

So anyways, our front springs for the S550 are a linear design. The rear rates, we are testing dual rate coil designs, as well as linear.

The rates we advertise, will be the working rates that you experience while you are using your vehicle.

 

[908ssp]

If you're serious about pushing your car stay away from progressive rate springs they can get you in trouble. They also don't really deliver what they promise any time you hit a really big bump. The only time they work is for slow driving a seriously lowered car all looks no performance. You can significantly increase spring rate but you have to have the appropriate shocks. It isn't compression that is the problem it is rebound. With more spring rate on standard shocks the car will return too quickly which in turn upsets the car. Springs need to be properly controlled and that is what shocks do.

 

[BMR Tech]

^ I was just about to say that.

Personally, I am not a fan of progressive rate springs, for anything other than running errands.

 

[carguy]

I thought the Pro Kit is linear??? I know your right about the Sportline kit being progressive, but I'm pretty sure the Pro Kit is linear. I could be wrong...

 

[2Cool]

I thought the Pro Kit is linear??? I know your right about the Sportline kit being progressive, but I'm pretty sure the Pro Kit is linear. I could be wrong...

http://eibach.com/america/en/performance-suspension/performance-springs/pro-kit

Nope, progressive. I got them as they are a good compromise on reasonable drop, daily comfort, and occasional fun in the twisties.

 

[carguy]

http://eibach.com/america/en/performance-suspension/performance-springs/pro-kit

Nope, progressive. I got them as they are a good compromise on reasonable drop, daily comfort, and occasional fun in the twisties.

Wow, I guess I thought just based on how the coils looked compared to the Sportline. They "look" like linear rate as they don't have the tight coil section on one end of the spring like the Sportlines do.

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