Rates of some ebay 'no-name' springs
 

Out of curiosity, I picked up these springs yesterday:

https://www.miataturbo.net/miata-par...and-new-70991/

They are you're basic no-name special that come with threaded sleeves for more rate and adjustable ride height. Free length is about 7".

https://www.miataturbo.net/attachmen...ine=1360961428

I have almost never seen hard data about how or why they suck, although everybody asserts that they do.

Here you go, the rates of all four on a professional test rig.

https://www.miataturbo.net/attachmen...ine=1360961428

I tested 2 inches of travel from a ~100lb preload base -- a pretty standard procedure. I didn't do lots of back-to-back runs, but even cheap coil springs tend to have repeatable performance.

Who knows what the nominal rate is. 550 lb/in maybe? They are all within 2.5% of that, which is not completely awful. I would take 3% error for a street car.

Who knows what they expect you to do front/rear. 550 all around is pretty much a non-starter. I would run 1 & 3 on a race car though, if I was targeting 550.

cheers

donour

Very cool. Thanks for the info.

Not too shabby for the price. We're using the threaded collars on POS track miata, they're doing great. I'm not too surprised they're decent. I bet these are the QC failures out of the china shops that make the "real" springs.

In case you haven't seen this yet:
FCM_MSDS_TUTORIAL.xls

Now get to building my coilovers! :D

Yeah. They are a fine part. It looks basically like an eibach with no logo. If you told me they were 545 and 555 lb springs, I would say they are exceptional quality.

I don't even want them really. I was just curious what the ebay guys were selling. Now that they have rate plots, they actually are valuable. PM if you have a use. If they hang around my office, I'll end up giving them away.

donour

From the book Chassis Engineering by Herb Adams:

The formula for figuring spring rates without a test rig is:

Gd^4/8ND^3

G = Torsional modules for steel = 11.25 x 10^6 = 11,250,000
d = Wire diameter in inches
N = Number of active coils
D = Mean coil diameter in inches
8 = A constant for all coil springs

The G factor in the equation is always the same for coil springs made of steel. The coil wire diameter (d) can be measured with a caliper. It will be the same for the whole length of the spring unless it is a spring of variable rate, in which case you can't put a number on it anyway. For our example, we will assume a wire diameter of .62 inches.

Determining the number of active coils needs some judgement on your part. The key word here is active. If the ends of the spring are flattened or ground, these coils are not active, since they are resting on their mounting pads. When counting active coils, only consider those that can move as the spring is compressed. For our example, we will assume a spring with 10 active coils.

Determining the mean coil diameter can be done with a tape measure. [We want the diameter from middle of coil thickness to middle of coil thickness. Measuring from outside to outside then subtracting the measured thickness of the coil wire will accurately give you a center to center] For the example, assume a mean coil diameter of 5.00 inches. Filling in the formula with the measured [example] numbers will result in:

coil spring rate = 11,250,000 x .62 x .62 x .62 x .62 / 8 x 10 x 5.0 x 5.0 x 5.0

or

coil spring rate = 1,662,337 / 10,000 = 166 lbs-in.


Several things should be noted from this calculation.

1. If we cut one coil from the spring it will have less active coils, its length will change and the rate will go up.

coil spring rate = 11,250 x .62 x .62 x .62 x .62 / 8 x 9 x 5.0 x 5.0 x 5.0

coil spring rate = 1,662,337 / 9,000 = 187 lbs-in.

That is about an 11% increase or proportionate to the amount cut from the spring.


2. Increasing the wire diameter will cause a dramatic increase in the rate of the spring. If we increased the wire diameter only 1/32 of an inch [.03] the rate would be [edited calculation out] = 223 lbs-in.


3. Nothing int he spring rate calculation indicates that a coil spring ever has a change in its rate. The rate is determined by the material, spring steel in this case, and the dimensions of the spring. Coil springs don't wear out or lose their rate.


4. Nothing in the spring rate calculation describes spring load. Spring load determines how much weight a spring can support at a given height. The spring rate only tells how much the height will change as the load is changed. A spring can lose its load rating over time or if the steel is not heat treated properly. However, when a spring sags, its rate is still the same as when it was new.

I have the silver ones from jessiekits on ebay. I figured they were 525-550 based on the online calculators. 2 for the front and a pair of 350's for the rear.

You plan on running 550/550 setup all around?

well how does a real brand spring compare?

how many sets do you think you'd have to buy before you could sell matched sets?

I'm running Ebay 550 front and QA1 350 rear (Eibach 325 on the rear of the track car)

Talking about the OP seeing that he has 4 of the same rate.

No, he's not planning on running that rate at all four corners. Just needed a few for comparison.

*Answering for Donour since he's busy prepping for Daytona 500.

I could run a 550lb spring in the rear, lol.

Regarding spring testing (from Dennis Grant's Far North Racing site):

While we're on the topic of "picking springs", I am of the opinion that there is only one spring provider worth a damn - Hypercoil. Of all the springs I have tested - you need a spring tester, MK Technologies makes a good one (and Hoosier Tom will sell it to you) - the only springs that reliably tested in spec were the Hypercoils. The worst offenders were the no-name purple springs that come on JICs; I saw 25% variation on some of these.

Just like shocks you must test your springs, and do so regularly. The spec on a Hypercoil is 3%, and at stiffer rates, it is possible to try and add 50lbs of rate, but swap in a spring on the soft side of the spec for a spring on the stiff side of the spec, and effectively do nothing except fool yourself. TEST TEST TEST! Unlike shocks, no spring vendor is going to provide test results for individual springs, so you get to buy a spring tester. Tell Marty and Tom I said "Hi".

So the rates can be lived by, how about sagging and the rates after they have had about 10k miles to sag?

Correct-a-mundo. I probably won't run that rate at all on the miata. I certainly wouldn't run it at all four corners.

I suppose it depends on how picky you are about 'matched'. A difference in 5-10 lbs @ 550 is within the margin for basically any setup you'll see.

There are people who have a reason to care about that last 1%, but in that case they need a specific target (e.g. 445 lbs, not 550). You would have to buy a lot to have a >50% chance of getting two at such a target. Assuming they are uniformly distributed over a twenty lb range, you need forty (less for a normal distribution). That basically only happens a the highest level of motorsport.

There are places you can go to spec a spring, but it is expensive -- often over $1k per spring for an exotic one.

Honestly, we don't know until somebody tries. Because I ran them through basically their whole range on the tester, I kind of expected them to sag/yield immediately. They didn't. It will partly depend on how they are treated. For example if you constantly coilbind, the spring won't last as long.

donour

I suspect that the majority of common 2.5" springs all come from the same couple factories in China. Now, if a company is winding their springs in the US then they might be sourcing steel from US companies. I know for a fact that US factories can produce a better grade wire steel but that comes at a higher price. I also know that in some US factories they sample the steel and view the grain structure under a microscope to make sure it's good.

Thanks Donour! Good to know. I was also curious about these rates. I guessed them to be 450-500 comparing the thickness of the coils to my Summit Racing 450s.

I have been running a similar set (blue) that I measured to be close to 550lb (using car scales and a jack). They work great in the front and with collars and two spare springs worked out cheaper than a single spring from the big guys.

On the steel production topic.

It is interesting that the new reactor vessels needed for the firs new nuclear plants in the US can no longer be made in US, but are coming from Korea, because we no longer have the expertise or the ability to deal with these large forgings.

It's just sad that we are not as awesome as we used to be.

Another set of ebay springs came across my desk this week, so I rated those too.

These are from one of the lowest priced kits : Front Rear Aluminum Scaled coilover 0 3" Spring Kit 90 97 Miata MX 5 MX5 NA Blue | eBay

Unlike the last set, the front and rear are different. However, at first glance I didn't think they were because the wire size is pretty close and there are absolutely no labels. It wasn't until I got them on the rater that I realized the wire diameter is different front/rear.

F: 2.5" ID 5.5" FL, 11.3mm wire gauge
R: 2.5" ID 5.75" FL, 10.2mm wire gauge

It would be very easy to swap a front/rear if you're not paying close attention.

My only other comment would be that they are pretty short. Too short?

https://www.miataturbo.net/attachmen...ine=1384101118

https://www.miataturbo.net/attachmen...ine=1384101118

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donour