Coilover Theory 101: Coil Spring Comparison
 

Hey guys,

we get asked questions about coilovers, how they work, how they are manufactured, valving theory etc etc on a daily basis, so this gave me an idea; why not make a 101 separated into several, easy-to-read parts?

If you like where I am going with this, please do let me know and what "topics" you would like me to cover, and I'll see what I can do :)

one of the questions that we get asked quite often by our customers is what is the difference between Swift Springs and the generic Taiwan springs (found on nearly all non-European coilover kits), and what makes them so much more expensive?

to answer these questions, we decided to do a comparison test, and the results are below. What you make of these results, that's for you to decide:

Side-by-side comparison - Swift 7" 10K on the left, generic Taiwan 7" 10K on the right. Notice the difference?
http://www.ycwsuspension.com/images/swiftvstw.jpg

Testing the Spring Rate accuracy on our Intercomp Spring Rate Tester, the Swift is exactly 10K:
http://www.ycwsuspension.com/images/swifttest.jpg

And for the generic Taiwan spring, it comes in at 10.25K (15lbs stiffer than rated):
http://www.ycwsuspension.com/images/twtest.jpg

Both are pre-loaded 1" then compressed 1" to get the measurements. Can you say "coil-bind"?

Some have questioned us about the accuracy of the Intercomp Spring Rate Tester, so instead here is a dyno graph of a 100lb sample Swift Spring from our Roehrig Spring Rate Tester, showing the Spring Rate (lbs/in) over an increasing compression force (lbs):
http://www.ycwsuspension.com/images/swiftdyno.jpg

For the weight test, the Swift comes in at 1.1kg:
http://www.ycwsuspension.com/images/swiftweight.jpg

And the generic Taiwan spring comes in at 1.6kg:
http://www.ycwsuspension.com/images/twweight.jpg

The conclusion from all of these tests? Not only are Swift Springs 50% lighter and extremely accurate (you ask for 10K, you get exactly 10K), they also help reduce coil-bind (i.e the coils hitting each other over large bumps). The Taiwan spring? Maybe after 6 months of driving, it will finally be 10K, then 6 months later, 9K!

I've deliberately made this post short and sweet, so as to encourage questions, so if you have any, please feel free to ask!

Not "coilovers theory 101" but more thinly disguised advertising 101.
Test completed ith a sample size of one for only two products with nothing to be learned for the "data".

Advertising? Far from it.


I'm just posting up the results from a simple quick test done so far, and will post up more data on different springs, different brands etc


Tell me what sort of test you want to see, and I'll see what I can do.


P.S If you have nothing to "learn" from this data, that's fair enough. But I'm sure a lot of people in the community appreciate the data being shared, and I'm open to suggestions

To be truly sientific we will need the calibration dates on your test equipment. Also test at least 4 seperate parts made a different times to verify quality. Then you will need to use them for a while and pull off and retest.

I will try to get the calibration data from Swift. For our own tester, I will need to check with the Intercomp documents that came with it.


Regarding testing 4 separate parts, that is easy to do. Unfortunately, Swift test every single individual spring after it comes off production to make sure the rate is 100% accurate (that is why they have an expensive Roehrig spring tester); if it does not meet the specified rate, the spring is simply scrapped. Therefore, it is nearly impossible to find a Swift spring that is not at it's advertised rate when new.


However, testing them after being used for a few months, that is something that we can and will do. Whether this thread is updated with the data or not though, that is up to the community to decide.


I am not doing this to advertise any particular brand or company (contrary to my username), so if people deem this as "advertising in disguise", then I won't continue.

Need All the other spring companies now.

Keep them at a single rate. (Or as close if the company only deals in lb)

Eibach, Hyper, ect.

I am joking. I have no doubt the swift springs are superior. My opinion on buying is that you may not want to buy the most expensive one out there, but you do not want the cheapest!

What does 10K mean?

+1 on this,,, how does 10K equate to 5xx on the test rig?

Right? I was hoping to get there. Not as a gotcha or anything, mind you. Discussion is free and interesting.

10 Kilogram/millimeter = 559.974147 pound force/inch

So, actually the swift springs are not exactly 10k.

557 pound force/inch = 9.946888 Kilogram/millimeter

Yes, it's borderline pedantry to argue about, but one could assert that if they wanted to claim it was "exact", it'd be within 1 pound force/inch... So 559 or 560, certainly not 557.

Honestly, with a spring, I'd be more concerned about the standard deviation. And that speaks to earlier posts in this thread about testing a bunch of Sprint's springs. They certainly are not all exactly the same, that is statistically impossible given metallurgical and manufacturing variance. With a test across several springs of the same spec, we could establish if the STD is within a reasonable % - and that would speak to the overall quality of Swift in some objective manner.

The same test should be done with Taiwan brand x and y. Then we can compare STD across brands for an even more informed opinion.

If you wanted to extend the test, you'd also include some simulated mileage on a dyno and then retest to see how stable the metallurgy of the springs is: 1) how much has their rate changed over time 2) what is the STD on that change across springs.

Could be very fascinating and revealing data.

Thanks for sharing this information .. but it really wasn't coilover theory 101 ...
was more like brand vs generic 101.


Typically brands are held to a higher in-house standard than generics and we see this in your sample size of 1 test. ¯\_(ツ)_/¯

I like the idea of characterizing variability. For the folks that do not end up getting a corner balance after alignment at least knowing that the spring rates from side to side are close helps a bit if one is careful with setting up the spring perch on the damper body.

How the spring rate changes over some period of use would also be useful.

The funny thing is, right after I took that picture, the value changed up to 558lb's! lol. It was fluctuating between 557 and 558, but it was only 1-2lbs, so I decided to just leave it.

We have thousands of springs sitting here on our shelf, so yes, we will be testing various brands, rates, as well as ones that have varying degrees of mileage. Infact, testing on a new spring isn't really the best judge of the quality of a spring, as both springs in this simple test that I done actually fell within Swift's own 3% variation (Eibach's is 5%). What will determine the quality is what each spring will be like after say 6 months, 12 months etc. That is coming :)

Regarding the generic Taiwan spring, not a lot of people realise this, but there is actually only 1 spring factory in Taiwan that supplies the entire aftermarket coilover market in Taiwan. Well, that's a lie, there are a couple more but quantities are so small it's insignificant. All the established brands go through the same factory for springs (whether it's BC, D2, STD, Yellow etc) So whether you purchase from a trading company or even another "spring factory", the generic coilover spring is going to be from the same initial source.