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Old 11-19-2007, 11:49 AM   #1
Scooby921
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Default Spring Stiffness Comparison - Chart/Data

Updated

Data file and stiffness plots are attachments at the bottom of this post. Enjoy and look for updates as I test more springs.

For those who haven't seen this before...

Awhile ago I started using some of the wonderful test equipment I have here at work to test the different coilover springs I've been putting on my car. As a benefit to the community I decided to post the results here for everyone to see.

Along the way I've had some discussions with Clint @ TiC, Colin @ Swift Springs, some engineer at Hyperco, Brian @ Vorshlag, and our wonderful moderator ButtDyno (John). Initial testing was done at my own discretion and to loads and calculation points that I decided were good enough. While talking with Swift they mentioned that the industry standard was to test the spring to its maximum "useable" stroke and calculate stiffness between 30% and 70% of that distance. While looking over Eibach's website I see that they use 20% to 70% of the "useable" stroke to find stiffness, contraditcing Swifts claim of an industry standard. To further remove any sense of an industry standard, Hyperco noted that they load each spring to a predetermine preload (which wasn't given to me) and then compress the spring 1 inch and take a data point. Then compress another inch and take a data point. They'll take as many data points as the spring allows and calculate the rate through those points.

After some deliberation we determined that Hyperco's method makes the most sense. Not for volume of data or averaging points, but because they use a data point that is useful to most people. The springs are tested from 0 mm to 100 mm of displacement (machine limit, unless the "useable" stroke is less than 100 mm). Stiffness calculations are performed between the predetermined preload and 25 mm of compression. This was chosen to represent the displacement and stiffness through which most daily driving events occur. With the majority of race tracks being smoother than normal roads I expect that most of those inputs fall in this range of compression as well.

For those who may be wondering, there is a difference between maximum stroke and the maximum "useable" stroke. "Useable" stroke is the amount of travel in the spring before the coils begin to contact and the spring rate starts to increase.

For now the testing setup can only support linear, grounded, coilover springs. I have plans to develop a fixture capable of supporting OEM style springs, but need to find time and funds to get something built before I can begin testing. If you have some coilover springs that you'd like to have tested and rates verified, shoot me a PM and we can work something out. I'm personally interested in testing springs off some of the more popular coilovers that the community is purchasing these days (Megan, Buddy Club, Tein, KW, RCE, etc).

Here are some pictures of the current setup. Pictured is one of ButtDyno's springs from Hyperco / Hypercoil.


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Attached Files
File Type: pdf Coilover Spring Comparison.pdf (11.5 KB, 154 views)
File Type: pdf New Coilover Spring Comparison - Chart.pdf (42.5 KB, 168 views)

Last edited by Scooby921; 04-15-2008 at 09:56 AM. Reason: Updated data and chart...using my special "supporter" allowances to post an attachment :banana:
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Old 11-19-2007, 03:46 PM   #2
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to which Scooby921 and I have been talking. If you have a set of blown stock struts with unmolested perches please contact us as we'd like to buy them to build the test rig.
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Old 11-20-2007, 07:34 AM   #3
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Scooby921, it looks like all the springs are fairly linear and true to their rate unless the differences are a bit too small to show up in the chart. (And if they are, then that's good, right?)

Quote:
Originally Posted by Turn in Concepts View Post
to which Scooby921 and I have been talking. If you have a set of blown stock struts with unmolested perches please contact us as we'd like to buy them to build the test rig.
I can donate a rear 2005 STI strut housing.
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Old 11-20-2007, 09:24 AM   #4
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Nice to have objective data. I live in your same town and can offer the following springs for test:
  1. OE wagon springs
  2. STI wagon pinks
  3. Prodrive 02-03 blues
  4. RCE wagon springs
  5. Some mysterious purple sedan lowering springs (Tanabe?)
When measuring OE springs, it'd be nice to measure the check load to determine the trim height. It'll also be nice to see where the non-linearity occurs with the coil-on-coil progressive springs so we can debunk the myth that the spring makers use progressivity for anything other than maintaining spring seat contact at full rebound. I imagine measuring side-load-compensation forces would be too much to expect but would be great to have.
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Old 11-20-2007, 11:32 AM   #5
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Quote:
Originally Posted by stretchsje View Post
Scooby921, it looks like all the springs are fairly linear and true to their rate unless the differences are a bit too small to show up in the chart. (And if they are, then that's good, right?)


I can donate a rear 2005 STI strut housing.
Yeah. I dropped linear fit curves on there to check. R^2 value for each was 0.9997...pretty linear. I'm just interested to see if some of the cheaper coilovers use cheap springs that aren't as linear as they should be. Maybe it would be more useful to have the R^2 value for each spring's linear fit curve instead of the % difference.

OK, so we have a strut housing / spring perch to use. I'm pretty sure I have front and rear topmounts from my '05 in the garage. I guess I just need a rear topmount from a bugeye to complete the fixtures. I'm really excited to see the difference in progressive rates and inflection points for the OEM style springs. I just hope the assembled fixtures are short enough to fit under the test machine.

Last edited by Scooby921; 11-20-2007 at 11:49 AM.
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Old 11-29-2007, 04:04 AM   #6
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I have a set of bugeye rear top mount to loan you.
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Old 11-30-2007, 01:03 AM   #7
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Quote:
Originally Posted by Turn in Concepts View Post
to which Scooby921 and I have been talking. If you have a set of blown stock struts with unmolested perches please contact us as we'd like to buy them to build the test rig.
i have a friend who may be able to give you a set of blown rears... i'm going to link him to this post.

btw your fender braces are awesome, i recommend them to everyone now.
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Old 02-11-2008, 03:56 PM   #8
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Finally got around to testing the HKS springs. They are linear just like Eibach and Swift, but they are the furthest from their claimed spring rates.
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Old 02-11-2008, 05:55 PM   #9
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Hyperco OBD would be a good one to throw in there... their new springs are cheaper than the Swifts and have very similar specs. If I have enough time to ship them to you before I have to install them, I will.

john
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Old 02-12-2008, 09:20 AM   #10
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Quote:
Originally Posted by ButtDyno View Post
Hyperco OBD would be a good one to throw in there... their new springs are cheaper than the Swifts and have very similar specs. If I have enough time to ship them to you before I have to install them, I will.

john
When do you plan on installing them? The test stand I've been using for testing will be tied up for the next month or two with durability testing of some engine mounts.
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Old 02-12-2008, 09:22 AM   #11
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Well our first event is April 6th so they'll need to be on the car before then. I'll wait as long as I can

john
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Old 02-12-2008, 09:53 AM   #12
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I checked the test schedule again. That machine is only tied up through March 4th. If you send them around that time I can have 'em tested and back to you within a week.
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Old 02-12-2008, 11:43 AM   #13
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nice work- funny I missed this thread the first time around

if you ever get it rigged for oe style springs that would certainly be useful for a bunch of folks
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Old 02-13-2008, 02:27 AM   #14
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Nice work! can't wait to see this chart grow. it will be nice to see some of the proprietary spring rate springs get debunked.
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Old 02-13-2008, 02:49 AM   #15
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nice nice!! moaar springs pls.
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Old 02-13-2008, 09:30 AM   #16
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Still gathering topmounts and a strut body / lower perch so I can build a test fixture and start testing OEM style springs.
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Old 02-13-2008, 10:23 AM   #17
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^^you rock!
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Old 02-13-2008, 02:00 PM   #18
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Quote:
Originally Posted by Blue5spdWRXWgn View Post
Nice to have objective data. I live in your same town and can offer the following springs for test:
  1. OE wagon springs
  2. STI wagon pinks
  3. Prodrive 02-03 blues
  4. RCE wagon springs
  5. Some mysterious purple sedan lowering springs (Tanabe?)
When measuring OE springs, it'd be nice to measure the check load to determine the trim height. It'll also be nice to see where the non-linearity occurs with the coil-on-coil progressive springs so we can debunk the myth that the spring makers use progressivity for anything other than maintaining spring seat contact at full rebound. I imagine measuring side-load-compensation forces would be too much to expect but would be great to have.
YES... please test these and post the results.
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Old 02-13-2008, 02:10 PM   #19
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http://spreadsheets.google.com/pub?k...eL_KhwEw&gid=1

I can't see it (google docs blocked at work) but I bet there are plenty in there we don't have rates for. IIRC the Cobbs are one...
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Old 02-13-2008, 02:19 PM   #20
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it would also be interesting to see how close the rates actually are for those companies that post them

a buddy a long time ago tested the first Prodrive WRX springs- obviously they are not posting their rates
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Old 02-13-2008, 04:12 PM   #21
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Well, I think I just found my strut body to hack up. Assuming it has topmounts attached...I'll have rears off of a bugeye outback sport. I'm assuming those are standard '02-'03 rears. If I can find my old topmounts in the garage I should have '04+ rears and fronts ready to go.

Anyone have a 6"x6"x1/2" steel plate they want to donate for the base of the test fixture? If you can machine it ahead of time, I'll need a hold bored in the center (whatever the diameter of a strut housing is about an inch below the perch).
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Old 02-13-2008, 05:05 PM   #22
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do you have any need for a usdm 04 sti spring set to test?
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Old 02-14-2008, 09:16 AM   #23
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Quote:
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do you have any need for a usdm 04 sti spring set to test?
Possibly. I'm going to start with whatever the locals have lying around. There are enough STi's here that we might not have to worry about shipping a set of those back and forth. Nonetheless, if people can start putting up a list of what they might have lying around the garage I can at least get started with a testing plan.
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Old 02-14-2008, 02:33 PM   #24
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well let me know. i have a set with about 35k miles on them sitting in my garage.
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Old 03-06-2008, 10:09 AM   #25
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So I haven't gotten any further along with this because I'm still need to piece together my testing fixture for OEM springs. We've also been busy running durability tests that take several weeks and I haven't exactly been able to steal time on that particular test machine.

Anywhoo...my newest set of toys showed up in the mail yesterday. These will be tested individually and as pairs before they go on the car.
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