Characterization of the OE Suspension Springs
 

I've just completed an analysis and writeup on the OE springs and swaybars. I'd been unable to find consistent, reliable data on them, so I eventually decided to do my own research. My goal was to estimate the "designed" spring rates as intended by Honda's engineers; that is, if we imagine (or assume) that the engineers built computer models of the suspension, what nominal spring rates did they specify? And, as a secondary question, how did they design the actual springs to achieve those rates? In this paper, I tried to answer the first question by reverse-engineering the second: I combined basic spring-rate equations with my own measurements of the OE springs' physical dimensions, and tried to rationalize those with existing published data from Honda.

As it happened, I'd been preparing a different paper (a "real" one for a "real" publication ;) ), so I figured it'd be all in good fun to use the same format. In all seriousness, though, I hope this clears up some longstanding questions about the OE suspension changes over the years.
Cheers,
John

Below are JPGs of the paper, and I've posted the PDF for download here.
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Excerpt:
“ABSTRACT
Combining publicly available manufacturer data with new measurements of original equipment (OE) springs and stabilizer bars, new results are derived which characterize the suspension springs of the Honda S2000 for all U.S. model years, including the Club Racer (CR) trim. It is shown that a total of six different OE configurations were released in the U.S., with significant variations in coil spring rates and stabilizer stiffness.

INTRODUCTION
More than a year after the end of its decade-long production run, and despite the existence of an ownership community that is unusually active in online communities, motorsport, and vehicle customization, the Honda S2000’s original equipment (OE) suspension characteristics remain sparsely documented and poorly understood. This paper attempts to partially remedy that situation by applying well-known suspension spring relations to new measurements of the S2000 OE suspension components.

The principal result of this paper is the development of new estimates of the 'designed' spring rates of the OE coil springs and stabilizer bars of U.S. model S2000s. For reasons outlined below, our estimates are indirect, i.e. based on measurements of the size and shape of the OE components, rather than of actual force versus deflection. Nevertheless, we demonstrate our measurements’ exceptional agreement with (and partial incorporation of) relevant publicly available data from Honda Motor Company. Our results identify a total of six known OE configurations and characterize the spring rates of each.”
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[Edit: Rev1, 17 Nov. 2010 - Revised values]
[Edit: Rev1a, 26 Apr. 2012 - Formatting/errata; added Table 5 (Summary Results)]
[Edit: Rev1b, Oct. 2014 - Errata]
[Edit: Jan. 2016 - PDF download link has changed; file is now hosted on Google Drive]
[Edit: Oct. 2021 - Errata; updated Google Drive link for new PDF (and fixed share/permissions settings)]

This is very cool. Having played around with both the factory parts and aftermarket, I find the factory shock dampening and the bumpstops also add a lot of rate to the suspension. Any thoughts on those?

Fantastic! Thanks for the research!

Great research. Thanks for sharing.

Cool stuff! Thanks for all the work!

Great sum up!!!

this your data formatted differently (this might be easier to read for some others as much as it is for me :) )

Summary of spring rate findings:
Front/rear lb/in
MY00-01 219/291
MY02-03 245/311
MY04-05 261/280
MY06-07 261/267
MY08-09 278/290
CR 382/339
(Note: Divide lb/in by 56 to get kg/mm.)

Summary of swaybar findings:
Model Year Spring Rate
Front/rear lb/in
'00-'01: 393/427
'02-'03: 300/396
'04-'07: 300/311
'08-'09: 354/311

'08-'09 CR: 392/362

Thanks, Croc. :thumbup: Let me also reformat it this way, to explicitly show the 6 different OE configurations.
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Bump -- added link to PDF and used reformatted data summary.

The dampers are gas-pressurized so they certainly add some amount of spring-like resistance in addition to damping. You can feel this by removing the springs and top hats and just trying to slowly compress the rod -- it takes increasing force, and the rod does "spring back". This spring force is in "parallel" with the coil spring, so it acts to increase the overall suspension spring rate. I didn't attempt to characterize this spring effect; presumably it's relatively small, and similar for all years and for front and rear, though probably not identical.

There are a host of other spring effects, most of which act in "series" with the coil springs and sway bars (and damper bodies), thus reducing the overall spring rate. These include suspension bushings, tires, and the chassis itself. The stiffer these rates, the less they reduce the overall spring rate; the tires are probably the dominant effect here (i.e. the softest spring), even though a decent rule of thumb is that their "spring rate" is on the order of 2000 lb/in.

I don't generally consider the bump stops to be part of the overall spring system since they're not designed to be used in normal operation! They're a protective mechanism, keeping the dampers from compressing out of their range and softening the shock-load forces that are transmitted to the chassis when the suspension fully compresses.

The bump stop in the s2000 is definitely part of the spring rate. It is a convoluted foam that has a progressive spring rate that is active in most high rotation turns.
I was really surprised myself went I worked on my AP2. It is similar to VW with a continuously engaged bumpstop. The density is less than celasto (Koni) but is is really long. With the weight of the car down it is in almost in contact with the shock.