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I've always wondered how a progressive rate spring was rated. If you have a progressive spring that is rated at 250 lb/in, is that 250 at the FIRST inch, or the MIDDLE inch? Is there a standard?
^If it's progressive and they only quote one number, then you'd have to ask the manufacturer (or -- natch -- measure them yourself!). I'm not aware of any standard.
The way a progressive spring works is by designing one or more coils to fully compress under moderate load, thus becoming inactive. With fewer active coils, any further weight transfer "sees" a higher spring rate.
Once mounted and preloaded, the OE springs appear to be designed for linear operation throughout the suspension's range of motion; however, the bump-stop foam provides a progressive characteristic (and engages at relatively moderate loads). All years and models use the same bump stop foam (same two part #s, one for front and one for rear) so characterizing a couple parts should be sufficient.
I thought the S2000 did have progressive springs. I also thought most aftermarket springs were progressive rate. I see that Eibach's description of their Pro-Kit springs includes "Progressive Spring Design for Excellent Ride Quality". Their page doesn't mention rates though.
I recently installed threaded sleeves and spring perches for my Konis, and installed straight raight coilover springs on them. Since the OEM dust covers wouldn't fit inside the 2.25" springs, I was able to see how much compression travel was remaining after preloading the suspension. Even after lowering the ride height by 3/4" in the front and 1" in the rear, there's still at least an inch of compression travel before the bump stop comes into play. Since the "motion ratio" is somewhere around 2:1, that means that I'd have to load it up enough to compress the car about 2 more inches before the bump stops would touch. At stock ride height, that would be about 3 inches. Do you think that happens from anything other than bumps?
I've also seen articles quoting Honda as saying that the S2000 has progressive spring *rates*, but I can only assume this refers to the bump stop foam. By and large, the springs themselves appear to behave linearly. (A couple of the springs I examined showed very minor signs of coil-bottoming, enough to have caused up to about 1/8 of a coil becoming inactive; this likely happened only over the worst bumps.)
As for where the bump stops engage, couple observations:
- The motion ratio is actually about 0.7 (spring rate goes as MR^2, that's where you get the 0.5 factor).
- Reference [5] in my paper gives the full jounce travel for stock AP1 as about 2.4in. front and rear (plus 1.9in full rebound F, 2.2in R). Not sure if that's at the damper or wheel ("should" be at the wheel, but you never know)...Either way it seems low for an absolute limit, so perhaps that's the bogey value we're looking for: the point where the bump stop foam begins to engage. I'd like to see someone here actually measure this on their own.
Regardless, I'm certain that with R-compound tires, you can push a car well into its bump foam, even with 600lb springs:
Edit: P.S. Let's not forget that lowering a car changes its roll-couple (CG height minus roll axis height), which can dramatically increase lateral weight transfer during cornering (undoubtedly the case in photo above).
Originally Posted by robinson,Jan 20 2011, 05:42 PM
I had 800 lbs springs in front w/32mm sway and I have a rub mark on the underside of the fender, on street tires.
But that can just be over bumps, I'm curious to know what it's at in a corner. Plus it all depends on how low you are, the lower you go the stiffer you need the springs to be.
I'm guessing the only real way is with a camera or some expensive telemetry data acquisition stuff which I don't have yet.
I guess I'm not getting what "Motion Ratio" means. I meant to say that the wheels seem to move about twice as much as the shock. That's how I guesstimated my numbers.
If you want to see how much the bump stops are being used, go to a smooth parking lot, jack the car up, smear some of that dark blue dye that you use for ring and pinion swaps on the top of the shock absorber, then do some figure 8's. If there's blue dye 1/2" up the bump stop afterwards ... you've got your answer.
01-20-2011, 11:37 AM
I just need to figure out where to put it.