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As I'm waiting for parts (upper mount/bearing) to install my GAZ adjustable front struts, I decided to figure out a method to directly measure the spring rate of the OEM springs.

After mocking up a more complicated lever contraption involving a floor jack, aluminum "2x4" beam and a bathroom scale, I took a look at my drill press and was struck with inspiration! :) All I did was put my digital bathroom scale on a scrap of 2x12 on the drill press table, added a scrap of plywood to the GLASS scale surface and used the drill press' built-in table height adjustment to create the right spacing for the several springs I had on hand. I took measurements by zeroing the scale, then cranked the drill press down exactly 1" in a series of 3 reading per spring.

Here are my results:

300 lb/in springs provided by GAZ: 276lb/in
OEM Insight springs (front): 81.3 lb/in (avg of 82, 78, 84)
OEM Insight springs (rear): 76.5 lb/in (avg of 75.5, 77. 77)
OEM Chevy Aveo springs (rear) (cut down a coil or so): 111.8 lb/in (avg of 109.5, 112.5, 112.5)
OEM 2010 Honda Fit springs (rear): 110.3 lb/in (avg of 109, 112.5, 109.5)

Caveat: Obviously a bathroom scale isn't the most accurate scale in the world and my methodology is a bit crude but I think you can safely take away from this some relative stiffness ratings.

I'm REAL curious how the car feels with springs 3.4x the stiffness up front than it came with. Considering Ground Control ship their kit with 425 lb/in springs, I cannot believe that spring rate w/OEM dampers even remotely works.
 

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I like your style :)

Interesting the fit spring is so close to the insight one. With 30% more body weight and almost 3x the carrying capacity I would have thought the rate would be doubled.

Edit: who's, I was looking at the Daewoo numbers. Still not s much as I would have thought though.
 

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Good for you. These measurements are likely much better than you give them credit. The bathroom scale is probably pretty accurate at these low pressures... Still surprised at how soft the stock front springs are. And surprised that Ground Control's Insight kit comes with 425 lb/in springs (front at least). Is that right??

JoelR, you're the one with the spherical bearings in the control arms, right? So your setup is going to be GAZ shocks rear, GAZ struts (GAZ insert w/ OEM housing) front, GAZ upped spring rates front and rear, plus spherical bearing control arms? If so, wow, just wow. Looking forward to future reports...
 

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Discussion Starter #4
Good for you. These measurements are likely much better than you give them credit. The bathroom scale is probably pretty accurate at these low pressures... Still surprised at how soft the stock front springs are. And surprised that Ground Control's Insight kit comes with 425 lb/in springs (front at least). Is that right??

JoelR, you're the one with the spherical bearings in the control arms, right? So your setup is going to be GAZ shocks rear, GAZ struts (GAZ insert w/ OEM housing) front, GAZ upped spring rates front and rear, plus spherical bearing control arms? If so, wow, just wow. Looking forward to future reports...
Close; you forgot the most effective suspension upgrade of the bunch--a 60% stiffer rear "sway bar". My rear springs are un-cut Matiz springs. Given how much improvement I got with the stiffer rear axle beam, I'm having doubts the front damping/springs upgrade could possibly make as big a difference. We shall see!
 

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That's right, rear sway bar. Gone whole hog. Definitely cool... I may have to take a closer look at the sway bar option - seems not too difficult and maybe offers a good return in terms of performance increase. On the other hand, I'm just sorta vexed that there's no easy, straight-forward bushing replacement option for the control arms and engine mounts - as the looseness in these areas on my car undermines the purpose of any other suspension type mods. I'd probably try something with stiffer springs in the front before I did anything else. Maybe I'll have to break down and try something with the control arm bushings, too, just so I can justify doing the rear bar...

One more thing: have you really tested the car, hard, in terms of cornering balance and such - with the rear bar? With such a soft front I'd think the rear bar would be giving you too much over steer...
 

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Discussion Starter #6 (Edited)
That's right, rear sway bar. Gone whole hog. Definitely cool... I may have to take a closer look at the sway bar option - seems not too difficult and maybe offers a good return in terms of performance increase. On the other hand, I'm just sorta vexed that there's no easy, straight-forward bushing replacement option for the control arms and engine mounts - as the looseness in these areas on my car undermines the purpose of any other suspension type mods. I'd probably try something with stiffer springs in the front before I did anything else. Maybe I'll have to break down and try something with the control arm bushings, too, just so I can justify doing the rear bar...

One more thing: have you really tested the car, hard, in terms of cornering balance and such - with the rear bar? With such a soft front I'd think the rear bar would be giving you too much over steer...
I know what you're saying about the question of which improvements and in which order. I can't say with 100% certainty but as someone who has tried a number of changes mostly one at a time, I think a stiffer rear "sway bar" would improve the overall handling in terms of responsive turn-in regardless of the other upgrades & replacement of worn parts. To put it another way, unless your car has significant handling problems due to an outright part failure, I'd suggest doing the rear bar first. To answer the question of handling balance, no, I don't know what the at-limit behavior is in terms of oversteer/understeer but I'd like to know before I stiffen the rear beam further what happens at maximum cornering load if you completely let off the throttle or hit the brakes hard--does it snap to oversteer? I doubt it but will report back when I know for sure.

Assuming, as I have, that swapping out the OEM tires will kill mileage too much, I think my suggested order would be:
+60% (at least) stiffer rear axle beam
Better rear damping (via GAZ or even Monroe if your budget is tight)
Matiz rear springs (if damping above doesn't stop bottoming itself)
New OEM Lower Control Arms (spherical bearings buzz quite a bit but have some benefits)
+25mm rear spacers (just to reduce tramlining)

In the Unknown category of impact:
Stiffer front springs
Stiffer front struts
New/Upgraded rear axle bushings
Stiffer front sway bar
Chassis bracing
Lowering/corner weighting
Front caster increase
Front camber increase (beyond the ~-1 degree crash bolts can allow)

Joel
 

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....Better rear damping (via GAZ or even Monroe if your budget is tight). Matiz rear springs (if damping above doesn't stop bottoming itself)....
I tried the Monroes. I thought they were slightly worse than my stock shocks. I have ~150 lb/in cut miata springs in the rear that have worked great for quite some time. Also installed shorter bump stops rear, zero bottoming-out and no problems with bottoming out the shocks themselves (i.e. running out of compression damping, having the shock inner rod bottom-out in the casing)...
 

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LOL! That's exactly what I did for my spring measurements, except I used my mill.
My bathroom scale was rated to 400lbs, so I figured it would be reasonably accurate for the Insight spring test.

I used the quill stop to ensure that each loading was identical, and found the bathroom scale measurements to be very repeatable. After a series of measurements, I moved the quill stop for another 0.5" of compression.

FWIW, I found the front springs (the only ones I tested) to be somewhat progressive. I did a range of test loads, starting with 0.5" then up to 2.5" on 0.5" increments.
From 0.5" to 1.5" I measured a spring rate of 83 lbs/in. With 2"+ of deflection, I measured a spring rate of 98 lbs/in to 100 lbs/in.

I completely agree that a 425 lb/in spring mated with a damper designed for a 100 lb/in would result in lousy performance - unless your goals are to dump your Insight to the ground and cruz for trouble. ;->

All I did was put my digital bathroom scale on a scrap of 2x12 on the drill press table, added a scrap of plywood to the GLASS scale surface and used the drill press' built-in table height adjustment to create the right spacing for the several springs I had on hand. I took measurements by zeroing the scale, then cranked the drill press down exactly 1" in a series of 3 reading per spring.

Here are my results:

300 lb/in springs provided by GAZ: 276lb/in
OEM Insight springs (front): 81.3 lb/in (avg of 82, 78, 84)
OEM Insight springs (rear): 76.5 lb/in (avg of 75.5, 77. 77)
OEM Chevy Aveo springs (rear) (cut down a coil or so): 111.8 lb/in (avg of 109.5, 112.5, 112.5)
OEM 2010 Honda Fit springs (rear): 110.3 lb/in (avg of 109, 112.5, 109.5)

Caveat: Obviously a bathroom scale isn't the most accurate scale in the world and my methodology is a bit crude but I think you can safely take away from this some relative stiffness ratings.

I'm REAL curious how the car feels with springs 3.4x the stiffness up front than it came with. Considering Ground Control ship their kit with 425 lb/in springs, I cannot believe that spring rate w/OEM dampers even remotely works.
 
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