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Looking in Demon Tweaks I notice you can get replacement springs of differring lengths, diameters and spring rates.
Length and Diameter I can find out so how do I find out the spring rate ,.. if I got a higher rate spring would that stiffen the suspension? If I got shorter springs (ignoring the fact I'd need to replace shocks) would I need higher or low rate springs,.... basically how does this stuff work??
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Only way to check your springs is by taking them off the car and either putting them in a coil spring tester. Or roughly by raisting a weight on the spring and measuring the compression. Then divide the weight by the how much it is compressed. A direct acted spring would normally be a lot lower rate than one that is acted on by leverage. ie. sierra mcpherson strut might be 150lb/in. rear trailing arm spring 500lb/in. Older haynes manuals used to say spring rates but not normally found in new ones
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*warning potential misinformation ahead* I think that if you chop down springs, the rate rises, making them stiffer. Therefore, if you bought shorter springs, and wanted to retain the rate of the current ones, you'd need to buy lower rate ones. I think. Actually, I don't know. Why did I post this?
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Also, some cars (Wedge VW Vans, Corsas etc) have "pigtail" rear springs, of which the diameter gets smaller, so that they'll compress to being almost flat. The spring rates for these work in a different way, that much I do know.
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HOW TO RATE COIL SPRINGS WITHOUT A RATER G=Torsion modulus for steel = 11.25 x10 6D=Wire Diameter in Inches N=Number of Active Coils D=Mean Coil Diameter in Inches. Mean Diameter is: I.D. = 1 Wire plus inside Diameter O.D. = 1 Wire minus outside Diameter 8=A Constant for all Coil Springs HOW TO DETERMINE ACTIVE COILS OF A COIL SPRING: Count total number of coils, subtract a coil for each coil that touches, these are dead coils. Ground flat ends are a dead coil. Start count with cut-off end facing you directly above would be one and so on. Not all coil springs are even coiled. You can have 1/4, 3/8, 1/2, 5/8, 3/4 or 1/8 of a coil (Example 10 1/8 coils). 1. If you cut one coil from a spring, the rate will increase. 2. Increasing wire diameter, will cause a great increase in rate. 3. Nothing in spring rate calculation indicates that a coil spring ever changes rate. The rate is determined by material and dimension of the spring. Coil springs don't wear out or lose their rate. 4. Spring load determines how much load a spring can support at a given height. The rate only tells how much height will change as load is changed. A spring can lose its load height over time if steel is not heat treated properly. When a spring sags, its rate is still the same as when it was new. Does that make sense?
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Last Edit: Oct 8, 2005 16:36:07 GMT by arthurbrown
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*warning potential misinformation ahead* I think that if you chop down springs, the rate rises, making them stiffer. Therefore, if you bought shorter springs, and wanted to retain the rate of the current ones, you'd need to buy lower rate ones. I think. Actually, I don't know. Why did I post this? The 'spring' is actually in the bar not the coiling, I believe...that's why a cut spring has a lower effective spring rate than an uncut version. So if you have a standard spring with 10 coils and cut it in half then it'd have the same strength, but over 5 coils...hence the higher rate. The lowering feature that I sent to datsuncherry had a good explanation of this and the difference that fulcrum points/leverage can have, including a neat formula to account for lever variations.
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Last Edit: Oct 8, 2005 16:35:45 GMT by rmad
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Ideally what you need is a press, a ruler and a set of bathroom scales(Digital peferably), you need to compress the spring slightly to pre load it while its sitting on the scales, measure the height and zero the scales. Then compress by 1" and read the weight on the scales. This will give you the poundage of the springs. HTH Dom EDIT : this can be done with a bottle jack as well, but do so at your own risk ;D
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Last Edit: Oct 8, 2005 16:37:22 GMT by CR500Dom
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HOW TO RATE COIL SPRINGS WITHOUT A RATER Yeah, 'swotImeant ;D
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I can see I'm going to need to get out there with a ruler!
If I want to stiffen the suspension do I need higher rated springs or what?? Anyone? Bueller?
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Depends what you want from the car. If you are happy with the standard cars ride quality but it leans a bit too much through corners you could always use a thicker anti roll bar. A good set of adjustable dampers can make quite a bit of difference in the way the car handles. If you want a very responsive, controllable car, you really need to go for a full package. A matched set of springs, dampers and a full poly bush set. Normally a 30% increase in stiffness would be a decent starting point over standard depending on how stiff they are as standard. MK1 escorts came as standard with between 110-135 lb/in front springs. Forest spec would normally be 170 lb/in tarmac 190lb/in. I run mine at 220lb/in on the front with a relatively soft back end for autotesting and it has very good turn in and lots of controllable oversteer but I wouldny recommend a setup like that for normal road use.
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