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Old 02-01-2005, 12:03 PM
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spring rate?

Last year I purchased a rear coil over kit from some place online(I dont remember who but it is very similar to the comp engineering setup) Cuurently the body is on the car and I am ready to put in the fuel cell, but I am starting to wonder if the springs in the rear are to weak. The car by the way is a 71 vw bug with a full frame and roll cage, the only thing left of the vw is the shell of a body, not more then 300lbs.

The springs are 10" tall free and about 3.5" od diameter. The weight of what I have right now compresses them to 7" and I am running out of adjustment room to get the stance I want, the 12+gal fuel cell and battery are not even back there yet!. I am not overly concerned with having the suspension being race ready, for it will only be a streetrod.

I guess what I am getting at is what spring should I buy? I am what would be a good spring rate so it does not sag so much?
any help would be great!

got some pics in my gallery

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Old 02-01-2005, 01:48 PM
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First get the ride height set. measure the free lenght. Then weigh the rear and purchase the rating that suites the need.
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Old 02-01-2005, 04:44 PM
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Just to add some numbers to what "johnson" has already told you, suppose the only place you can conveniently support the chassis, with some wheel scales, is 125 inches back from the front wheels and that those scales indicate a weight of 1382 pounds. But, the springs will be located 108 inches back from the front wheels. This means the springs will be supporting 125 over 108 times 1382 or about 1600 pounds. Then, suppose you want the springs to deflect 3 inches from free length. That would mean a spring rate of 800 (half of 1600) over 3 or 267 pounds per inch. The spring catalog probably has springs of 250 and 275 pounds per inch, so you make a choice.

The above assumes the coilovers are mounted vertically. If mounted at an angle from the vertical, divide by the cosine of the angle before going to the catalog.
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Old 02-02-2005, 03:04 PM
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thanks for the help, I will do some calculating this weekend!!
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Old 02-03-2005, 08:19 AM
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Billy, I'm confused!! If the wheel scales measures 1382, is that not the weight the rear wheels are supporting and should not your calculations be based upon the weight to be supported? Your formula increased that weight so please clear up my confusion.

Trees
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Old 02-03-2005, 01:29 PM
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Take it to the extreme and it might be clearer. Suppose you glued a 5 mile long horizontal weightless rod to the trunk of the car. If you then walked back to the end of that 5 mile long rod, you could support the weight of the car with your little finger.
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Old 02-03-2005, 05:57 PM
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Billy, I re read your post about 3 times and now know what confused me. I locked in on wheel weight and not weight some what aft of the wheels. Now understand.

By the way, where can I find some of that weightless 5 mile rod?

Trees
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Old 02-04-2005, 04:20 AM
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Yes, I understand. When I said "wheel scales," you automatically slipped them under the wheels and assumed the springs were directly above. But, the wheel scales can be used to weigh most anything, including my neighbor's fat wife.
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