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Old 05-19-2009, 03:52 PM
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Coil spring mount and selection questions

I need help

I can Design and build the Upper and Lower Coil Spring mountings that I need for my IFS, but I lack the experience of actually setting up Coils. I understand I can’t actually select a spring rate without knowing the final vehicle weight. So I need to find someone or a business with experience to ask them questions such as clearances, spring length and a couple other questions including sources of good springs and shocks.

So if anyone feels they could answer a few questions or knows of a friendly neighborhood spring man please post a reply.

Thanks: Iceman
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Old 05-19-2009, 05:13 PM
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For a quick reference...the Chevy Trailblazer uses a 85 and 175 pound springs, the lighter ones in the front.

If you set the springs directly over the rear axle, then you'll get the measured amount of compression and the stated spring rate. If the spring is say, halfway up the control arm, then you'll get half the compression at the axle and double the spring rate.

For the front...take a look at the Chassis Engineering Mustang II front crossmembers. The design uses a jackscrew to provide roughly 2" of adjustment on the top coil spring mount.

I'm no expert, but I'll do what I can to answer your questions. Just let me know.
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Old 05-19-2009, 07:16 PM
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I need help

Quote:
Originally Posted by hinklejd
For a quick reference...the Chevy Trailblazer uses a 85 and 175 pound springs, the lighter ones in the front.

If you set the springs directly over the rear axle, then you'll get the measured amount of compression and the stated spring rate. If the spring is say, halfway up the control arm, then you'll get half the compression at the axle and double the spring rate.

For the front...take a look at the Chassis Engineering Mustang II front crossmembers. The design uses a jackscrew to provide roughly 2" of adjustment on the top coil spring mount.

I'm no expert, but I'll do what I can to answer your questions. Just let me know.

You stated
"If the spring is say, halfway up the control arm, then you'll get half the compression at the axle and double the spring rate." That makes sense.

I know spring angle has a similar effect that can be calculated. So if i calculated spring angle and spring position in relation to weight and subtract from Coil spring Rate. That should get me closer to the spring rate required to support the truck at ride height? I need to think on all that.
Any place that has math on that?
To see what i am working on see http://www.icemanproject.com
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Old 05-19-2009, 07:59 PM
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I took a look at your site... the truck is in a hell of a good shape for as old as it is. But I've got to ask - why independent? The truck has a well engineered suspension system in it already, why go and try to reinvent the wheel? The leaf springs have held the axle in place for the past 80 years. To convert to coil springs would require more than just coil spring selection and upper and lower pockets. You'd also need to locate and fabricate control arms and mounts, figure out how the compression and flexion of the axle would affect the bump steer, and probably exceed the factory steering capability, so that would have to be redesigned as well.

Your site doesn't have anything in the 'Concept' section, so I don't know what your goals are with this vehicle. But if you're looking for a static drop or lift, there are easier ways than trying to refit coil springs where leafs came originally.
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Old 05-19-2009, 09:44 PM
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I need help

The IFS is almost done, way over built with off road control arms 1.25 upper and 1.5 lower heavy DOM. Most of it is made out of 1/4" steel, and R&P from 3/4 tone truck. After 3 attempts using CAD and Suspension design Program I got it all aligned up and got .018 bump. see photo.
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Old 05-20-2009, 01:02 AM
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That's all looking good, from what I can see in that photo. What application are the spindles designed for? What steering are you using?

If you can build a lower spring pocket inside the lower control arm, then your upper spring pocket position should be determined by the length and rate of the spring.
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Old 05-20-2009, 07:56 AM
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Those look like lifted spindles from a S-10 baha kit. You position your upper spring mount in as far towards the frame as what you need to clear the UCA, and as high as you can.
The motion,(and force) ratio for most setups is about 2:1.
The motion ratio is determined by finding the spring mounting point (force) along the lever arm. The lever arm is a line created when you intersect the center of the contact patch of the tire at ride height,(load) through the LCA bushing.(fulcrum) The tangent angle created by a line from the lower spring mounting point to the upper mounting point can be calculated as well, once you know your weight at the tire contact patch.

The spring can be put as far outboard on the lower control arm as possible, but I've been told that having the spring closer to the ball joint can result in a harsher ride. Moving the spring inboard of course will require a stiffer spring.

If it were me, I'd pick a spring basic dimension that was commercially available in several rates, use those dimensions to mock up the mounts. Eaton Detroit spring has MII springs available in 23 different rates, but all have the same basic OD. You want to have about 1/3 of the travel of the installed spring taken up by the weight at ride height, but you need to find your suspension travel, so that you can make sure the spring does not come close to binding. I know that if you choose to use a larger spring, the stock car racing suppliers have many rates available in the same basic spring dimension. I'm sure a call to Eaton Detroit would help you in that area as well.

I have 2 books at the shop that have the calculations, which I'll put up later.. I'm sure there are online calculators as well. Billy Shope's webpage is down,(due to excessive traffic ) but I'm sure he has the proper way to determine your motion ratios and some spring calculators on there as well.

The spring packaging in your suspension design is the first consideration, then pick a spring rate to hold up the car. You can keep in mind that the longer spring you use, the less of a rate you will need.

You can design a spring jack into your upper mount, to simplify getting the ride height correct after you find a good rate. Speedway motors sells several, as do most of the stock car suppliers...once you see one, you will see it's easy to fab one up.

I don't think anyone can really calculate an exact spring rate on paper the first time out, but you can get close, but the proof is in the ride. Until you have an actual weight of the truck with the tires on the ground, and the body on the frame, you are going to have a rough time calculating any kind of spring rate.

Eaton Detroit spring chart, rates from 308-461#
http://www.eatonsprings.com/m2coils.htm

BTW, Your thread title was changed, to accurately describe your question.

Later, mikey
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Old 05-20-2009, 09:58 AM
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Ok there are more calculations and several explanatory drawings in the books I have than I can really put here, and if you have not done so already, you would do well to pick up a copy of Herb Adams book, "Chassis Engineering", or any one of the chassis design books by Steve Smith.

If Billy Shope's website comes back up, that would be worth a look as well.

Later, mikey
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Old 05-20-2009, 01:20 PM
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I need spring help

Thanks
You have a good eye the spindles are of a GM design with a 3” lift. During the design process I quickly found out that if I wanted to keep the wheels inside the wheel wells I was going to have to get creative. So the “A” arms had to be short, above and below the frame and as far inboard as possible. The spindles also keep the ground clearance up so the beast maintains a stock look. The rest of the parts are more or less off the shelf for convenience including the GM truck R&P.

It was too late for me to call Eaton Detroit yesterday so I emailed Mike over there to start with. I have a lot of calculations here also but placement and a C notch will probably come down to where the springs will fit. I can go up and down a lot with the upper mounts, but I have to find springs like you mentioned in an OD and size with a wide range of rates. The “about 1/3 of the travel of the installed spring taken up by the weight at ride height” answers a question I had.

The information in your post is very helpful to confirm or to give me something to look into from a real world source, which is what I was looking for. I think I have one of those books.

So keep the information flowing, I don’t want to redesign at the end.

MIKE
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