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Old 02-14-2011, 11:15 AM   #1
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Default Suspension question, fabrication

I actually have a ton of work done to my rear suspension and also fabricated better sway bars for front and rear, I'm now looking into some smaller performance things for the front, I have created in CAD some new coils for the front that lower the car 1.5 inches and are about 30 percent stiffer, so my question...

With all my calculations of the material and springs, The tires should not rub the inner fender wall, any opinions on this as a double check?

Also, when installing these, is this going to create some sort of pogo effect that other cars experience when lowering?

And could I still use my stock struts? I have fairly new Monroe struts in now that are a little more heavy duty than stock.

Thanks, I Just need my school to order the metals and then I can begin manufacturing the springs, depending on how everything turns out, I'm willing to manufacture more for anyone that wants a pair, keep in mind the coil end configuration is the same as oem, so it'* just an easy install. Also, professors here are helping me determine the metal, spring coefficients, and reliablity factors as well. These are all professional engineers.

I'll try to post up the CAD drawing and calculations later.
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Old 02-14-2011, 12:09 PM   #2
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Search on lowering and 95nasta. He lowered his Bonnie by swapping soem parts out and it looks great.
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Old 02-16-2011, 08:16 AM   #3
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Yeah, I have his full write up, I believe he used some grand prix parts and the had a full coil over setup, I was just going swap out the springs for my fabricated ones.
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Old 02-17-2011, 02:16 AM   #4
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Pics of the sways?

I'm assuming you corner weighted the car to determine drop and spring stiffness with your new fabricated springs? If so, what are your numbers?

Do post up calculations. As an engineer, I would like to see them.

Also, what did you come up with as a stock FE1 spring rate?

FWIW I did a 2ish front/1.75 rear drop springs that were probably in the neighborhood of 40% stiffer (than FE1) with OEM replacement KYB GR2s. I've read that KYB GR2s have a 15% increased dampening compared to stock. I doubt Monroes are going to be much beyond that. Either way, those shocks/struts could not keep up.. especially in the front, which is why I went to an adjustable front strut.

Your best option is to find a front GP lowering spring with the least amount of drop, GP AGX front struts, 00+ knuckles/hubs, whatever 12" brakes you choose, and the little tweaks outlined in my write-up.

And past 2" is when you have to worry about tire rubbing up front. In the rear it'* more offset dependent on wheel offset. Stock 40ish ET with a 7/7.5" wheel you'll be fine but if you start getting into the 20s you'll need to roll the rear fender lip.
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Old 02-18-2011, 09:43 AM   #5
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I have not yet made the coils, it'* still all in the design process. I'm goin back to college in about two weeks. if I can't get my data sheets with in that time I'll post them as soon as I get them. I'll try emailing my professor to see if he can send them to me. I honestly forget the stock spring rate. There'* a full analysis on the stock coils and stresses/strains done in solidworks.

I'm not lowering the rear, just the front...and also only about and inch to Inch and a half. Looking through your write up, you used the GP assembly for most of your conversion, but the struts you have on now, are they GP manufactured struts? You stated the KYB GR2 struts were a 15 percent dampening increase, were the KYB GR2'* maufctured for the bonneville, or were these made for the GP. I havent done my analysis on the struts yet, but was hoping to use the Monroes which are on the car now since they are pretty much new. With only a 1 inch drop I couldn't see there being too much of a difference? And did you expeience a pogo effect when you used those KYB'* for your drop?

Also, what school are you going to/went to? I see you are in Philly...I'm close to Allentown.
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Old 02-18-2011, 06:53 PM   #6
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Pics of the sways you fabricated?

IMO there is no need for an analysis of the stock coils in soildworks or stress/strain data.

Do post up your calculations you mentioned earlier.

I have W-body KYB AGX front struts. I cut the spring perches off and made coilovers out of them when I decided I wanted to go lower than W-body Eibachs got me.

The 15% increase was stated for a W-body GR-2. I would have to assume the Bonneville would be the same.
Yes, I had pogo on the highway at speed with GR2s.

So you designed 1" and 1.5" drop springs?

I went to Temple and I am currently pursuing my Mechanical Engineering masters at Villanova.
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Old 02-18-2011, 08:36 PM   #7
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But did you use aluminum control arms from the later revision H body or?
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Old 02-21-2011, 08:16 AM   #8
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I'll post up the data as soon as possible, just emailed my professor to see if I can get the sheets from
Him, the reason I did some analysis in solid works was to see if there is any other type of material I could design the coils from, and also different geometries of the coils. And no, I have yet to design either of the coils, as of now I just have the stock analysis almost done.

I'll try to get the pics up as soon as it'* a good day here, it'* been raining and snowing the past two days.

Also, I'm trying to lower the car as much as I can, without going into the wbody setup, I would really prefer to go am inch lower, and still use the struts on the car, not sure if it'* possible anymore though, which is why i proposes that question.
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Old 02-21-2011, 12:42 PM   #9
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I put my BonnevilleGXP down to the tires. I regretted it. Ruined the sway bar bushings and end links, and chopped tires twice. 18k miles on OEM RSA'* and 19K miles on gForces. Lowering more than an inch or so really requires you take other steps like finding struts that wont bottom and dealing with OEM non adjustable camber. I did it with airtrut/airbag combo'*. 95nasta did it with just spring alterations.
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Old 02-21-2011, 07:04 PM   #10
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Quote:
Originally Posted by billythekid View Post
I have created in CAD some new coils for the front that lower the car 1.5 inches and are about 30 percent stiffer
Quote:
Originally Posted by billythekid View Post
And no, I have yet to design either of the coils, as of now I just have the stock analysis almost done.
I'm just going on what you said.

A 1" drop would probably be ok if the spring rate increase isn't much over FE2.
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