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View Full Version : Coil-over setup questions: Opinions please


2KWhiteSnake
04-11-2003, 03:05 PM
Ok... I talked to Chris at MM.
Here's what we came up with...for my 01 Cobra Coupe.

Front: Bilstein Race Valve struts with 425lb springs $369

Rear: Bilstein Cobra R shocks with 650lb rear springs $429

IRS bushings $50, C/C $199, and their basic Subframes $119.

He said that should get me started in a big way. Now I need to talk to the wife Guess I'll just skip the new seats for a while and go for this stuff and the cage. I can always use the harness with my stock 01 seats. They aren't too bad I don't think.

How does that setup sound to you guys?

Craig

98banana
04-11-2003, 09:14 PM
Didn't realize this thread was started. See my response in the otc thread...

Cobra-R
04-29-2003, 09:51 AM
Originally posted by 2KWhiteSnake
Ok... I talked to Chris at MM.
Here's what we came up with...for my 01 Cobra Coupe.

Front: Bilstein Race Valve struts with 425lb springs $369

Rear: Bilstein Cobra R shocks with 650lb rear springs $429

IRS bushings $50, C/C $199, and their basic Subframes $119.

He said that should get me started in a big way. Now I need to talk to the wife Guess I'll just skip the new seats for a while and go for this stuff and the cage. I can always use the harness with my stock 01 seats. They aren't too bad I don't think.

How does that setup sound to you guys?

Craig

Anybody know why MM recommends 650 lb rear springs and griggs recommends 475-500lb springs on the IRS Cobra's? Seems like a very large difference between the two. Both are pretty much in the same ballpark with thier front springs advice. Has anyone else noticed this?

Brian

2KWhiteSnake
04-29-2003, 11:22 AM
I wondered the exact same thing.

Craig

sn8kbit
04-29-2003, 11:45 AM
Brian, we mulled over this some yesterday, but we're both in the dark still.

The Griggs stuff for the rear I have came with 500# springs, went with MM's input and got the 600#. Fronts are 400#. Koni D/A's up front, Griggs valved Koni 30 series in the rear.

Doing the "internet search" on some boards, guys that have been out racing the cars complained that 450-500 wasn't enough spring in the rear, and replace with 650-700# and got very good results. I know it'd been reference that the rear has to be within a certain amount above the front rate, but 600 is quite a bit more than 400.

Talking to Jack out at OTC I came away confident I'd made the right decision on spring choices, although I'm still kinda in the dark as to why. I know that alot of the reasoning is the difference in arm lengths for the IRS, but beyond that, it's anyone's guess. I should have the car back this week to see what kind of difference/ride the car has.

Maybe we should move this over to the MM forum, and get Jack's input on the reasons for the difference.

2KWhiteSnake
04-29-2003, 11:56 AM
It did seem crazy to me also, since most of the reading I've gone on Corral.net, etc. suggest that you use a lower spring rate in the rear. This however, is on fox bodies. I have a hard time finding any info on the IRS cars. Any info I do find doesn't pertain to coil-overs. I understand that the IRS is heavy, etc., but I'm with you, 650Lb is a big jump, especially when there isn't near as much weight on the rear. Or at least there doesn't seem to be.

Craig

Cobra-R
04-29-2003, 12:10 PM
The thing that really has me puzzled is my car is what I would consider way to stiff for any kind of comfortable street driving. We gotta be missing something here. :(

BTW: I did call and talk to a higher authority on this issue yesterday after we talked, Steve. But I still don't feel reassured. hehe

sn8kbit
04-29-2003, 01:33 PM
I don't think it's a weight of the car issue. Even the stock springs are within like 80-90% of the front spring rate. The only thing I've found from Corner-carvers is that it's due to the different lengths of the IRS control arms. Do a search over there on "coilovers", there is a bit of interesting reading, no definitive answers tho...

Cobra-R
04-29-2003, 03:16 PM
Steve,
My question is why is MM saying one thing and Griggs something else? I have searched over there and talked to other people. Griggs people are accross the board (from my small sample anyways) running alot lighter springs than what MM is recommending to thier customers.
I am not comparing between a solid axle car and IRS, but between 99-03 IRS equipted cars.

At first I was talking to 03 Cobra owners about this and figured that maybe it was the heavier car or the revised geometry changes made in those cars. Now I have found people even back to 99 that are still getting the same 600-650 lb rear springs from MM and the lighter springs from Griggs.

2K,
Like steve was referring to (I think) you cannot compare spring rates between a solid axle car and a IRS. I run 250lb springs in my 95 and 475 lb springs in my 01. (both coilovers on Koni shocks/struts) Even spring rates between solid axle cars are going to vary alot based on what has been done to the rear suspension. Adding a PHB and TA, ect along with removing the upper control arms is need for significantly stiffer springs because you have eliminated some of the factory built in bind.

edited for spelling

2KWhiteSnake
04-29-2003, 10:57 PM
It's just confusing, even after reading on CC's.com for a while I'm actually worried about damaging my strut towers with coilovers. :)

There was a very lengthy thread on there about it, actually a few of them. Made for some interesting and very scientific reading. But still, I haven't seen but a few people say they've sustained damage from having them.

I REALLY want to hear from someone that has had both a good spring/strut combo, and later changed to coilovers. I'd love to know their impressions.

Craig

Cobra-R
04-29-2003, 11:18 PM
Craig,
I am no expert, but have run both ways. For a non serious track person with no intentions to go any further than a shock/strut change. I would say coilovers are over kill. (except if you want to be able to adjust ride height) Coil-overs do allow you to run a stiffer track type spring, while maintaining a better ride, but with a sacrifice in nhv.
If you have an ambition to go deeper into suspension mods ( MM or Griggs K-member for instance), then by all means go with coilovers.

Brian

2KWhiteSnake
04-29-2003, 11:36 PM
I'm planning on taking the car to it's Street/Open Track combo limit. It is my daily driver, however, I don't drive more than 10 miles a day, so if the ride is rough, it won't bother me anyway. Tom Lewis is going to build a 4-point cage for the car soon when he gets time away from the "banana #2". I'll be putting on subframes, new IRS bushings, and C/C plates(and new suspension components). That will be the extent of it for a while. I have an Eibach Pro kit on it right now with stock shocks/struts. I have a time fighting it on the track. The car has tons of body roll, and the rear end loves to slide. I just want the biggest bang for the buck I can get. I've about pushed the car as far as I can in its stock trim. I am running a much better tire than stock, which helped a bunch...it's the newer Kumho Ecsta MX's. Not ready for stickies yet...I still like the predictability.

Bottom line is....if a good spring with strut/shock combo will give me a great level of satisfaction, then should I just go with it?

Thanks for your input so far.

Craig

Jack Hidley
04-30-2003, 03:26 AM
I'm too lazy to host the attachment on my website, so you guys are going to have to do some work here. Download the attachment and rename it with an htm extension, then just open it in a browser. It's a couple of screens shots from an Excel spreadsheet we use for calculating optimum spring rates. There are three pages. One is basically a stock Cobra with IRS, two is the same car with 425lbs/in front coilovers and 650lbs/in rear coilovers, three is the same car with 425lbs/in front coilovers and 488lbs/in rear coilovers. I'm too tired to explain what it all means right now. I'll do that tomorrow.

Cobra-R
04-30-2003, 08:55 AM
Thanks, Jack.

I will have to rely on someone getting it hosted somewhere, I am to computer illiterate to figure out how to get it opened up. :(

Brian

2KWhiteSnake
04-30-2003, 10:38 AM
Originally posted by Jack Hidley
I'm too lazy to host the attachment on my website, so you guys are going to have to do some work here. Download the attachment and rename it with an htm extension, then just open it in a browser. It's a couple of screens shots from an Excel spreadsheet we use for calculating optimum spring rates. There are three pages. One is basically a stock Cobra with IRS, two is the same car with 425lbs/in front coilovers and 650lbs/in rear coilovers, three is the same car with 425lbs/in front coilovers and 488lbs/in rear coilovers. I'm too tired to explain what it all means right now. I'll do that tomorrow.

Thanks Jack, but you don't have any of the files the txt is pointing to. The file won't work. I had a couple of my admin friends look at it, and basically the files just aren't there they say. I'd love to take a look at it if we can figure out what the problem is.

Craig

Jack Hidley
04-30-2003, 01:08 PM
My bad.

I'll save it as mht format and repost it in a little while.

2KWhiteSnake
04-30-2003, 01:31 PM
Originally posted by Jack Hidley
My bad.

I'll save it as mht format and repost it in a little while.

Thanks Jack!

Craig:bounce:

Jack Hidley
04-30-2003, 03:39 PM
Since the file is an Excel spreadsheet, it won't compress into an MHT format. My web hosting is screwed up right now so that I can't upload at the moment. I'll post a message here as soon as I get it uploaded.

2KWhiteSnake
04-30-2003, 03:43 PM
Originally posted by Jack Hidley
Since the file is an Excel spreadsheet, it won't compress into an MHT format. My web hosting is screwed up right now so that I can't upload at the moment. I'll post a message here as soon as I get it uploaded.

You can email it to me if you'd like. cmathis@infoave.net


Craig ;)

2KWhiteSnake
05-01-2003, 11:30 AM
Jack, you still alive? :)

Craig

svt_coupe
05-01-2003, 01:11 PM
Craig - you are actually thinking about taking anything Jack says as accurate?? You are more of a risk taker than I am!!!!!

ha ha ha

(sorry... if I don't have anything to contribute, I should just shut my mouth)

2KWhiteSnake
05-01-2003, 02:02 PM
Originally posted by svt_coupe
Craig - you are actually thinking about taking anything Jack says as accurate?? You are more of a risk taker than I am!!!!!

ha ha ha

(sorry... if I don't have anything to contribute, I should just shut my mouth)

:rotf: :rotf: :rotf:

Craig

sn8kbit
05-01-2003, 03:58 PM
Originally posted by svt_coupe


(sorry... I should just shut my mouth)

All this time on earth, and you're just figuring that out? Must be the salt and pepper shuey wanna be hair....heh

svt_coupe
05-01-2003, 04:54 PM
I seem to like this guy lately:

:moon: <-- for Steve

2KWhiteSnake
05-01-2003, 05:32 PM
Originally posted by svt_coupe
I seem to like this guy lately:

:moon: <-- for Steve


Niiiice one Shugg. Are those corduroys he's wearing? :)


Craig:D

Jack Hidley
05-02-2003, 03:30 AM
Here it is, finally. Go to:

http://home.attbi.com/~jhidley/Index.htm

I'll explain what it all means later. Time for sleep.

2KWhiteSnake
05-02-2003, 11:20 AM
Thanks Jack,
Yep, I don't understand any of it, but that's pretty wild stuff. Is that measured while on the car some way?

Craig

Jack Hidley
05-02-2003, 04:32 PM
The link I posted is a level ride analysis for three different combinations of springs on an IRS equipped Mustang. The car in question has a total weight of 3600lbs and a front weight distribution of 56%. The first tab labeled "Stock Cobra" has stock spring rates and locations. The second tab labeled "Mod1" has 400lbs/in front coilovers and 650lbs/in rear coilovers. The third tab labeled "Mod2" has 400lbs/in front coilovers and 488lbs/in rear coilovers.

The spreadsheet is a simulation of what happens when the car hits a single bump moving at a particular speed. The graph shows three things. The purple curve is the vertical motion of the front suspension. The violet curve is the vertical motion of the rear suspension. The yellow curve is difference between the purple and violet curves. This represents pitching motions in the car. Vertical motions don't bother people very much in cars. Pitching motions on the other hand are very uncomfortable and must be minimized. Without going into a lot of the technical detail, the ratios of the front to rear spring rates affects how much pitching the car has at different. A proper design minimizes the pitching motions in the speed range where the car is driven the most. This is typically 65-75mph.

In the first simulation you can see that the magnitude of the pitching motions is very small. All production cars, when run through this analysis, will have similar results. When aftermarket suspension systems are analyzed for level ride, the results are all over the place. The second simulation is of a typical spring recommendation that we make for customers. The magnitude of the pitching is still very low, but not quite as good as the stock spring setup. The third simulation is what results if you take our recommendation and put softer (488lbs/in) spring place of the 650lbs/in springs. Now there is lots of pitching and the resulting ride will be much worse. It's important to note that putting SOFTER springs in the car makes it ride worse in this case.

After putting in the correct spring rates, the next step is to adjust the understeer/oversteer balance by tuning the car with the antiswaybars. If anyone wants to know what any of the parameters in the spreadsheet are, just ask.

sn8kbit
05-02-2003, 06:03 PM
Originally posted by Jack Hidley


After putting in the correct spring rates, the next step is to adjust the understeer/oversteer balance by tuning the car with the antiswaybars. If anyone wants to know what any of the parameters in the spreadsheet are, just ask.

That's hoping that there's a rear swaybar option for the IRS. I know there are options in stock sizes and aftermarket for the front, is there or will there be something to help the rear as well?

Preciate the input Jack.

--Steve

Cobra-R
05-05-2003, 08:59 AM
Jack,
Thanks for the info, but I have a couple questions.

1, Are these three scenario's using the same shocks? How would this be effected by a properly valved or adjusted shock to the specific spring?

2, What is the ideal setup for a simular car as in your example but for use on the track?

Thanks, Brian

on edit I was looking over the charts again and if I am reading it right, the shock dampening is the same on all three setups? I will rephrase my first question on that assumption and ask what will a properly adjusted or valved shock (to it's respective spring rate) do to these results?