How do I decide which springs to buy? - Alfa Romeo Bulletin Board & Forums
 
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post #1 of 8 (permalink) Old 07-27-2016, 05:25 PM Thread Starter
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How do I decide which springs to buy?

The springs on my S4 need to be replaced - the left side is 1 1/2 inches lower than the right side. The goal is to have a car that is fun to drive but recognizes that roads have dips, bumps, cracks, and holes. It appears that a lot of springs offered are designed for racing and "fast street" use. My understanding is that lowering springs significantly change the roll center's (RC) location and might even be detrimental to the S4's handling. Handling is determined by the relationship between the RC and CG, not by a low CG. I would need to model the suspension to understand the impact of a changed RC.

If vendors provided spring rates I would not be be writing this post. Unfortunately, they don't and they don't provide information wire diameter, coil diameter and number of coils that can be used to calculate the spring rate. If anyone has information on spring rates or information that can be used to calculate spring rates, it would be appreciated if you would share it.

The S4's factory springs provide the Spider with a natural suspension frequency of 1.1 cycles per second (cps) in front and 1.4 cps in back. I would like to have a front suspension frequency of 1.4-1.5 cps. The Spring Database I downloaded from the alfabb says most of the front after market springs have a spring rate of 1100-1200 lbs/in which produces a front suspension natural frequency of 1.8-1.9 cps. It alludes to the Alfaholics front springs' spring rate being between 600-800 lbs/in.

To come up with the natural suspension frequency I assumed a 50/50 weight distribution, calculated the front suspension motion ratio (MR) to be 2.5, and the rear suspension MR to be 1.19. The approximate sprung mass supported by each front wheel is 535 lbs. and approximate sprung mass supported by each rear wheel is 500 lbs. I used the Spring Rate Calculator rev3 spreadsheet for the calculations.

I'll update the spring database over the next few weeks with the listed spring's natural frequency.
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post #2 of 8 (permalink) Old 07-27-2016, 06:43 PM
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Did you ever get a final number for unsprung mass?

I bet your springs are just fine, but that your two spring pans are the same rather than a deep one on the right side. http://www.alfabb.com/bb/forums/spid...ring-pans.html

Chris

1990 Spider Veloce
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post #3 of 8 (permalink) Old 07-27-2016, 06:58 PM Thread Starter
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I'm familiar with the spring pan on each side having different depths. I measured the diameter of the front springs and it was the same as the diameter of the factory springs, 16.3 mm. I doubt if the spring pans have been changed, but I will check.

When braking I find the front end dive to be excessive and am hoping stiffer springs with matched shocks will remedy it and improve transient response. As I study suspension design I'm beginning to believe it is a study of interactions and trade offs which are not obvious.

The person I bought the car from weighed over 300 pounds. The driver's seat was demolished and driver's door panel was held on by large sheet metal screws. The more I work on the car the more "creative solutions" I find.
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post #4 of 8 (permalink) Old 07-27-2016, 07:07 PM
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No, no....read the linked thread closer. Nothing has been changed (so my theory goes!) - rather it came out of the factory wrong. I haven't found anyone yet (out of an extremely small sample size) that has a late-S3 or S4 with the different depth spring pans. And they all sit kinda funny. It's easy to correct and then they sit right. Do yourself a favor and make them right while you have it apart.

Wanting to change them for performance is a different conversation and understandable - there was nothing at all wrong with my springs when I changed them out.

The driver's door panel thing is common. The factory hardware includes a single-use grommet and if you don't know that you can't figure out how to properly re-attach it. Or you just don't care so you drive a decking screw in and call it good!

Chris

1990 Spider Veloce

Last edited by GV27; 07-27-2016 at 07:10 PM.
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post #5 of 8 (permalink) Old 07-27-2016, 08:37 PM
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I recently purchased an installed the Alfaholics fast road package with their "B" type springs. As far as I can tell it does not drop the car much or at all from the stock suspension that was on the car. In their description they say that it drops the car about an inch but I think in my case it actually stayed the same. I suspect that the old suspension was tired and worn to the point of sagging.

I just finished the work this past weekend and have not been able to drive the car on an really spirited drives just yet but from the few drives I have put on it I would highly recommend that package. It is firmer but does not make the ride harsh at all. In fact I believe the car is smother and less hash with the Alfaholics suspension that the stock one was.


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Originally Posted by GV27 View Post
No, no....read the linked thread closer. Nothing has been changed (so my theory goes!) - rather it came out of the factory wrong. I haven't found anyone yet (out of an extremely small sample size) that has a late-S3 or S4 with the different depth spring pans.
When taking my 86 apart I had a deeper pan on the driver side and the shallow one on the passenger side. Before I rebuilt the suspension the driver side did sag quite a bit more than the passenger side.

After the rebuild I swapped the pans around and now the passenger side is half a cm shorter than the driver side. From my understanding this is by design.
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post #6 of 8 (permalink) Old 08-28-2016, 08:16 PM
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Any updates on the ride? I'm getting ready to pull the trigger on the Fast Road Kit B for my 72 GTV. I've got Koni reds and the centerline suspension rebuild kit in a box.

Did you replace the front and rear spring pads? How about any bushings? I'm new to all things suspension - any help is appreciated.

Michael

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post #7 of 8 (permalink) Old 08-29-2016, 05:20 AM
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Many spring rates are listed here - http://www.alfabb.com/bb/forums/susp...-database.html

Ed Prytherch
79 Spider
76 Suzuki GT500
2011 Jaguar XKR

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke
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post #8 of 8 (permalink) Old 08-29-2016, 07:03 AM
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Quote:
Originally Posted by Pytelm View Post
Any updates on the ride? I'm getting ready to pull the trigger on the Fast Road Kit B for my 72 GTV. I've got Koni reds and the centerline suspension rebuild kit in a box.

Did you replace the front and rear spring pads? How about any bushings? I'm new to all things suspension - any help is appreciated.

Michael
Hi Michael,

This is taking the thread off in another direction a bit but make sure you read Vintre's "for dummies" suspension change threads:

http://www.alfabb.com/bb/forums/spid...e-dummies.html

http://www.alfabb.com/bb/forums/spid...e-dummies.html

Take a close look at those and others about suspension replacement part quality. It's been very spotty over the years. When I did mine a couple of years ago I had originally budgeted for the Centerline rebuild kit, but ended up almost doubling the cost on that budget item. The tie-rod ends in the kit are their basic items (Frap) that have a very bad reputation for longevity - you might be better off with their "premium" (Lemforder) joints. The bushings in the upper control arms can be an issue as well. Centerline says they're better now, but they have a bad reputation and a lot of people recommend replacing them.

If the bushings haven't been replaced recently, you should do all of them. Spring pads? See what they look like. If they're mangled, cracked, whatever they should probably be replaced but otherwise they should be fine.

Chris

1990 Spider Veloce
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