MechE00

How many of you stock class autocrossers have replaced your springs with a new set of OEM springs? Did you see benefits on course?

I am in the position to put a little money into my FC to freshen it up for autocrossing and to provide a few more years of faithful service.. was looking to put Konis in, but had an eye on redoing the old springs as well-- if it would pay dividends in handling and times.

I'm thinking about bushings too, but that would be another thread..

DamonB

I am considering the same thing and would be interested to hear other's comments. The springs are ridiculously cheap through Mazda Comp.

Cwaters

Damon, being inherantly lazy I'm going to ask you how much they are instead of looking them up myself.

Cory

DamonB

I only know how much the FD springs are. Your sig says you don't have one?

Cwaters

well yeah...that's true
guess I'll have to look it up myself after all...

redrotorR1

Should the SCCA ever come to its senses and bump the FD3S down into A-stock, refreshing the stock springs would definitely be on the top of my things-to-do list. Gee, return my car to stock .... that would only take me about a year.

C. Ludwig

iTrader: (27)

Springs don't lose rate over time. They will sag but if you start with a 400lb/in spring it will still take 400lbs to compress it 1". I've heard/read it's common among Showroom Stock racers to use "old" springs to lower their cars.

As long as one spring has not sagged a disproportionate amount compared to the others, altering corner weights, there should be no reason to replace them in an attempt to gain a stiffer spring.


Chris

MechE00

Hmm.. actually, according to a coworker who does creep tests in rubber and metal machinery mounts, the stiffness does change as the metal experiences creep.. he couldn't quantify the stiffness change, hence my asking around here.

If the showroom stock crowd find it advantageous, though, maybe the answer is that the stiffness loss is not a big deal, or that the suspension geometry change is more favorable than the stiffness change for their application..

Hmm.. think SCCAForums would be a good place to pick the brains of the Showroom Stock crowd further?

C. Ludwig

iTrader: (27)

Just know what I read.

turbojeff

iTrader: (30)

Hmm. Over time does the Modulus of Elasticity change? I don't think it does. The wire diameter of the spring doesn't change, MOE doesn't change, what makes the spring rate change over time? Nothing as far as I can see.

Ask yourself this question. If you had some plain old mild steel and some really trick alloy steel, both some standard sample size, would they deflect the same amount before yielding? Answer is almost all steels have the same MOE, ~28-30ksi. That means before the samples bend permanantly they both bend the same amount. The real difference is the alloy steel will bend farther before it bends permanently.

Otherwise don't waste your $$ on stock springs, go for Eibachs or something. Stock class in a FC is really a bummer. The FC can really benefit from a little negative camber up front. It makes it so much more fun to drive/auto-x.

The FD is awesome in stock form but Damon, switch to SM2, ASP or something. In competitive regions the FD won't cut the mustard in SS.

DamonB

This I already know. Problem is the FD is also uncompetitive in ASP (the Z06 bumps here too) and I am not willing to throw the amount of money it would take to make it competitive in SM2 either. I have put times up in SS that would have trophied me in SM2, I just prefer to run with the toughest then try and cherry pick so I can tell everyone I trophied. I enjoy the tough competition more than gloating.

redrotorR1

Or you can jump into SM2 and get kicked around by turbo Miatas. I always use the excuse that my car's not setup yet .... but those turbo Miatas are damn fast!

MechE00

Actually, material properties can change somewhat over time in certain applications.. I just don't know if automobile support is one of them.

Further, another contribution to the spring's stiffness is the tightness of its coils.. refer to this image:
http://students.bath.ac.uk/en8cc/progress.gif
Side by side is a linear and a progressive spring. It illustrates that for a progressive rate spring, you can change the spring rate just by changing how many loops per inch you have.

Hypothesis-- a sagged spring will have more loops per inch and thus be softer?

For further support, I present: http://www.mech.uwa.edu.au/DANotes/s...tro/intro.html specifically the developed equation t = K 8FC /pd^2 where p is the pitch distance between coils. A lower p (same as more coils per inch) increases the torsional stress for a given load--> lower spring rate..

On the other side of it... talking to the aforementioned coworker further, he's familiar with springs that can maintain a fairly constant rate over a decent range of deflection.. but these are typically smaller springs than automotive applications, and generally designed to become coil-bound before getting near plastic deformation.

I don't know the details and specifics of automobile applications, and since data always trumps theory, I was using this thread to look for data.. Of course, if I ever get off my lazy duff and track down some showroom stock guys, maybe I can have my data.. :p

thanks all!

DamonB

I think you are on to something there. I agree; it would have to be true.

I like turbojeff's explanation of materials but it does not take into account fatique. Obviously springs do sag after a time and must deform in order to do so; I reckon this is due to fatique.