ES2K

My '06 is stock, running Michelin PSS, stock size, stock rims. I DD the S2K with spirited canyon runs, occasional track days.
I have run the Koni yellows on a past car and was very pleased with their performance and adjustability. The GC complete coil over package is valved to match spring rate. From what I have read, the swift springs are better for DD because they may provide for more travel. I am considering 10Kg front, 8Kg rear spring rate. My big question: Will Swift springs provide a better DD ride than comparable rate Eibachs? Other mods may include a CR front sway bar and an alignment that is more aggressive than the UK alignment. I intend to run stock height; no lowering.

Apex1.0

The ride is largely going to be determined by the damper and the Koni is a good choice for a DD. If the free length and rate are the same between Eibach and Swift, I would expect similar spring performance. In my opinion there are two kinds of spring brands. Known quality premium manufacturers (Eibach, Swift, H&R) and unknown, aftermarket stuff that may or may not be good. There is no reason to take a chance on anything from the second category, however there is no magic spring either. If its a good brand and specs match, they are the same spring IMO.

s2000Junky

I dont agree entirely with Apex on the idea that a quality spring is a spring. Having run Eibach springs in the past and Swift currently, ive learned that its not quite as simple as just comparing spring rates and name brand versus not etc. Swifts are more compliant for a given spring rate period. They have a superior coil design and material which allows them to be more bump responsive/compliant without giving away spring strength for the desired application. For example, on my current set of dampers I ran 10k springs which were a typical close coil design, and then moved to a 14k Swift and the bump response actually improved slightly which I was not expecting at all moving up 4k in rate. The car is stiffer but works better, it was well worth the $400 upgrade. They actually made the damper settings more effective across the board. Eibachs are old school and harsh, however if you don't experience any better, they can feel like an improvement, and are in some ways to a softer factory coil.

Apex1.0

In fairness I have never done a before and after swift to non-swift. I have been in cars with swift springs and there is really no way to tell what effect only the spring has on the way the car rides or handles.

It seems like they are a very good spring, however there are other good springs. I am just not sold that swift is somehow better than other quality springs.

You would have to show me some objective data, spring dynos and cycle tests or something....

//steve\\

If Swift was so superior to all else on the market you'd see them on the highest levels of motorsports but there is a pretty even mix. The biggest thing I hear against Swift is their ability to maintain rate over an extended period of time. This is where Hyperco has a good reputation. Sure they are heavier and might hit coil bind a few mm sooner but they'll maintain rate consistently the longest. Ive also run Eibachs numerous times with zero complaints.

Don't put too much thought into it.

Car Analogy

But in motorsports its all about lap times, not ride quality. S2000junky was referring to ride vs spring rate, one brand to the next.

Yes, all his comments were subjective, with no real data to back it up, but then data on ride compliance vs spring rate would not be easy to come by.

Intuition tells me rate is rate, if its more compliant then its a softer rate. But who am I to argue against someone's actual experience, when all I have is what seems right in my mind. I've been wrong before. Not often, but it does happen

ES2K

Thanks to all for your input.

8.5kallday

I currently have swift spec r springs on my 06 ap2. Even though the lowered height of the car is spot on perfect I wouldn't put Swifts on ap2 shocks again. My ride is softer that stock but has a pogo stick effect that it didn't have before so it's bouncy over big bumps n dips. I've had them for about a year and the tide has gotten softer but I say it's the shocks getting older and not the springs since Swifts don't settle from what I've read. If I could do it all over again I'd get either cr shocks or koni shocks w the Swifts and not ap2 shocks.

Andersonracing

I havent experienced swift or eibach springs on my s2k but I have used both brands on my race cars for a long time. I highly recommend the Swift springs over the eibach (not saying eibach is bad)

The swift springs will give the same spring rate at any compression. If you dont know, lets say you have a normal 250lb spring. as it compresses that spring rate goes up some times as much as 20% and also lose overall height after some time.
Swift springs have a barreled design which gives it the nice property of maintaining the same rate. The quality of their springs is amazing. After a full season the springs I was using did not lose any overall height and maintained the appropriate rating(I dynoed my shocks and springs 3 times a season).
Though you may never race the car or get it that low for that matter, the barreled design also helps keep you from coil binding. This is when the coils of the spring compress so far that it becomes one solid mass. In some racecar setups this is desired but for a street/track car I would stay away from it.

Just a side note, What ever you decide on you can call Racecar Factory in Irwindale,Ca. They can help you pick your spring rates and help you set corner weights, cross, right height etc.

DavidNJ

This isn't true. A steel spring is a steel spring. All steels (and even cast iron) have approximately the same modulus of elasticity. Where the different alloys and possibly quality come into play is in how long it takes for them to fatigue (or if they fatigue) and the weight of the spring.

This is because different alloys have different yield strengths. The hire the yield strength the more the spring can flex before it deforms plasticly (like bending a paper clip too much). Hypercoil and Swift appear to use thinner wires and fewer coils for a specific rate and length. That makes them lighter and allows them to compress more. For an 8" 2.5" diameter 10k spring that may be 4.7" vs. 5.1". However, because there is less metal, it is slightly lighter. Nothing anyone would notice unless you are in a race were hundredths of a second count.

Swift, Hypercoil, and Eibach all make top quality springs and are widely used in racing. There are lots of other spring manufacturers (e.g. Afco, Integra, etc.) plus really cheap imports. Some of these many undergo high cycle fatigue. 20 years ago it was very common to check those coil springs regularly for rate (the rate goes down as they fatigue). Not as much any more. If you look at the various racing tool providers a coil spring tester is a pretty common tool.

Sidebar: The modulus of elasticity is also known as Young's Modulus after Thomas Young who wrote about in 1807. Young was involved in lots of things and was heavily involved in deciphering the Rosetta Stone, itself discovered in 1799 to understand Egyptian hieroglyphics.

Ride is impacted by the shock and the spring. A good shock can make a fairly big difference.

The Koni fit a need for a rebuildable, adjustable shocks at a low cost. Times have changed and there are several decent rebuildable monotube shocks also at relatively low prices. There are lots of threads on the topic. Two recent ones are Bilstein PSS9 -vs- HKS GT IV and Battle of the $1200 coilover! . You may also find My Fortune Auto 510 series review, Fortune Auto 510 - Spring Rate & Valving Opinions, Fortune Auto 500 Series Coilover Review, Ohlins DFV and Urge review, Ohlins DFV's installed , and HKS Hipermax iv GT coilovers interesting.