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Not sure, but make sure to look at Swift. I have been really happy with the street feel of these. I am not a fan of Eibach. The swift are progressive and sit the car about an inch lower than stock. However the feel is the same, I cant tell the difference, in fact, the COMFORT mode actually feels more comfortable! On the stock springs I could switch that switch all day long on different pavement and never feel the difference. You can feel the difference with the swift. I look forward to hitting them hard on the track.
 

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Not sure, but make sure to look at Swift. I have been really happy with the street feel of these. I am not a fan of Eibach. The swift are progressive and sit the car about an inch lower than stock. However the feel is the same, I cant tell the difference, in fact, the COMFORT mode actually feels more comfortable! On the stock springs I could switch that switch all day long on different pavement and never feel the difference. You can feel the difference with the swift. I look forward to hitting them hard on the track.
I've been considering the Swift ones as well, even the MCR version of the Swift springs looked pretty interesting. Springs are springs, though....wonder how much different they would be compares to the H&R ones. Wasn't there an H&R sponsored GT-R at SEMA?
 

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I spoke to David Cortez at Eibach today about their spring kit and about the stock GT-R spring rates. He was very helpful and here is what he told me.

Stock spring rates (Eibach's own measurements on a GT-R in Germany):

Front : 119 N/mm average rate (0, +- 20 mm deflection, +- 40 mm deflection). Max rate is 151 N/mm or 862 lbs/in. At static ride height, rate is 140 N/mm or 799 lb/in

Rear: 67 N/mm average rate (0, +- 20 mm deflection, +- 40 mm deflection). Max rate is 78 N/mm or 438 lbs/in. At static ride height, rate is about 68 N/mm or 382 lb/in.

Eibach spring set rates (product # 6389.140):
http://eibach.com/cgi-bin/htmlos.exe/08142...421399500022212

Front : average rate not given. Min rate is 399 lb/in. Max rate is 948 lbs/in. At static ride height, rate is 948 lb/in as soft coils are touching.
Drop is 0.8"

Rear: average rate not given. Min rate is 188 lb/in. Max rate is 485 lbs/in. At static ride height, rate is 485 lb/in as soft coils are touching.
Drop is 0.5"

They use progressive rate springs to essentially control the static ride height (saves using a second tender spring and spacer), and with their design, the static spring rate is the same as at full compression. Their goal was to increase front and rear spring rates by a modest 15-20% and to slightly drop the ride height. That way dampers can handle the new springs without requiring a change in valving.

I asked about sway bars and he said he did not see any notice of current plans to build some, but he did not rule it out. Their director of R&D is away and I will try to get some info from him in January.

They have a very good price for that kit of 4 springs.
 

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Swift/MCR's

Spring rate:
Front 5.4kg to 15kg, 302lbs - 840lbs
Rear: 2.4kg to 7.0kg, 134lbs - 392lbs

1" drop

ill probably get these or the eibach's in conjunction with the Cobb sway bars (and bushings) and call it a day with 19" wheels and tires...

whats the price of the eibachs from them?
 

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okay, bought ;)

or i could have had the box say "mines" for another $500...hmmmm... tough choice
 

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IMHO, Cobbs coilover kit offer the best "spring rates" out the box and will increase handling. The other springs that I've seen are WAY too soft in the rear and will promote understeer.
 

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I was a skeptic of Swift Springs. The price was about double of the Hyperco, Eibach, and other springs we were running on the race car. They weren't expensive, but more than what I was paying.

After I got a couple sets of Swifts - spend the money on them. They are nice. Very light. About 1/2 the weight of the other springs we had on the car. They worked out well for us, and I really liked them.

Spend the little bit extra on them.
 

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Actually those rates I got from Eibach sound just right for the stock car based on what other packages are setting their spring rates. Here are the rates for the Nismo ClubSports package:

Front: 181 N/mm - 18.5 kgf/mm - 1036 lbf/in.
Rear: 94 N/mm - 9.6 kgf/mm - 538 lbf/in.

So the fronts are 1036/862 or 20.2% higher than OEM at max deflection and for the rears are 538/438 or 22.8% higher than OEM. Since they don't change the sway bars, the Nismo package stiffens the rear slightly more than the front and thus have tuned the car for a little bit less understeer.

Notice also that Nismo has hardly changed the damper valving in the front and that for the rear they have increased the bump valving a low shaft speeds (handling part) and slightly reduced the high shaft speed rebound valving (slightly less stiff for driving over bumps). Stiffening the rear bump valving at low shaft speeds will also reduce understeer, since when you enter into a corner, the outside rear goes into bump and a stiffer damper valving adds to the stiffer spring rate and transfers more weight at the rear for less grip there and thus less understeer. I would assume Nismo know what they are doing in tuning the GT-R.

http://www.nismo.co.jp/GT-R/package/chassis.html

As for comparing spring rates front and rear, you can't really do that since you don't know the motion ratios of the suspension. The wheel rate (WR) which is what you care about is given by the motion ratio (MR) squared times the spring rate (SR).

WR = SR*MR^2

Thus a very small difference in motion ratio can make a big difference in wheel rate which is what the tire and thus handling cares about. You can however compare springs to each other for the same car on the same axle since the motion ratio doesn't change and a 20 % increase in spring rate equals a 20% increase in wheel rate at that tire/axle.

The Cobb suspension seems to take a very different tactic where they soften the fronts compared to OEM and stiffen the rears. AT 700 lbs front and 600 lbs rear, they are really changing the front to rear ratio. Perhaps their setup needs to be used with their bars as a complete package.
 
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