Spring Rate
Test Results for 2006-11 Civic Spring Kits
by Chris Shenefield, RedShift Motorsports - UPDATED 9/10/11
RedShift's Recommendation as a result
of this testing:
Best Slight Drop Springs: HFP (Honda
Factory Performance)
Best Medium Drop Springs: Swift Sport
Best Performance Springs: Neuspeed Sport
Best Slammed Springs: Neuspeed Race
Springs Tested:
1) Stock Civic Si
2) Civic Si HFP
3) Eibach Prokit
4) Swift Sport
5) Eibach Sportline
6) Skunk2 Lowering
7) Progress Sport
8) Neuspeed Sport
9) Neuspeed Race
10) KW V3 coilover
Test rig:
It uses a basic press and is quite manual,
but we are using $900 professional force meter; so
the data is accurate and repeatable. The strut used has been drained
of all oil and no bump stop is used; so the spring is kept securely in place
but only the spring provides force.
Front Swift Sport spring uncompressed. |
Front Swift Sport spring partially compressed. |
Rear Swift spring uncompressed. Rear springs
were tested using the front strut rig and alternate perches. |
Front Neuspeed spring uncompressed. Note the
difference in progressive coil application (in the middle) as
compared to the Swift springs at left. |
Front Eibach Prokit fully compressed. These
springs definitely hit coil bind earlier than any of the others. |
This is the top mount. It's a custom welded
setup that is securely fastened to the press and the strut's top
mount. |
The force gauge is analog but high quality; so the
results are accurate. Note the ball bearing that provides
consistent force application to the gauge. |
Now on with the information..... interesting stuff.
DATA:
| This is total
compression force in lbs. This is the raw data. |
 |
| This is incremental
spring rate in lb/in. This is the "Spring Rate", and it is
derived from the raw data above. |
 |
Front springs.... y-axis is lb/in.:
A few important observations on the
front springs:
1) This front spring data shows an interesting
difference between the Stock/HFP springs and the other "drop" springs in
that the stock and HFP springs are more linear. This is attributable
to the drop springs needing to lower the car; in other words, the first few
inches of compression must be softer to lower the car. The Neuspeed
Sport, Swift Sport, and Neuspeed Race are the most linear of the drop
springs.
2) Prokit, Sportline, and Skunk2 all bind
early..... essentially at coil bind before 7" of
compression where all the others go beyond 7" of compression, but I don't
know how big a concern that is.
3) Related to item #2 above, there is a very
non-linear increase in spring rate of the Prokit, Sportline, Skunk2, and
Progress springs deep into their compression. This could be designed
into the springs, but the reality is that they will feel harsh under heavy
compression (big bumps).
4) The KW V3 front spring is a higher rate, which
I would expect from a coilover type setup, but it's not overly stiff and
should be a very nice street coilover setup.
Rear springs....y-axis is lb/in.:
Each rear tire has 560 lbs on it, and that does not equate to spring
compression force exactly because the spring is far inboard of the wheel
(any wheel force is multiplied at the spring). The distance on the
lower control arm from the inner pivot to the spring is 12 inches, and the
distance from inner pivot to wheel/tire contact patch "vector" is 21 inches.
This means that a wheel force must be multiplied by 21/12 to equal the force
at the spring; so 560 lbs at the wheel is 980 lbs at the spring. 980
lbs is a between 4 and 5 inches on most of these springs (See raw data). The KW V3 is
obviously higher, which makes sense because it is a coilover type setup, but
it is interesting that the Neuspeed Sport springs "primary" coils are in the
same range as the KW V3.
A few important observations on the rear
springs:
1) As with the front springs, the Prokit,
Sportline and Skunk2 all had binding issues and could not be measured to 6"
of compression. And again the Stock and HFP springs are ultra linear
(very nice!).
2) Stock springs and Swift springs are very
similar in back. Prokits are very similar to HFP. Sporline and
Progress are similar rear rates at static ride height. Skunk2 is
higher than all but Neuspeed Sport and Race, which are in a class of their
own. Neuspeed Sport has a more linear performance in the primary coils
than the Neuspeed Race. The Neuspeed Race have the most drop of any
spring; so the spring rate increase may be related to keeping the car from
bottoming out as easily, which the Neuspeed Sport doesn't have to worry
about so much.
Conclusion
So, what does all this mean? Listed below
approximately from from least to most drop, our findings are as follows:
The HFP springs seems to be a very nice
subtle drop option, and they can be had for roughly half the cost of a good
set of shocks and springs; so for the budget minded that don't want to be
slammed and don't need the best performance, they are a great choice.
But they only drop about 1/2"; so it's not super low or super good handling
setup.... but still a very good budget setup.
Our favorite mild drop
springs are the Swift Sport spring. While the Eibach Prokit and Swift
Sport springs are very similar, there is definitely an issue in my mind
with the Prokit binding early in it's compression stroke on the front and
back. Before this test I recommended the Prokit, but now I cannot
recommend it. The Swift Sport is then the only 1" drop spring that I
can recommend. Also, the Swift springs are significantly lighter than
the Eibach Prokit (Prokit = 27.5 lbs and Swift = 21.5 lbs!!).
The Progress Sport springs are a good
spring. In fact, it represents a nice spring which sits in between the
Swift Sport (1" drop) and the Neuspeed Sport (1.6" drop). The Progress
springs offer an advertised 1.3"F1.2"R drop with a spring rate roughly in
between the Swifts and Neuspeed Sports.... a good option.
The Skunk2 Lowering springs are very
Eibach-like in my mind, and they may be made by Eibach. What is most
noticeable is that the Skunk2 springs have the same "coil-bind"
characteristics as the Prokit and Sportline, which none of the other springs
have. I would stay away from these Skunk2 springs for this reason... I
don't recommend the Eibach Prokit or Sportlines either.
Our
favorite performance drop spring
are the Neuspeed Sport
spring. It has a front rate similar to the Swift springs,
but the rear rate at anything beyond static compression (how the car sits at
a stop) is far more appropriate for a performance application than the
Swifts. Also, the Neuspeed springs
don't have any coil bind issues. And lastly, the price is right.
This is what I would put on my car if I had an 06 Civic because I am a
father but also a performance enthusiast who likes to have some fun, and the
Neuspeed Sport springs are far from harsh but will make the car faster
through the turns. Definitely a shock upgrade is necessary with these
springs.... or if you don't do the shock upgrade when you install these,
you'll need them within a few months or your be bitching about how bouncy
your car is because the stock shocks are toast.
The Eibach Sportline sits higher in back
then front and binds under heavy compression. We don't recommend this
spring at all. If anything, the front should sit a bit higher than the
rear because, in our experience developing FWD racecars, it's better to not
lower the front as much as the rear. Why? Because 1) you want
more
more "compliance" (softer) in front for better grip because the
fronts do both turning and accelerating and 2) because lowering either end
of the car causes that end of the car to loose grip in turns faster due to
"roll couple", which is the distance between the center of gravity and the
roll center.....complicated stuff, but slammed in front is not good and why
do that and keep the rear higher....doesn't make any sense. And several have said it looks a bit strange that way...
like a RWD muscle car. Not recommended.
The Neuspeed Race have the most drop of
any spring (2.0"). Even so, the spring rates are not so high that you
will rattle your teeth. Still, an upgrade shock would be important
with these so that you don't go bouncy bouncy down the road.
The KW V3 uses a good spring choice for a coilover on a street car, but they
are a little bit softer than I like for track.... which makes sense because
they the V3 is meant to be a street coilover system... and it does that very
well.
Incidentally, we offer a conversion kit to allow these to run linear race
springs and camber plates for those track-minded drivers; so they are
upgradeable to higher spring rates and camber plates now if needed.
Here are some graphs of the same data listed
above, but these separate the aggressive springs from the less aggressive
springs. And these can be easier to read.
|
Stock, HFP, Prokit, Swift:
FRONT
REAR
|
|
Neuspeed Sport, Progress, Sportline,
Skunk2, Neuspeed Race:
FRONT
REAR
|
Reference info:
Edmunds.com has the 2006 Civic Si listed at 2877 lbs. Weight
distribution is 61% Front and 39% rear..... so, that in pounds is 1755/1122,
or 880 lbs per front tire and 560 lbs per rear tire.
