Excellent post and very interesting data - thanks for the effort.

FWIW, spring rates for 997.1 Turbo's Bilstein B16 Damptronic are 336 front, 560 rear. I am currently running mine at 448 front/ 560 rear, using 70mm ID, 6 inch springs from http://www.swiftsprings.net/file/metric.pdf , and I absolutely love it. The stiffer front spring rates help a lot with making steering firmer and more precise, with no significant increase in understeer. In the 997 Turbo, stock steering is too soft/mushy (over assisted) so this change is very welcome.

 

Vary good info.

 

Thanks for into. My c4 came with PSS9 and I wonder what the rates are compared to stock.

 

Stock spring rates are something like 180 front and 340 rear
ROW 200f & 400r
PSS10/9 260f & 515r

Guesstimate from Pwrdhound.
http://rennlist.com/forums/996-turbo...l-overs-4.html
"ROW is generally a bit lower and stiffer than the Stock suspension. My guess is 10-15% stiffer. Stock spring rates are something like 180 front and 340 rear which would make ROW 200/400, give or take. The H&R street coil over kit is 260 front (linear) and around 500 rear (progressive). There is really no way to quote an exact number for a progressive spring. Race springs will be linear by the way.. Cheers... "

 

Just installed Swift Springs on 07 Porsche Turbo over Bilstein B16 with
Damptronics. Springs rates of 560F and 770R.

A little about the car:
*Original sways front and rear.
*Ride height 136R / 118 F
*Original wheels
*Pirelli P-Zero tires -PSI 34F / 38R
*Rennline solid motor mounts.

A little about road conditions: Testing was performed in typical Ventura county freeways and roads which I would rate as better than average California roads. If testing was executed on Los Angeles roads, the outcome would be much harsher, unbearable for driver and possible destruction of shocks.


Newly installed: Springs rates of 560F and 770R.

Impression:

The original valving of the Bilstein shocks are not capable of handling such high spring rates as the ride is extremely bouncy over bumps and freeway overpass transitions. The dampening strength of the shock is not capable of harnessing the load in which the spring creates over bumps.

On extremely smooth roads and curves, the ride feels stable and well planted, confidence inspiring.

Rear- Reduced side to side movement at rear when aggressively taking a long sweeping curve onto a freeway.

Front- No dipping at front when aggressively taking long sweeping curve onto a freeway.

Under/Over Steer - No change from original Bilstein set up.

Squatting is reduced under hard acceleration.

Nose dive is reduced under extreme braking.

Steering feels amazing although a bit heavy for daily driving.

Final thoughts- Not for everyday driving unless roads are smooth.

 

Great thread bumped! One of my favorite mods on my last car with pss9 coil overs was changing the springs. I mostly drive the 996 on the street but subscribed incase I get bored down the road or start driving it!
Shawn

 

So I installed B14/B16s (PN 48-186346) and the rear helper springs are completely compressed even with the rear wheels off the ground The fronts are fine Some travel available in the helpers before going solid unlike the rears. I put 997 turbo wheels and 245/35 305/30 Hankooks on and now sure why the helper on rear is fully compressed Any help appreciated