GBX

I've been speaking with a aircooled suspension specialist about tightening up my setup. One interesting note was that, while they love KW's, they feel the spring rates are mismatched at 30nm/80nm (170lbs/455lbs). They're recommending upping the front a bit to 50nm and keeping the rear as is at 80nm. This part is a bit over my head but it was explained to me that bringing the spring rates closer together will cancel out the front axle frequency and the rear axle frequency. This will result in a smoother ride and reduce porpoise-ing. At first glance, it may seem counter-intuitive so i'm curious to get other's thoughts on this comment since i dont quite understand the science behind it.

Bill Verburg

You can look at either ride frequency or spring rate, they are both describing how the car will handle

the frequency is a more accurate measure but also harder to figure as you need to know the weight on the front wheels and the wheel rate that a given spring provides. I went through the calculations for 911s w/ t-bar suspension but haven't for 993. Basically as the delta in spring rate f/r decreases the delta in ride frequency also decreases and the oversteer increases or under steer decreases depending on how you want to look at it.

Long story short spring rates delta is easier to look at and describes as well behavior from various springs


KW does have a lot of rear spring w/ a spring rate delta of 285

Most track oriented 993 will have a Δ more like 150

so what you would be looking for w/ 455 rears is 305 front
track cars will use higher overall but keep the delta so 600/750 600/800(more oversteer) up to 1142/1256(even more over steer)

RS used a very conservative 246/457

k722070

there's quite a bit on spring rates, one recent thread where a bunch of ratios were posted by jstyer
https://rennlist.com/forums/racing-a...oversteer.html

here's an older thread with rates posted
https://rennlist.com/forums/993-foru...ing-rates.html

your car be shouldn't porpoise-ing, comparing the ratios posted to your current would indicate the shop has a good idea about changing the front spring rate.

Tuner1

I've done this on three sets of KW V3s (964 C2, 993TT and 964T) and the end result was positive. I liked the overall handling balance and the additional front spring rate allowed me to run a lower front ride height would blowing through the bump travel as quickly.

The 993TT with this set-up on Hoosiers had lots of grip

Bill Verburg

Here is the ride frequency data for a ~2900# 993
sedans generally are closer to 1Hz, sportscars closer to 2Hz, you want front to be a bit higher than rear, the data for the street cars is probably not as accurate as for the track cars due to the dual rate springs they use, that confuses the issue more than I care to get involved w/


As I said if you just look at the raw spring rates(col 3) and get a delta of ~150 to 200 +/- and you are good to go

GBX

So, it sounds like 50nm/80nm or 285lb/455lb is a better match. Why do we think Kw builds their coil over with such large deltas in their spring sets?

GBX

Bringing back this thread. Picking up a 964 Targa and want to do something similar. Does the 150 delta hold true on the 964s or is it a whole different animal with the different rear suspension setup?

CAGCTG

Since GBX brought back this thread, I thought I would post my recent (novice) experience on my 993. I had Adam Gill at Vollig Automotive install a Bilstein PSS10 suspension with new sport bushings, drop links front and rear, and stabilizers. I have set it on a "comfort" setting of 2 out of 10. The cornering and stability are a whole new dimension from the stock US suspension. Turn-in is quick, and the rear is just planted, I have yet to feel the rear start to get light. The cornering is beautiful to behold. The trade-off is the car feels every bump in the road. I've gotten used to it, and greatly appreciate the stability and improved cornering speeds. Oh, and the lowered stance is beauty.

Bill Verburg

(64 seems to be all over the place, i don't know if thats form poor data or what, the following are spring rates not wheel rates as I have for 91 and 993 so no direct comparison is possible
Base 964 C2 seems to be 169/189lb/in Δ20
M030 200/275lb/in Δ75
RS 308/508lb/inΔ200
Cup 600/800lb/inΔ200
H&R green 255/265lb/in Δ10
H&R Red 270/285lb/inΔ15
H&R Cup 455/685lb/in Δ230
H&R performance street 500/780b/in Δ280
Eibach Pro 6 250/256b/in Δ6
PSS9 250/685b/in Δ435

as always the more delta the less understeer

the higher the rate the harsher the ride, though shock valving and bushes and tires have a large effect here too

aam993

Bill do you know part numbers for Cup springs/struts?

I assume 964-343-531-80/993-333-531-81 is the part number for the front/rear RS springs (to match 964-343-041/042-80, 993-333-051-80 RS struts).

Bill Verburg

'92 964 Cup
front 964.343.533.70 x2

rear 964.333.533.70 x2

aam993

Ah, 964 Cup, got you, thanks. Didn't realize it was applicable to 993.

Do you know what 993 gt2/rsr suspension might be? fvd has front/rear "993 gt2/rsr" shocks https://www.fvd.net/us-en/115343097/...ft-140-80.html

Bill Verburg

It's not except possibly the fronts'

993gt2evo, no one wants these, way to stiff for anyone I know
front yellow 1542lb/in
rear
red 1690lb/in
blue 1342 lb/in
white 1622lb/in

993RSR or these
F1342lb/in R1542lb/in
optional F1622lb/in 1R690lb/in

993Cup, still way too stiff
F1142lb/in R1256lb/in

MarinS4

Makes you wonder about tire technologies back in the day if that’s the spring rates they ran.

Historical data can certainly be helpful but with all of the tire and shock changes to date it’s probably best to get a spring baseline from another local racer.

Bill do you know of anyone running those crazy high spring rates these days?