rbahr

ALL supposition:

I don't disagree that you are getting better times - just saying that this is because you have a good static setup and your high spring rate prevents things from changing much.

I would love to understand what you are getting for suspension travel - have you ever measured it?

Ray

powdrhound

I have roughly 2" of droop from static ride height. The main springs have about 2.5" of possible travel before coil bind. Thus, there about 4" of total shock travel possible. How much suspension travel do I have under track use? I have no idea, probably half that taking the spring rates into account.

Based on having run much softer rates before, I can tell you that the car is much more responsive with my current 1400/1500 springs. Steering inputs are more direct and the car is quicker through fast left/right transitions as there is much less body roll. It's much easier to drive the car at the limit as the chassis is composed and stays closer to it's sweet spot that with the soft rates which allowed more body roll, dive and squat. Since there is much less body roll, naturally any bump steer is minimized. I don't feel that I'm giving up anything at all even on the bumpier sections of the track. I do feel that in order to run these kind of rate you really need to monoball the whole the suspension to keep everything in check.

rbahr

Ok,

If you have time and the inclination, before your next track day,put zip-ties on the shock shafts, let the car settle and note where they end up in a static sense, go out and drive it hard and then note where they end up...

Thanks

Ray

Kaizu

rbahr, I am no pro here, just stating how with spring rates it's a never ending discussion. So many different ways to skin a cat!

I haven't been yet a fan of high spring rates* while powdrhound and some others have very fast cars with those. On the other side, didn't user 930man had higher rates in front and a soft rear with his fast 996GT2

Whole setup seem to affect the choice of spring rate. Obvious ones are tires, shock setup, weight, aero etc. But I would put a lot of focus on rake and suspension height as well as the sway bar setup. Those really affects this!

*Actually, I kind of like the idea of going to high spring rates and loose sway bars...

Different tracks can require different springs as well if you are pushing to the limit. Stating Cup rates as xxx can be misleading as their springs depends on the track. I know personally street-registered cars that get springs changed depending on the track when driven to the very maximum.

In a recent talk with a team in international Porsche racing, they actually liked how they can decrease the spring rates due to high-quality shocks. Their master mechanic saw that as a trend...like how some GT3R's and RSR's opt for softer springs for better grip.

However, seen many times how a spring rate setup recommended either by the internet gods here, or a reputable Porsche racing team hasn't ended up to be the optimal choice.

Many things affect this, so trial and error is the way to go You can be fast with different setups, great that we share info here

P.S. powdrhound, I got the Brembo GT's finally performing okayish, so not going to PCCB calendars at the moment. Many thanks for your big help again there. In terms of shopping, what I found annoying but funny is that my neighbor(!) was faster and could buy 911SLOW's full set of carbon fibre body parts at a discounted price just before I saw the Rennlist thread. Lesson learned, browse rennlist more often

rbahr

The interesting thing here is that I mostly agree with a lot of what I see. I DO think that my spring rates are to high as when I hit turtles esp with the high canister pressure the car bounces - could also be because I am hitting the bump stops (measured it). The interesting thing here is that while I was on the bump stops the car did not feel bad - no big surprises - and the spring-rate there... It makes me think that it can get a lot better...

I agree that rake, sway bar settings, ride height, etc are all very important and I am at that point where the suspension bits are essentially as good as it gets, just need to get some seat time learn to drive the car, and also some advice from smart people on how to tune things. I KNOW that there is easily 5-10 seconds left in the car... Lessons for next summer :-)

Couple of things: The cup car suspension and the GT3 street suspension are nearly identical - spring rates, ride height, shocks are different, but all the various locating parts are essentially the same. This all leads me to thing that the cup car suspension is running at a sub-optimal point...

My previous track car was a Subaru STi which was pretty quick, and weighed more than the GT3 had much lighter springs but I was also running good shocks - Ohlins and I was happy with that setup. Car did exactly what I wanted...

Ray

pete95zhn

Few comments, just my own without any significant expertice...just what I've read or learnt during last few years I've been involved these squashed beetles. Somehow a 951 was much easier, a lot less variables there.

Rake. From big boys' experiences it's very important for front end (aero)grip. Different chassis/subframe combinations get it different ways and tire diameters affect it directly.

Bump stops. They seem to be an organic part of 99x's suspension dynamics. Panorama had a article about 996 Carrera's different suspensions and each of the had it's own bump stop, with unique characteristics, supporting the main spring near full compression. Also GT3's, Cups and even RSR's have their own ones...

Suspension height/movement. In combination with correct springs one gets a setup where there's enough movement in both compression and rebound. If the spring rate is modest, this can be achieved with one spring of correct lenght. Then it'll unwind to full droop without going loose and compress fully without coils touching. (Maybe with a help of a bump stop.) Anyway shock works as designed and has required (but maybe not equal) movement both directions.
When using stiff (race) springs helpers must be used. Then the full droop (and tire contact to track) is achieved with helpers. Which usually are more or less totally compressed when car's stationary. Then the main spring barely compresses. Well, if the spring rate is 260 N/mm and axle load is 800 kg (8000 N or 4000 N / spring) the spring compresses just 15mm (Cup's rear in example). If shock's free movement is 120 mm minus the bump stop (like 40mm or maybe 20 mm fully compressed), there's 100 mm of movement. If one wants to center the shock when car's not moving (1G vertical), then the total compression (and also the rebound) of the helper and main is 50 mm. 15 mm from the main and 35 from fully compressed helper. Then there's still 50 mm of compression available, whichof 30 mm with out the bump stop. 2G's vertical compresses the spring additional 15mm and 3G's 15mm more...and then the bump stop starts to work too.
My rear suspension was not set properly before this spring (by mostly my own fault) and there was not enough rebound length available from the shock and limited compression from the spring. That caused some weird issues at bumpy tracks. Now that springs are correctly set to allow full shock movement there's no problems. Even though my spring rates are still modest compared to some. F 80 N/mm, R 120 N/mm. Balanced though and I can't say they've bottomed, not even at the bottom of the Fuchsröhre, but my slow speed may affect that too... I still might switch to slightly stiffer ones, like 100 / 150 N/mm.

Sway bars. What I've read, they should be used only for fine tuning. So loose bars there.

Spring rate fine tuning. Race cars have it better. See the pic below, look at the silver thingy at the top of the main spring. By turning that the spring rate can be adjusted. I only have data for '02 GT3RS (FIA/ACO), but there the range is either F: 282-345 N/mm and R: 304-356 or 317-375 N/mm, depending on the spring used.




The car in the pic is a GT3 -class Z4.

To convert N/mm to lb/in multiply with 5.709.

FFaust

Can I ask what tires you run? Or if you prefer, do you run slicks?

I currently have 950/1050 but have a set of stiffer springs that I could try.

powdrhound

245/40/18 + 305/35/18 NT01s or 245/40/18 + 315/35/18 V710s. The V710s are basically on par with an R6. Slicks would be great for a few hero sessions but I'm very hard on tires and slicks would rape the tire budget. I get about 17-18 sessions on the NT01s and half that on the 710s.

FFaust

Thanks.

I have a set of 1100/1300 that maybe I'll try... for fun, to see how that feels.

I thought that, for such stiff springs, you would need stickier tires, but I guess not