AudiOn19s

I don't want to de-rail this thread, but this is a topic I think about often and constantly hear differing views on. I'd love to hear more on your experiences.

Are you basing the judgement that 1400/1500 is better based on peak G numbers only? You state you were "overpowering" the car on 700/900 but not with the 1400/1500...is this just power-on oversteer you are referring to?

Are your lap times better on the 1400/1500 setup, are your vMin speeds in corners higher than they were with the softer springs. Is the driveability of the car better everywhere?

My understanding is that spring rate is very much tire dependent. It takes me back to my motorcycle days where contact patch management and understanding of how the contact patches are loaded is VERY important. The harder the tire the easier it is to overload the tire and cause it to have great traction one moment and then completely break way the next due to too much load and the inability of the suspension and tire to cope with the quick load change. Conversely too soft will do the same thing it's just a much more gradual slope to the break away point. With stoft / sticky rubber the issue becomes keeping the geometry of the suspension in check and stiffness here keeps from too much suspension movement and keeping everything in ideal ranges. The criticality as I understand it is finding a balance between tire and spring rate that allows them to work in unison.

Another data point to add is my shock guy feels that even my 600/750 setup in my car might be too much for the tires I'm running. He has tuned shocks / suspension on Indy 500 winning race cars and says the most common thing he sees when he comes into a fresh team to start working with them is they are almost always running too much spring rate and nitrogen pressure in their shocks. Almost always the first thing he does is take down the rate and take down canister pressures for their first test session.

Again...I don't have first hand data of my own...without tooting my own horn my car is pretty darn quick on nitto's but I'm always looking for ways to improve. I've just not seen enough hard data to sway me into going through the efforts of swapping springs to date. One thing I did notice this year is I tried playing around with nitrogen pressures to emulate spring change and did like the way the car felt when I added rear nitrogen pressure as an experiment.

rbahr

Hi All,

Been going through a bit of this myself.

Suspension setup for me is complete monoball, RSR bits, Moton 2 way, 175psi for shock preassure, 1200/1000 spring rates, Nitto's with slicks sitting in the corner

Corner weighted the car, ballparked some motion ratios and ran the numbers and got ~600/800 for spring rates.

I was convinced that the spring rate would have been terrible, have put ~600 track miles on the car and the spring rate feels very compliant on the track. I am not crashing around or doing bad things. That said I cannot hit burms without the car getting a bit upset...

I had been planning to drop to 700/900 but I am just not sure at this point, it actually fees pretty good.

I have some tattletales on the shocks from my last event, and don't quite know how much travel I have - will find out

I know that I am pulling some serious g's >1.5 in some of the sweepers with the car - I still need to look at the data...

I suspect that a lot has to do with the ride height, ( where you are on the camber curve in steady state), because the street GT3 suspension starts getting pretty fuggley (tech term :-) ) when it gets much lower than stock, and if you are to low and you constrain movement with heavy springs it 'seems' to help - kind like Colin Chapman reportedly once said, “Any suspension will work if you don’t let it.”

Ray

kk2

Ray.. your car is far from typical.

utkinpol

most of this stuff is an empirical knowledge of racers and builders.

you have 2 options, essentially. if you no longer interested to drive this car on a street - strip it, do a full cage, then try to use as many parts and specs to turn this car into a 996 cup. there is no need to reinvent a bicycle - look up spring rates of a cup, rake setup, ride height and copy it.

be aware that a cup mostly goes on a rubber (tires) flex, low sitting stiff springs setup absolutely requires proper aero setup as well, you will need to put on proper front cup bumper/splitter and proper rear wing. Also, I do highly recommend you to ask for a ride in a cup car when owner (preferably) will try to drive it for a re-fuel to a pump so you could experience yourself how it goes over a public road. but if it is a track only car, then it is a best path anyway.

If you intend to keep it as it was before - a dual use car, then you will be using NT01 tires or RA1 - for those I do think 700-900 rates are somewhat optimal and it is still drivable this way - just put for street driving compression to 2 clicks from softest and rebound to 4-5.

cfjan

While it would be an absolutely cool to do a "street legal Cup", I am honest with my intended usage: I don't see myself having a tow rig in the near future and will continue to keep the car street legal and drive to tracks and autocross. And now and then, take the car out for a spin, etc. I plan to run mostly NT-01s. I have had pretty good luck with it.

The car has mostly monoballs now, so damper/springs are pretty much the last piece of the puzzle. I am not too concerned about street comfort. Initially I suggested to the shop that given my use, should I stick with the 700/900 that's found on Spec 996 class. Those cars are lighter, but run stickier tires, while GT3 has more power and more brake. I was thinking maybe it would be a wash. The shop that's doing the setup told me that they recommend me using 600/800 (with 125 tender springs) instead. The shop is a JRZ authorized dealer and support many race cars, I am counting on them knowing what's a good setup.

powdrhound

To answer your questions, no I'm not basing it no peak G numbers. Like I said, I've run 600/800, 700/800, 1100/1200, and now 1400/1500. Lap times are quickest with the 1400/1500 set up mainly due to the fact that the car with 1400/1500 is more precise in steering input and is quicker in switch back transitions without upsetting the chassis. In other words, it is much quicker in sections of the track where you are going though either fast or slow S turns because the car stays more planted and doesn't wallow from side to side during aggressive steering inputs. The car transitions quicker if that makes sense and it's much easier to place with precision. More of a scalper rather than a butter knife if you will. I will preface this by saying that in my opinion, if you are going to run Cup spring rates, you will need to remove all the rubber from the suspension in order to reap the benefits. It goes without saying you can't just stiff springs with the OEM shocks. You will obviously also need to run a Motorsport quality shock designed for such high rates.

I did not say I was overpowering the car, I said I was "overpowering" the springs when I ran the much softer rates. I other words, the suspension felt really squishy when under load and the car would take bit longer to settle down exiting turns for example . All of this was reduced with the stiffer set up taking away a tenth of a second here, a tenth of a second there. Over a typical lap with 15 turns or so, it adds up. If I can say anything, having the stiffer rates makes it easier for me to drive the car more aggressively as it seems that breakaway is more progressive now. I think this has to do with the fact that the suspension is always closer to the "sweetspot" and composed at the limit as opposed to before when you would have the car leaning much more when traction began to give way.

I have not found any issues running the stiffer rates with tires like NT01s and V710 (which are similar to Hoosiers). I am running camber at -3.4º camber front and -2.5º rear. Tire are NT01 245/40/18 and 305/35/18 or Kumho 245/40/18 and 315/35/18. I have GT3 sways. Front is on the middle hole (3 out of 5) and rear is 1 from full soft (3 out of 4). Ride height is 96mm front, 120mm rear. Canister nitrogen pressure is 175psi front and rear. Front sprigs are 1400# with 150# helpers and rears are 1500# with 250# helpers. The car is still perfectly drivable on the street if the roads are ok. I really don't care about street comfort though and only drive it 2-3 times per month on the street. I daily drive an SUV. The OP said he doesn't really care about street comfort so I take it he was trying to optimize a track set up.

As another data point, one of your local instructors who is an excellent driver, runs a 6GT3 with all the trimmings. He had Motons with your typical 700/900 rates. After talking with my shop, he ended up getting 996Cup springs/helpers installed on his car. If I recall, the rates on the mains are 240/260NM which is 1370/1484#. He loves it and can't believe how well that set up performs. He posts here from time to time. Sorry, I don't know his before and after lap times. Hope this helps....

mldgman

I was recently in the same boat and thought that powdrhound was nuts recommending the stiffer spring rates and I want with much softer ones and wish I had gone a bit stiffer. Go with stiffer springs!!!

rbahr

I am pretty sure that the cup car springs are as stiff as they are in part to compensate for the not-very-good suspension settings.

That said, the harder you corner and the more aero you have, the more spring you will need. If you use more spring than you need, your suspension will just not be doing anything, this is why this question is driven so much by lore - it is really hard and expensive to quantify everything...

Ray

rbahr

powdrhound :

When you run the car on the track, do you check tire temps? I am curious as to what you see?

In addition you are running ~24mm of rake - I thing the cups run ~13mm

Ray

powdrhound

Ray,
I haven't measured tire temps on my current set up. I'll take some readings next Friday and post some data next week. My hot pressures are 33/34 fwiw.

My rake is a 3mm more than a Cup, so roughly 1/8" more. 6Cup ride night is 86/107, so a 21mm rake vs 24mm on my car. Pretty much the same. I run 25.5"/26.4" tall tires which are comparable to cup sizes where the rear tire is almost 1" taller than the front. Seriously though, the car feels fantastic and is very very fast. It was set up from top to bottom by a local retired professional Cup driver who is by far the fastest and most competent driver in our region. He has set up pretty much every serious GT3 and Cup car in our region. With his set up, the car is turning a 1:55 laps compared to 2:02 before he got his hands on it last fall. Most importantly, it's much easier and more forgiving when the car is pushed hard at the limit which says a lot considering with 600hp was quite a handful before.

AudiOn19s

Good stuff. Thank you for sharing

rbahr

This is all great information - thanks.

The physics of the matter is that the more lateral accel you generate (eg the faster you go due to tires/power/whatever) the more roll you will have and the more important it will be to keep the suspension in the sweet spot.

Right now I am running out of shock travel in the rear - measured it last night - I have ~1" on the Motons and I have 1200lb springs, I too, amd seeing 1.5g's or more at least in a somewhat dynamic manner. The interesting thing is that I am on the rear bumpstops and the car feels great, this implies that the spring rate (for me) is non-linear - when I hit the stops, the spring rate jumps - this may imply that I can easily handle high spring rates, and this is with Nitto's. With that said I do have Aero which adds to the matter.

BTW - I apologize if this thread is being hyjacked - but this is all great info...

Ray

cfjan

No worry about the spring rate discussion, as that's what I am interested in as well!

rbahr

Great,

In that case a VERY important point - spring rates are related to your skill level and driving style and suspension (including tires) - like everything this is a big trade space.

If you push the car hard, run slicks or maybe R compounds, and you are a smooth driver bigger is better, if you are say an intermediate driver than perhaps go lighter. (sorry - the type of track surface is also important)

To TRY and put numbers on this (worth exactly what you are paying for) - keep a 200-300 lb difference front to rear, Advanced is probably (rear) 1200 to perhaps in the 2K-3K range, intermediate is probably in say 900-1200 range, beginner is likely in the stock - 900 range...

NOTE: This is a COMPLETE SWAG.... but to put a line in the sand - and perhaps get more discussion....

Ray

cfjan

Yes, still just an intermediate level driver (white run group with CVR PCA), runs Nitto NT-01, drive to track, no trailer, but street comfort is not really a concern. Initially I proposed 700/900, but the shop recommended me to go with 600/800 instead.

I guess I can try the setup for a couple of years, and when the shocks needs to be re-built, I can up the spring rate by then, if needed..