Originally Posted by Steve Jarvis (Post 3835115)

As you mention in the lower section of your post, pro cup cars run these spring rates and higher, but they don't put out nearly the torque of a modified TT and they use a different swaybar setup to get the needed balance (usually adjustable blade type bars).

My belief is with our turbo cars, we need run lower spring rates (800 or less) and use the bars to better tune the balance.

Later, Steve

Originally Posted by Steve Jarvis (Post 3835106)

Heavychevy,

See my comments below.



Great information. I like to include data in a discussion like this, because handling balance can be very subjective. A lot of people have no idea if their car understeers/oversteers due to the basic balance or because of their inputs. Even if they have a feel for that, they can easily mistake their balance under trail braking and on throttle to be the steady state balance of the car. As you have stated well below, the handling balance of these cars changes even more due to the rear weight bias and AWD.



Very interesting, since my assumption is a larger gap in spring rates front to rear (assuming the rear spring rate is higher than the front) will cause more oversteer. The higher rear spring rate will not allow the rear to compress as much as the front when rolling (laterally) into a corner, keeping more weight on the front tires and giving the front tires more grip. When I drove a 997 GT3 RS, it was way more neutral than my car and it had 228 front and 600 rear springs. I know the suspension geometry and track are different on the 997 GT3 RS, but that was an almost 400 pound difference and the car didn't oversteer at all. 996TWINS only has a 286 pound difference front/rear.

Of course everything changes as you begin to accelerate out of the turn, and that may be were higher rear spring rates really shine as they reduce squat keeping more weight on the front tires. Not the best for putting turbo power to the ground, but much better for reducing on throttle understeer.



I think you're really on to something with this statement. I find it strange how the front end will "pogo" in these cars. As you stated above, it is probably a "See Saw" affect where our rear tires become the fulcrum point and the engine is the counter weight. I wonder if more rebound dampening would improve this tendancy?



For your stiffer setup, I would agree, but for a softer setup like mine, the opposite may work better.
- Stiffen the rear sway
- Stiffen the rear springs
- Stiffen the rear compression/rebound



Agree



I agree, but his setup doesn't appear like it should be causing too much oversteer, that's why I think he has a different issue. I could easily see why his high rear spring rate would cause the car to oversteer on power as high spring rate won't transfer weight to the rear tires.

It could be that my spring rates are very low (260/515) and that is why they don't cause the same dynamics that occur with higher rates, but with a 255 pound variance front to rear, my car definitely understeers under steady state cornering.

Good discussion, thanks for sharing.

Later, Steve

Originally Posted by heavychevy (Post 3835575)

800 lbs is about as stiff as you can make use of on DOT treaded tires.

Originally Posted by heavychevy (Post 3835575)

I
Anything less than that and I agree with you. 800 lbs is about as stiff as you can make use of on DOT treaded tires. Of course some guys like loose cars (F1crazydriver) and want it to dance all over the place, so for them, the heavier rates might work.
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Originally Posted by MrWhite (Post 3838259)

Before giving advise I will just mention that SoW incl bowl config I ran 1.21 as a reference w KW V3 on Hankook RS3 street tires (not R-comp like R888) w K16 turbos, PSM has to be disconnected though to do that and you need -3.5 rear camber and at least -2.8 front for the tires to cope with it.

Step one to fix your issue: Drop rear rideheight (1/8 in increments) and it calms down A LOT, and it adds rear negative camber at the same time which you need. The positive rake creates excessive twitchiness and both 996 and 997 are extremely sensitive to this. It also creates a very hard to solve oversteer issue, so this is the first job or you can go on forever to find a "band aid" fix.

In addition, rear camber should be at least -3 degrees (not ideal for street, I know, but it helps to go fast), and make sure you have at least 5mm (1/4in) total rear toe-in.

As mentioned above you can reduce a 10-15 percent on rear compression if you still feel that the rear tires are not "biting" and only "skidding" on top of the surface. But if you feel the tires are in fact biting and the chassis is just oversteered, the key to treat especially corner exit oversteer is to tighten the front rebound slightly and it will balance this.

Instead of swaybar swapping I recommend a set of adjustable Eibach Racing swaybars. They will put you in the exact ballpark adjustment you need and is then quick to adjust at the track given the conditions and overall setup. Best "speed for money" there is on these cars.

Your goal is to have a car that comes around perfect when you add all the power there is. If you don't add all power bc you missed the line or got on the gas late, it should have a slight slight push. Into turns, the car should also have a minimal push, so you can brake later and trailbrake all the way to apex and rotate the car that way (using weight transfer rather than steering).

Foot note: I am a "hot shoe" for hire and I always do engineering by means of data logging and measuring tire temps to get the right setup for any car (with 911 racecars being my absolute expertise), and coaching includes not just saying "brake here, apex there" but work to transfer the entire mindset needed to self coach and understand the chassis you are driving.

Originally Posted by 996TWINS (Post 3837664)

Heavy, went to my shop tonight and we went over how the car responds in corner entry, mid corner , and corner exit in great detail. You are correct on the above statement in reference to the rear spring rate. Not the front as I thought.

So the rear spring rate will be changed to about 850 lbs/in (857 lbs/in according to the specs) and the front will remain unchanged at 685lbs/in. So the difference will be 172lbs/in. Below the 200 lbs/in threshold.

After this, finally get going to the track. Cannot believe it is already May!!! 5/12 ths of the season is gone :(

Thank you all for your input.

Originally Posted by MrWhite (Post 3839163)

In the name of interesting topics, here's a graph to show an example of a typical datalog speed trace seen between the typical fast guy vs a pro. The fast guys usually burn up their front tire edges quicker, due to spending longer time mid corner with more steering lock to drive around the turn (data logging of steering angle sensors show this difference as well between drivers A and B). As f1 mentioned, it's harder on the rear tires too bc more slip on exit.

https://www.6speedonline.com/forums/...ictureid=29931

What you see here is that the pro (black line) towards the end turns into the turn while carrying speed almost into apex, whereas the fast guy slows down until it's time to turn, then turns and goes to throttle. The pro is essentially on the brake until the car has pivoted and then the pro gets back on throttle very hard with the car in the right direction. The blue driver has to "negotiate the turn" for a while before exiting. The "negotiation" of the turn takes time and if the car is not perfectly neutral or willing to self turn (slight oversteer) it feels like AN ETERNITY, so at this time a slightly more oversteered setup will absolutely help this guy turn faster laps unless changing the driving style.

The red zone is speed x time = translates into distance won/lost and in the end means laptime. Data graphs with these corner entries are probably the ones I have seen most in my career between tru pros vs non pro drivers. In a typical corner it generates a time difference of appr 1-2 tenths of a sec. Add up a number of turns and you find a chunk of lap time that separates the pro vs any very fast guy.

This is one of the hardest things to learn to do consistently as a driver without flying off the track or missing apexes, or overbraking. Pro drivers excel at this type of stuff. Karting is great training for it.

Also worth to mention, let's say crazy is driving the car already like a pro, then he will feel that the car is neutral and almost a little oversteered and pivots by weight transfer. If you add push in that moment, when the driver is already at true true 100% , well, he can't pivot the car anymore using an aggressive corner entry.

So, in the end, finding a good setup balance for your taste, and then using a datalogger in the car that can collect at least speed and lat acc (video is a great bonus), you can go back "self coach" your way to better driving and a better setup, you only have to know what to look for. :)

Now onto a nice Friday afternoon /eve , have fun those of you that are hitting the track this weekend!

Originally Posted by heavychevy (Post 3839101)

Great, let us know how it goes! Post some pics, video, anything. This place needs some interesting threads not involving street, drag, roll racing.

Originally Posted by silver (Post 3840035)

I did not read all the posts completely but my suggestion is this you should be set to full stiff or nearly full stiff in rear and full soft in front for the bars. Spring rates are better for someone else to answer. I have PSS9 and used to track at full stiff on the shocks but now I am on 4 front 1 rear and it made the car turn much better. Sorry if someone already stated bar settings but I have had many tell me stiff rear soft front turns better. Stiff rear can probably still run factorty front. Good luck.

Originally Posted by MrWhite (Post 3838259)

Before giving advise I will just mention that SoW incl bowl config I ran 1.21 as a reference w KW V3 on Hankook RS3...