I have converted my 996tt to RWD along with GT2/3 uprights and even a GT2 gas tank. I have a H&R rear bar but still have the stock 996tt front bar. Would I benefit by going with the front OEM GT2/3 sway bar?

 

Don,
I would not run the H&R rear sway bar with your RWD set up. Been there, done that. The H&R rear sway bar is thick, solid, and extremely stiff even at its softest setting. It will cause you oversteer issues even when mated to the stiffer front GT3 bar. When coupled with the very soft stock front bar the car is downright dangerous with very abrupt snap oversteer mid corner and a real handful under even modest trail braking. I would sell the H&R and get a matching set of front and rear GT3 bars. The rear is 4 way and front is 5 way adjustable. Depending on your spring rates, start the front bar in the middle and rear bar one hole from full soft. This works really well with my 1100/1200 springs. This will set the car up towards mild understeer which will allow you to trail brake hard to initiate rotation. Power on mid corner ovesteer is minimized. If you are running a larger spring gap front to rear, you will want to tighten the front bar more. Hope that helps...

 

pwdrhound,

It's interesting to see your comments. Of course you are running aggressive spring rates, so your experience with the bars may be different than someone with stock springs or a mild PSS10 setup.

I'm currently running PSS10's (260/515 spring rates) with a stock front bar and GT3 rear bar (set to its stiffest setting). The car still has way too much understeer.

The stock wheel rate percent is 55% front and 45% rear, even though the weight distribution is 38% front and 62% rear. This is one of the reasons why the stock setup has so much understeer and such a heavy rear feel (along with the rear diff/awd setup).

My setup with PSS10's and a GT3 rear swaybar has changed the wheel rate to 52% front and 48% rear, but this is still a long way from the weight distribution numbers. Which is why is still understeers too much. I definitely need want the car more free than the current setup. Keep in mind we all have different handling balance preferences and driving styles. I tend to like a car where the rear moves around.

I'm getting ready to install an H&R rear bar with my stock front bar. This will put my wheel rate percent at 41% front and 59% rear. I know my current 48% rear wheel rate distribution is not enough, so my next step is the H&R bar. If I remember correctly, the H&R bar will allow me to change my wheel rate percent from approximately 52% to 59% rear.

For a point of reference, the wheel rate distribution of a 997.2 GT3RS (which is one of the best handling 911's ever) is approximately 38% front and 62% rear. Interestingly almost identical to it's f/r weight distribution. Though we would typically want to achieve those numbers on a turbo with less rear spring rate and more rear bar to maintain the needed weight transfer to put the torque generate by our cars to the ground.

I would expect that any typical swaybar would have a very little small affect on your setup (given the stiffness of your springs). As an example, the stock swaybars would only account for approximately 4% of your total wheel rate. Your setup is definitely different than most 996TT owners and you have several things that would also affect handling balance (especially under braking). Given this, I have a few questions.

Were you running the stock front bar and H&R rear bar with
1. Your current spring setup or with a different setup?
2. Were you running this with the Guard LSD?
3. Were you running this setup with the 380/350 brakes?

Later, Steve

 

Hi Steve,

To answer the above questions:

I ran the stock front sway bar with the rear H&R sway bar set to full soft in the following configurations:

1. H&R street coil overs (similar spring rates to PSS10s) in AWD w/o LSD.
This set up was decent but not very fast. It really did not oversteer under power mainly due to the fact that you could not get the power down effectively with the open diff. It did, however, oversteer quite a bit on turn entry with aggressive trail braking with a nasty tendency to swap ends that was hard to catch. This was largely in part also due to the soft spring which allowed to car to nose dive quite a bit under braking (this is why a square spring set up works so well on these cars). More on that later.

2. H&R street coil overs in AWD with LSD.
This set up was similar to #1 except there as also a nasty tendency to oversteer mid turn and on turn exit due to the fact that so much more power was going to the back wheels now.

Both set up #1 and #2 were run with 996GT3 350/350 brakes which have the same distribution as stock TT brakes. I swapped to the 380/350 997GT3 brakes a few months after installing set up #3. Even though the brakes are much more biased towards the rear I could not tell much of any difference except they worked much better. Balance was unaffected as far as I could tell.

3. JRZ RS1 coil overs with 700/800 springs, RWD, and LSD.
This set up was better than both #1 and #2 largely due to the fact that I no longer had the squishy 260/550 rates of the H&R coil overs but had a much more square 700/800 rates which set the car up for more understeer slightly off setting the stiff rear H&R bar and soft TT front bar. The car however still oversteered with aggressive trail braking and one had to be very cautious with power application mid turn to keep the rear from breaking loose and coming around.

At the time I felt like I had a dialed in car as I thought "slightly loose" was the way to go. Incidentally this is the myth perpetuated on all the forums as all the weekend warriors complain ad nauseum about these cars understeering but it's the same guys that go charging into a turn braking like mad in a straight line, turning the wheel, squeezing the power on as they enter a turn and complaining that the car plows and doesn't turn. Duh!

It wasn't until I had a Pro driver take my car for a spin around the track. After one lap he pulled over stating that the car is deadly. The first thing he did was swap the rear H&R sway for a GT3 rear sway which was set to one hole from full soft. This made a huge difference and the car became a lot more benign. You could charge a corner hard while braking and turning and the rear would still remain relatively planted (compared to before). There was still a bit of oversteer mid turn.

It wasn't until the front uprights were swapped to the GT3 cup units and the much stiffer front GT3 sway was installed that really made the whole package shine. This was by far the fastest set up (4 seconds faster than #3 on a 2.55mile course, 1:57 v. 2:01) and I had to relearn how to drive the car as the only way to rotate the car now was to do it under braking with the front tires loaded up (I hated it at first as I couldn't get the car to turn). This set up required that you had to raise you speed on turn entry (delay your start of braking) and carry higher speed through the turn all the way to the apex and which point power could be reapplied very smoothly. If you get on the power too soon, you will unload the front end and the car will plow straight ahead. The whole idea of "raising your minimum speed through the turn" is what makes the car faster and drops your times. Having a car that is stable under hard braking while entering a turn allows to to charge hard. I began to understand this once I got the hang of changing my driving style as all of the sudden I began to eat people alive on turn entry as I was carrying so much more speed now going in.

I have since swapped to 1100/1200 rates which made the car even more planted but is still a little bit on the soft side when charging hard. I am in the process of swapping to 1400/1500 which is incidentally what I was told to go with from the get go.

You mentioned a 997GT3RS. Yes, out of the box great handling cars on what are relatively soft spring rates. You really can't, however, compare the 997cars to the 996 cars as the suspension pickup points are quite different resulting in much lower roll centers on the 997GT cars compared to our cars. You have to use much higher rates on our cars to keep the roll in check especially when you take into account our greater weight. Incidentally, with good shocks, I have found 1100/1200 quite pleasant on the street when compression is set fairly soft, actually comparable to the H&R coil overs, just a hair stiffer but less harsh.

I have I learned one thing in all this, a loose car may be fun at drifting contests or if you like to have the back end step out but does not make for fast lap times... These cars really work well with a square spring set up. Hope this helps.

John...

 

Thanks for your input. I have definitely come to realize that the PSS10 spring rates are waaaaaay too low, but would be very hesitant to go as stiff as your setting. Especially considering my car is a dedicated street car. I'll keep my cheap to operate E46 M3 track car.

I can also understand that the front spring rate is causing a lot of the "wallowing" being that it's sooo soft. I'm really surprised that the PSS10's are set so soft and appear to be under-damped for the standard spring rate. I have mine set at 9 front and rear and the spring still feels as if it's over-powering the shock.

It does seem that it would be very hard to put the power down on the street with a 1,200+ pound rear spring rate. It might work fine with hot sticky tires on a road course, but how about the street?

Keep in mind that I'm not interested in the ultimate lap time, just a more planted and balanced street car. My car has a lot of front grip, but on a scale of 1-10 (10 being the best), I would rank planted as a 2 and balance as a 3. My M3 has 275/30R19 Michelin PSS's on 19x9.5" wheels at all four corners, stock swaybars and Ground Control street/track coil-overs and it feels 1,000 pounds lighter than the 911 at turn-in and mid corner balance.

OP, it would be very helpful if we knew what kind of springs/coil-overs you're running. Give the experience of pwdrhound, you may need to work on you spring rates first.

Later, Steve

 

I ran just the H&R rear sway with stock front for 6 years loved it. No snap oversteer. Setup is always a total picture and the H&R on full soft offers plenty of understeer (obviously pending the rest of your setup). In fact the stock front was diving too much on turn in because of the discrepancy and I found a great deal on a set of GT3 sways. I would have gladly just got a front adjustable sway.

That being said, I do like the GT3 front and rear sway better because it offers more control and more setup options as the LAST thing I like to do is play with adjustment ***** on coilovers.

 

Steve,
Everyone is scared of stiff springs. I know I was. Stiff springs absolutely suck if you have crappy shocks. In order to run stiff springs, you will need high quality dual adjustable (at a minimum) motorsport shocks like Moton, JRZ, MCS, Penske, or Ohlins. There is absolutely no issue with putting down power with my spring rates, even on street tires, quite the contrary. The stiffer rates definitely shine in tight S turns because the car stays nice and flat. Like I said, I find 1100/1200 with JRZ Pros better from a ride quality standpoint that my old H&Rs or RUF PSS9s. On the track it's no comparison. Having run a ton of spring and shock combinations on these cars, I would under no circumstances run anything softer than 600/800. I will have more feedback in about a week on my 1400/1500 set up. For a pure track set up, the rates for my car were actually calculated by my shop right at 1700/1800 but my current shocks will not handle those rates. To give you an idea, I ran a 30 minute session this past Friday in a track prepped 968 (about 2800lbs) which was running MCS triple adjustable shocks and 1600/1600 rates. Due to the higher roll centers on that car, the springs were actually a bit soft for that application as there was still a lot of roll present with the car loaded up in turns on slicks. Something closer to 2000 will probably be needed I was told. On Saturday, I ran a 12hr Enduro in a Spec Boxter which weighed 2600lbs ready to run with drives. Spec rules require PSS9s with a max spring rate of 450/500 if I recall. I spend over 5 hours in the car over two days during practice and the race, and the car felt very very soft even at such low weights. I got used to it after a while but you really had to be nice and gradual with brake application and steering input as anything more sudden really upset the soft chassis. Hope that helps...