I have had my 996 TT for 9 months now and have gotten used to the driving dynamics of the car. I am trying to get my car closer to neutral as I am not pleased with how much it understeers.
Having had a NA 993 in the past, I got big kicks out of the oversteer and the ability to steer the car with the throttle and really wish this car had more of that capability.
Having said this, I know the extreme would be to disconnect front drive shaft and get a GT2 rear diff. My fear is this may be an extreme too far the other direction with massive oversteer, then I put the thing in a ditch.

Aroud this, I have a few questions for the forum: (this is for mostly general street use along with spirited driving on twisties and very occasional track use (like MAYBE one DE per year).

Has anyone taken incremental approaches to get the understeer out while keeping it AWD?
Has anyone gotten their TT to a nuetral dynamic with perhaps a 'lean' toward oversteer with suspension tweaks and closing the gap on the front/ rear tire widths?

Here is where I am at present: I have put H&R Coilovers on the car and it feels much better, but still understeers. I have ordered the rear H&R Sway hoping this helps to a large extent.
If this doesnt get me there, then I will get the front sway to soften up the front to dial out even more understeer. The last thought would be to close the ratio of the front/rear tire widths. Like 235 or 245 on fronts while leaving 295's on rear.
For those that have increased front tire sizes for this reason; Did you just put these on TT stock wheel dimensions or go to a GT2 wheel width, and which is preferred? (from an aestethics persepctive, my preference would be a larger wheel width) but not sure if it matters all that much.
I understand it may never be possible to get the car to oversteer like a RWD car, but am looking for solutions that will at least allow me to step the rear out without putting the car at the very 'edge' to do it. Based on everything I have read on this in the forum, these appear to be the steps to take to get the car where desired, and am guessing its allot of trial and error with each iteration of changes to see if the car handles as desired with each change...but am just looking for feedback on what others have tried and experienced making these types of mods.
Thanks in advance for the feedback.

~Ken

 

I'll let others talk about the suspension changes, but one thing you must keep in mind with the AWD and tires is, there is a very narrow window for tire size and revolutions between front and rear before you will blow the front differential. I'm not sure you will be able to only change the fronts. Others with more experience can clarify this.

 

About tire sizes,you can only use two size combos...225/295 and 235/315...as you stay AWD...if you go RWD you can do whatever you like...
as for understeer it is what i hate about this car...Set front camber to maximum negative (it should get you at -1,5deg) and set front sway to full loose while rear sway to full stiff...also set front toe in to +1,0mm total...if you do them one by one you will observe differences better and find what is best for you...I ve tuned 996TT suspensions with GT2 ride height and pss,jic and kw coilovers but not with HR coilovers...However i tend to believe that allignment specs should be simular...

 

+1 to Skandalis' post.

I was able to tune out the understeer in my car by making the rear sway bar max stiff, and front +1 from full soft. PSS9 settings were 3 in rear, 4 in front.

You will probably still experience some understeer unless you can get enough negative camber to make the front tires stay flat on the ground during cornering. That is probably more like -2 to -2.4 degrees, but that is a track setup, and will probaly cause excessive wear on the street.

There have been several threads in the last two weeks discussing suspensions and alignment. You should take a look at those for some more details. A lot of good stuff in there.

Jon

 

Ken,

Give Steve a call. Not sure if you know, but he is first and foremost a racer (has driven Champ Car Atlantic Series, Koni Challenge, and will be driving World Challenge next year) and he'll be able to get you set up. I felt exactly the same way when I got my car. The suspension helped but removing the front drive really made a difference. I don't think you have to worry about putting the car in a ditch. It is a really quick job and inexpensive. I'm sure you could work something out with him as well if you weren't happy with how it drive RWD.

 

Hi gents
Couldn’t you get a bit more over/under steer by moving the weight distribution when you set the corner weight? Ex: move weight a bit more to the front or the back?

 

So why wouldnt 235's be an option with the 295's on AWD? More grip up front will tear something up??? I have heard of others putting the GT2 widths on TT's and didnt think it was an issue. I was just thinking/ hoping only altering the fronts would dial out some understeer.

 

AWD has the inherent problem of causing corner entry oversteer then switch to push.

You can try to tune it away a little but you can never cure it.

Tips to make things better to start:
As above mentioned, stiff sway rear and soft front. But this will also make entry oversteer worse.

To fix this you need to add some compression on the front shocks, and take away some rebound (softer) rear. Not too much as car starts feeling soft at higher speeds.

Next step go soft on rebound front (so you still have front grip when starting to accelerate).

But, if you don't have separate adjustment on compression and rebound you can't do it.

And these are all band-aid solutions to a 4WD configuration that will just never be balanced like a 2WD Porsche.

Whatever tire tricks you do, it will still have the same general behaviour. You can get the car to come around nicely with the rear as you enter a turn and you are feeling how that line was just perfect, and you're getting onto the gas to maintain your perfect slip angle on the car but... all of a sudden it starts to push. Unless you're "over on the other side" with a for 996 big slip angle, then you break into a drift (slow). 4WD problem, your window of balance just doesn't exist, as it changes around mid turn.

You seem to be a driver type of driver. Go 2WD. Add caster front by help of GT3 Cup camber arms for better camber compensation when you turn and you don't have to do massive changes with uprights etc unless you go really hardcore and have lots of $$$.

A word of experience and heads-up for your expectations: 996 will never have the same playful yet fast rear end feel as 993 ever had, in which you can drive like crazy and it's all rock'n'roll and the more power you put out rear the funner it gets still in 100% control, nice balance even with a few degrees "drift" and fwd momentum.

You are fast when in check with 996, or you are more or less "drifting" but losing all speed if you try to play, especially the grippier your car is. There is an incredibly tiny rear end slip angle window in 996. The basic 997 chassis took a noticeable step back towards 993-style playful characteristics with a bigger slip angle window to play around in as a driver.

 

It's not a grip issue. The problem is that if the overall tire diameters differ by more than a few mm, it will burn out the differential. I am not positive, but I think that what happens is that the car senses the difference in driveshaft speed caused by the difference in tire sizes, and assumes that the tires are slipping and so it overcompensates.

Jon

 

I've actually run 235s and 295s amd prefer the setup on MPSCs... I've had no issues with my diff (knock on wood)...

Mike

 

Thanks for the really clear explanation of something I have felt in my car, but could never articulate.

I've learned to drive the car so as to if not take advantage of, at least compensate for, this behavior. Turn in a bit early, let the oversteer help with rotation in the first half of the turn, and then unwinding to get on a larger radius on exit to compensate for the push. I try to envision the exit point about 3-5 feet inside the curbing and let the car push itself out to the true exit point.

 

This is exactly what I am doing now. If I take PSM off and its a little wet, the feeling is 'similar' but nothing like the 993. I actually even took a performance driving course, and the only way I was able to get *** to kick out on a wet skidpad was actually to let off the gas a little...then keep in and out of the throttle but it only tried to come around when off of it.
I will play with these few things to see what I can come up with my alignment seems to have taken some of it out along with the coilovers, so with sways maybe I will be able to live with it. If not, I may be going to RWD at some point.
When you go this route, I assume you have to change rear diff to GT2 spec, so not just one wheel spins...correct?
Also, does PSM still work when you do this, and does it help to bail you out much if its gets to squirelly??

~Ken

 

Yep +1 on that driving style! No more of that for me in about 1-2 months as I am going 2WD on this one.

Oh another note - the 4WD config is UNBEATABLE on rain and damp. Killed a full race GT3 Cup on rain with a bone stock Porsche dealer democar, a 997 C4S, not a bad driver either in the racecar (a competitor from the series I raced then), with 4WD I just had much better exit speed, every time. As it dried up, I had no chance anymore.

 

2WD yes get a Limited slip diff, whatever kind you prefer. Carbonetic makes a really good one that lasts a very long time and gives really good traction.

PSM still works but how perfect others have to chime in as I haven't tried it myself. Generally it will still notice when your yawrate kicks up dangerously and regulate brakes here and there to keep your from a spinout. Also if you get wheel spin the traction control part of PSM will also reduce engine torque.

 

+1

235 and 295 is ideal on Turbo wheels imo.