New to 997 TT, and experienced understeer.

In a curve, at 65 mph, not at full throttle, but at 30- 40 % throttle position, and experienced understeer.

Curve is not soft, it is a sharp curve.

The moment I backed off, front nose gained traction again.

Is this understeer because I wasnt full throttling, but just slighlty accelerating? Would the front tires grip harder if I would full throttle?

Trying to know the 4WD system.

 

First, go get a geo check! If you want less understeer you can:

- increase negative camber
- put on some aftermarket adjustable sways and soften the front sway and stiffen the rears (will give you more oversteer)
- put on some grippier tyres
- keep a constant speed through corners to maximize grip (10% throttle) and only accelerate out of the corners, not through them! A tyre only has a finite amont of grip, if you use some of that grip for accelerating or decelerating then you take away grip from cornering...

By the way, this has nothing to do with 4wd! In fact, with more weight over the front tyres in the 4wd cars I actually find you get LESS understeer in 997s. One of the reasons why I prefer 4wd road cars.

 

Well said. Alex

4WD should give you more confidence while entering and exiting the corner.

Only drawback on the 4WD to me is the weight it adds to the 997TT compared to GT3/RSs, just my 2cents.

I have replaced my suspension with damptronic. Night and day difference. a MUST for the list of mod.

Enjoy the car in good health!

Cheers,

 

Alex,
could you advise some of the aftermarket sway bar manufacturers?

 

I imported some GMG sways (as per my signature) - they have 3 stiffness settings. I use soft on the front (still stiffer than stock) and medium stiff on the rears. Works well. If I do more track stuff then I just switch to full stiff on the rears.

-stiffening the sways on one end makes the other end of the car have more grip!

I would definitely rule out a bad alignment though. I knocked my geo out when I was driving on some cobbled Swiss pass roads back in 08, I was understeering all over the place after that. Got back to the UK and fixed the geo and could corner at very high speeds again.

Stock geo settings should be (in red):



Note that all of us with modified suspension above are all running more negative front camber for more cornering grip. However, to do this you need to lower your car and to do this you need to upgrade your dampeners/springs as the stock suspension doesn't allow for adjustments...

 

Alex, "guru", I cant lower due to daily driving.

Would I benefit from getting aftermarket coil overs as well?

 

I am -15mm front and rear and I can drive straight over the various array of concrete speed humps we have here in the UK:



My ride quality is also no worse than a stock Turbo in sports PASM mode.

Coilovers wouldn't help you directly with understeer (unless the road surface you are cornering on is really rough).

As I say though, get down to an OPC or a geo alignment specialist and check you don't have anything wrong first. You have to be doing something pretty over-the-top to get a stock Turbo to understeer on public roads in the dry!

 

"Is this understeer because I wasnt full throttling, but just slighlty accelerating? Would the front tires grip harder if I would full throttle?"



Full throttle would not decrease, but would increase your understeer. Full throttle (if there is acceleration) transfers weight to the rear of the car and in turn decreases the weight on the front tires, therefore diminishing traction. The reverse is why the understeer stopped when you lifted out of the throttle, the weight transfered forward providing more grip on the front tires.

 

Lift off oversteer is not what you want though. You need to keep your speed constant for maximum grip through a corner, thus need a small amount of constant throttle to do so.

 

I had the same concerns, as well as concerns about the suspension being too stiff. Having said that, I wanted less body roll, less oversteer and a more controlled feeling midturn. I ended up with the TPC modified Damptronics, bars and links. Wasn't cheap, but the result is really impressive. The lowered ride height is fine, ride is a little stiffer but much more controlled, and much more confidence inspiring in the turns and much less body roll from turns/braking/accelleration.

 

Although there are exceptions to this statement such as an increasing or decreasing radius corner, it is generally true. If you are anywhere near the limits of adhesion in a corner, the throttle changes need to be very subtle so as not to induce excessive understeer or oversteer. You can feather the throttle or increase the throttle to maintain the balance of the car or steer the car with the throttle.

 

I think Alex summarized it perfectly...for most drivers, changing the alignment first makes a huge difference, followed by a stiffer rear anti roll bar.

 

Agreed with Alex et al, the key is max. out the negative front camber on your car, and if you have adjustable sway, make front softer than rear. These are the 2 fundamental changes.

But also don't forget to change to coilover with stiffer spring -- this is where the real transformation occurs.

 

kcturbo wrote

IMO this rule does not always play true on awd cars. Depends the the AWD system and its ability to transfer power ratios between front and rear diffs. My turbo and my Sti will understeer under partial throttle but when u mash in that situation the front tires actually start to help "pull" the front end out of the understeer condition. Of course for most people its hard to even consider trying that when they are sliding straight at the apex of a turn, haha

 

>>>>>>>
kcturbo wrote: Full throttle would not decrease, but would increase your understeer. Full throttle (if there is acceleration) transfers weight to the rear of the car and in turn decreases the weight on the front tires, therefore diminishing traction. The reverse is why the understeer stopped when you lifted out of the throttle, the weight transfered forward providing more grip on the front tires.
>>>>>>>

>>>>>>>
r6cairo wrote: IMO this rule does not always play true on awd cars. Depends the the AWD system and its ability to transfer power ratios between front and rear diffs. My turbo and my Sti will understeer under partial throttle but when u mash in that situation the front tires actually start to help "pull" the front end out of the understeer condition. Of course for most people its hard to even consider trying that when they are sliding straight at the apex of a turn, haha
>>>>>>>>>>>>>>>>>>

Handling dynamics talk -- cool!

In relation to the title of this thread, there is very good article here: http://www.autozine.org/technical_sc...handling_5.htm
The gist of the article is this: Yes 4WD car does tend to neutral steer (versus RWD's oversteer tendency), and there is an actual explanation. The reason has to do with the fact that slip angle increases when there is tractive force on the wheel. Tractive force on front wheel = increased slip angle front wheel = understeer.

For current discussion, I agree with both kcturbo and r6cairo, but... it depends on where you are on the curve that each point applies.
If you are in middle of curve with high steering angle, full throttle is a bad idea because of front/rear weight transfer causing understeer as kcturbo wrote.
Once exiting curve with car almost straight, the front traction of the 4WD provides the greatest advantage of being 4WD: traction and acceleration coming out of curve. So us 4WD Turbo owners keep this in mind, this point of exiting curve, =when car is nearly straight, is where we are supposed to go for the "kill." Turbo power plus 4wd traction = advantage Turbo.

All IMHO of course.