How to Correct Cabriolet Understeer

I am going on my forth year of ownership of my '99 Cab and would like to make the handling more neutral without spending a lot of money or making the ride harsh and overly stiff. I have spent 8 years of my life roadracing motorcycles and truly love motorsports racing but will purposely never track my car because I wouldn't be able to just do it occasionally. I don't need another hobby and all related stress at this time. Anyway, my car handles well but I don't care for the way it pushes the front in a turn when cornering agressively. I'm running 18" wheels with P-Zeros and have tried recommended pressures and less. The suspension is totally stock with a recent factory spec alignment. The handling is very noticeably worse with a passenger and steering is much slower to respond. I feel my driving technique is pretty good and smooth but often I will carry a lot of speed thru a slow turn (50-70mph) and the car will not respond but will continue toward the outside of the turn. I believe this is understeer, we call it pushing in motorcycle speek. If I slightly lift the throttle the car will hook up and I can make the turn as planned but at a slower speed. I'm wondering what components or adjustments I need to make the handling more responsive and diminish the understeer? Again, I don't want a race car ride, but I think I'm finding the handling limits to soon for occasional fun on the street. I have pretty extensive mechanical ability and can do most mods myself. Thanks for any help in this regard.

Alignment, tires, tire pressure all have an impact on handling....I would say you need suspension mods, X74, PSS9, or RoW M030....PSS9 will be the best ride out of all of them, but its not cheap...around 2k for te kit alone, not including install or alignment....you might also want larger sway bars. I have almost no undesteer in my C4 cab...but I have 19's and PSS9's....

Nick, I am afraid you do not provide sufficient information. What kind of Cab? What actual size wheels and tyres are you using? How much tread depth have the front and rear tyres got left? Is the tread wear even front and back? Not hard to measure either. There also comes a point of pushing too hard when you reach the limits of the grip on the front wheels anyway. For most normal road users understeer can be reduced by increasing the amount of grip on the front wheels and reducing the amount of grip on the rear wheels (increasing oversteer) by changing the tyres and their width relationship. The old 964 C4 responded very nicely to using 225s on the front instead of the standard 205s and without changing the rear tyres from the standard 255 width. My Coupe C4 is running the M030 option on 18 inch wheels so unfortunately I cannot provide specific information on the US version 996 Cab of either model, but I can tell you that once the front tyres get down to tread depths of 2mm and less you can have some problems with the onset of understeer when you don't want it especially if you live in a climate that is getting cooler at the moment. Also keep in mind the old saying; "start cheap and work towards expensive". Ciao, Adrian.

Adrian, My car is a '99 996 C2 with 7.5" front and 10" rear Turbo Twist 18" wheels, Tires are Pirelli P-Zeros, 225/40 and 265/35 and are about 80% and 70% good respectively. I might want to clarify the fact that the car behaves very well for the most part and by driving it smoothly I can approach a turn at a speed that seems way too fast, quickly late brake for an instant and initiate a steering change while getting off the brake and easing on the throttle seemlessly. For most turns this works very well and I can keep pushing the limits to the point where I have to quickly tell myself not to brake at all and enter the turn with the throttle to modulate grip. Of course this only works where my entry speed doesn't exceed physical laws. The car will most often push the front when entering a slow turn under full throttle in 1st, 2nd and maybe 3rd gear. If I let off the gas, traction returns, but my speed decreases quickly I think mainly from being scrubbed off in the turn. I'm wondering if at the slower speeds, weight transfer is an issue making the front end light and wanting to float or skim across the surface causing the understeer? It seems like that could be the case because tight turns entered at speed under light or neutral throttle don't seem to have the same effect and the front sticks better. Maybe some guys that track their cars can give me some input. Thanks, Nick

Firstly Nick you have to remember that a Cab has a tad more flex in it compared to a Coupe. I don't know the figures for the Porsche offhand, but the Aston Martin is rated with 28,000Nm torsional strength for the Coupe and 15,500Nm for the Cab. I would advise initially based on your requirements for ride comfort and cost restraints to play with the tyres next time you change them. How old are the current set? I certainly recommend you have the corner balancing checked to ensure you have the correct weight distribution over each wheel and that the weights are within tolerance if you are felling that the weight is moving around too much. Try adding some weight up front and trying a few experiments. This is the fun bit. Maybe you should consider a strut brace to stiffen the front up a bit. Do you have the ABD (rear wheel traction control) option? Somehow though after reading you are entering slow corners at full throttle that you may be asking too much it's a fairly standard setup Cab after all. Maybe you should try and borrow or go out with somebody with a similarily set up Coupe and see what that does under the similar circumstances. I have always found Cabs to be more wobbly than Coupes in the handling department under the same set of circumstances. Standard ride height (especially the higher American versions) Porsche of all models do tend to have a little float at high speed every now and again. Maybe you need to consider lowering, but that will increase your costs. Ciao, Adrian.

If you add H&R sway bars front and rear you can get the car to neutral or even oversteer if you go to full stiff on the rear bar. H&R sways use the stock drop links and I wouldn't change mine at all. It really helps with body roll too. I installed my sway bars when I had JIC coilovers installed so YRMV. Good Luck

For an oem solution, get the ROW 030 european sport suspension. Total with installation is around $1,100 - 1,200, and the change in the new handling characteristics of the car is unbelievable!!

Agree with Cydog! I have a 00 C4 CAB that I bought in the USA and then I moved to Germany and realized that with the stock suspension the car did not handle at Autobahn speeds and corners like it should. Changed out to the ROW M0030 and solved all my problems, can now drive at 150 mph+ and the car has no handling issues.

Nick, Based on the requirements, I would recommend to just get a set of adjustable sway bars (GT3 with TRG links) or TRG. Going to a more aggressive alignment will help add grip, but isn't going to effect the balance as much. I am not sure if you will like the ROW M030 ride because there is some harshness, especially on light bumps. Since you don't seem to an an issue with the ride or ride height, just a set of sway bars should do the trick. I would recommend to start with the front bar soft and the rear bar medium. Stiffening the rear will shift the shift the balance more neutral. Keeping the front soft will help with turn-in.

You'll want to carry less speed into turns and then accelerate out. When turning sharp corners, only brake 20-30% when you are turning the wheel. Most of time, you try to brake hard and carry as much speed as possible into a turn. You end up not able to turn your wheel when braking 70-80%. This is what I learned at autocross. As for mods, suggestions on suspension will improve traction at the expense of ride quality. I love how supple the stock ride is. However, I don't like the nose dive and wish the car is flat under braking. It's a trade off unless you get adjustable coil overs that has a wide range of settings which I haven't found.