Increase torsional rigidity on 996 cabrio?

Long time reader, first time poster... 2003 996 C4 Cabriolet with 89k mi, I purchased 14k/2 years ago. Love the car generally, but the flex bugs me a little. Yes, minor compared to other convertibles I've driven, and open-air driving is certainly worth the tradeoff (especially in the Bay Area, where I can put the top down 9 months out of the year). But still annoying. Thoughts on upgrades that might help? Sway bars, perhaps? And if so, what brand? I don't track it, FWIW. This is for street (preferably twisty mountain roads). (For the record, I did a few searches before posting, but didn't see any relevant discussion here.) Thanks in advance.

Do you really mean chassis flex or do you mean soft/worn suspension ? Similar but different cause/solution. At 90k miles, a careful inspection of the suspension components may be a good idea?

Roll cage does wonders for rigidity. :P

dude just drive the car..........and do not put a roll cage in the car..............unbelievable advise

My cab has a front strut bar in it but it came that way from a PO so I don't know what it drives like without it. I don't notice the chassis flex and I have a lot of really good mountain roads. I also have the M030 sway bars so that could be a factor in the feel of the car as well.

Thanks for the input so far. I think that the roll cage suggestion was tongue-in-cheek. A suspension inspection might be a good idea indeed. I'm probably getting the clutch renewed (and IMS upgrade installed), so it'll be going into the shop and I'll ask them to look. But they noted wear in (and replaced) the CV boots 4000 miles ago, and I suspect they'd have looked at the suspension while they were in there. Assuming that there's no suspension wear issue to resolve, though, any thoughts? A little research suggests that conventional wisdom discounts strut bars, but that could be my misinterpretation.

I don't know if a solution exists for 996 cabs. I know the feeling - chassis flex for C4 Corvettes is horrendous. The roof panel is structural and the car suffers when it is out; many of us use an empty targa frame or an aftermarket brace to stiffen the chassis. Some ragged-out Vettes get so sloppy that the targa panel can't be reinstalled unless the car is parked on flat ground. I don't think there are sufficient hard points for the 996 to do something comparable to the Corvette-style braces. I'm not sure the hardtop is supposed to be structural when it's installed, and I wouldn't expect the mount points to be robust enough to carry significant load. My 986 was fairly stiff for a Cabriolet, but it was nowhere as stiff as my C4 Coupe - not even close. It would flex (and even creak) pulling into driveway aprons, whereas my C4 coupe will pop a wheel off the ground going into almost any driveway. It is ridiculously rigid. I know there are strut braces/trusses for the 996, but I don't know of any aftermarket product designed to reduce/eliminate chassis flex/twisting.

I have noticed more flex than I like in my '02, I would say on a par with a Miata, and not half as stiff as an S2000. I doubt sway bars would help, I would think the flex has its roots in the fact that the Cab was not designed from the beginning as a drop top, and suffers a loss of ridgity from absence of the coupes top. I believe that some have had some success with adjusting the door catches, the floppy doors are the thing that really bugs me. I will address this in the future, but need to source some new catch screws, as the top one is stripped, more than likely from a previous attempt to adjust using a torx wrench rather than a double square.

The default suspension is pretty loose so there may be more there to gain than you think. I just from KW V3 coilovers and GT3 sway bars back to stock suspension. For daily driving, I love it. Grips good enough on the on ramps and I can go down roads at 60 that I had to slow down to 20 on. It almost feels like a 4x4 and since they graded my road to the soil and haven't gotten the asphalt back down its a good thing. But I did 3 sessions on a track a few weeks ago and was very frustrated. It wasn't near as fun with stock suspension. So yes, I think upgrading the shocks and the sway bars will give you a more rigid feel and definitely help it grip better. While you may still feel some twist in the chassis, the stiffer suspension should make up for it.

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It's not. Actually, when I have the hardtop on, I notice the flex even more, because it rubs against the windshield frame. Some silicone lubricant helps the sounds.

Bummer, although it's not really a surprise. If you've ever had a car (like a Corvette, or an old Camaro with t-tops) where the panel(s) are structural, you know what a pain in the butt it is to remove/replace 'em. Sounds to me like you are already resigned to the fact that the flex you're describing (the top shifting when cornering or when you load opposite corners) isn't going to be completely solved with suspension adjustments...but if you can learn to live with it, it's still an incredibly capable platform. Just a little twisty (and maybe squeaky as it ages)...

If the chasiss is too flexible for your liking, stiffer than stock suspension would be a bad idea. Can you describe the exact situation you notice the flex? Railroad crossing for example? I a thinking maybe just new shocks/struts after 90k miles? Not rock hard Konis ,just equivalent to OEM.

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Yeah. I'm really not even talking about top-up - I don't really expect that. I'm talking top down. But loading opposite corners is a good description. Could be, especially if what I'm hearing is the suspension. I'll see. Thanks, all. Apologies for my ignorance.

The cab has a reinforced chassis , the series two cab is even stiffer than the early chassis . My first check would be the suspension and all the bushes .

The 996 Cab is pretty stiff as Cabs go. They are very respectable compared to their Ferrari counter parts. I question the age of the suspension if that's not giving you a false sense of what you are feeling. The open top motoring is a trade off. The coupe is always the "no compromise' option that is hard to duplicate with any open top sports car.

Get the ROW M030 suspension. Gets rid of bounce and body roll without being too harsh. Not too expensive too.

No amount of new suspension parts - stock, RoW, or aftermarket - will address OP's original question of how to "increase torsional rigidity on a 996 cab..." As TheMystro pointed out, the coupe is going to be stiffer than the Cab - and a C4 coupe with the additional bracing for the FWD stuff is going to be the stiffest 996 you can get short of a GT3 or a car that's had a welded tubular cage installed. OP, perhaps this is a reason to buy a second 996, so you have a rock-solid coupe AND a cab...

get the row m030 it'll do you some good

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I was able to hang around the shop last time my mechanic did maintenance. I'm not sure about the hard top, but he indicated that it's good practice to have the top closed when putting the car on the lift as it does add rigidity to the chassis. I'm not sure where you're at, but you can catch a ride in mine sometime if you around the LA/Long Beach (CA) area. My cab only has 20K miles and mechanic tells me it's a really tight chassis. I wouldn't know, it's my first Porsche and first cab...feels pretty flexy and creaky to me haha. Maybe it'll give you and idea of what it should feel like and see if that's good enough.

There are always compromises. ;-)

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x2 The only things I can think of to reinforce the chassis but not guaranteeing if it will actually help in a Cab would be the Elephant Racing X bar for the front and Brey and Krausse Harness bar to tie in the upper seatbelt mounting points for increased lateral stiffness. If you go over the top with the top tier version, you maybe able to dial out some torsional flex as well. Obviously with any of these items, you will lose some usability in that space.

Interesting. I've already pulled the back seats, because they're effectively useless - and without them in place, a smallish dog can be comfortable under the windblocker.