Unstable on wet roads

I had my car recently alligned to factory specs, new PS1 tires. On dry the car is glued on the tarmac as it should be. When the road is wet, it starts to somehow "wobble" a little, as if it was porrly alligned! Does your do that too? What could be the reason fro that?

Does it wobble on dry? Does this happen only when you are braking or just cruising? The PS1 isn't really a good wet tire as it is dry. You sacrifice proportionaly wet or dry handling when you err to the other side.

LVDell: Dry grip is fantastic. It is happening when I am cruising on the highway at regular speeds (90-140 km/h). The PS1 only have something like 3-4000 kms on them.

Have you had them re-balanced? Do you have spacers?

No spacers. Wheels are balanced.

Sounds like the Cayenne wobble at cruising speed. Many have suggested that it can be as serious as having to replace the driveshaft and as minor as just getting the wheels rebalanced. One other thing, you could have very well got a bad set of rubber. But my guess is on the balance issue. Aside from that, I am out of diagnoses.

One other thing. Do you have another set of wheels/tires for the car? Like a track set or winter set, etc.? If so, run them and see if the vibration is still there. I am beginning to think you have a bad set of tires. They could be not true (round) or have a flat spot which would lead to this.

Please describe the "wobble". A 911 will be less stable on any road when there is standing water. If there is a lot of standing water and speed is high enough it will aquaplane very easily. Rgds,

This sounds like hydroplaning as the problem does not exist on dry pavement and you describe your car as essentially stock.

It certainly feels like some sort of hydroplanning as the wheels seems to be "sucked" in the wetter spots and the car becomes much more sensitive to laminated tracks on the road. I'd be OK with that phenomenon at higher speeds, but am reluctant for that on a 996 at around 130 Km/h.... Isn't that a rather low speed to get those behaviours?

As dumb as this sounds, I would be inclined to go to another dealer and recheck the allignment. Before that, I would pull every tire off the car, put it in a balancer and make sure it is round and make sure you don't have a bent rim. Also, look to be sure that the weights are distributed evenly around the circumference and you don't have excessive weights applied for balancing. 2 smaller weights 60degrees apart is better than one large weight centered. Then, I would retorque them (I mean personally) so that no jerk did it with an impact wrench. I'm sure you have already checked pressures carefully. I have been around long enough to see many mistakes due to lazy or inexperienced workers. I once took my then-new SC from the dealership after new rears, and found the instability to be due to 90psi in one rear tire. One new set of tires had a tire that required a huge abount of weight in one area which caused it to feel out-of-round. Ones set of Pirellis suffered belt shift. If everything checks out, i suspect the most likely answer will be one bad tire. Let us know. AS

I have had bent rims on my 993. It does not feel like this. The wheels are balanced by a proper mechanic. Pressures I have checked and gone back to OEM Porsche settings, just to make sure. Could be wrong torquing of the nuts, and somehow it shows more on wet roads. Good hint. Will check it out and get back. Or let me put it this way. I know 911's favorite surface is not wet roads. At what speeds on wet do you guys start to feel rather "uncomfortable"?

Maybe others can chime in on the wet road condition, but I don't drive on wet roads. We rarely get rain here in Las Vegas and when we do we know in advance so I stay away. Last time I tried to drive in the rain here I lost control of the car at <20mph!!!

This may be s stupid question, but you mentioned "new" tires. The first 50-100 miles are notoriously slippery because tires come out of the mold with a residue which takes some time to come off. Wet road surfaces will definitely exacerbate the problem....

Sounds just like the symptoms of worn back tires. You do not mention whether it is loose in the front or the back. As a properly aligned 996 has a negative camber in the back, the inside of the tires will wear down to the belt while the outside half still looks good. You do not notice any handling problems on dry roads, but as soon as you hit wet ones, the back end will feel like you are on ice. But since you say you have new tires, I would check the camber setting.

Tires have only around 3-4000 kms. thread depth looks OK to me. Sounds like I need to go back to a store and get allignment checked again. Thanks for hints. Will post results later.

Hydroplaning. 130 k/ph with ANY standing water is a likely scenario. The car is traveling on some pretty wide rubber. These cars only handle like magic when on dry pavement and semi magical when wet. If I get caught out in the rain; I age 50yrs and go SLOW, I don't want to wad my car up. They are fun to hang the rearend out when it's damp.

If you are running good quality tires, rain does not effect the handling of these cars much at reasonable speeds. Standing water is another story.

It probably hs excessive rear toe in. That makes the rear steer itself a little depending on which rear tire has the most traction.

let me guess......In your Opinoin......tires never were out?..... DO tell , how rain does not effect how a car handles?.... standing water?.....When did you get the stupid idiot award?...and when did you master it?...

OK. Back from allignment shop. My values were way out of whack...!!!!! So much toe-in on my back axle must have created this handling behaviour. How did they change so much is a mystery. have not tried on wet yet. Am eager to see how the car handles on wet; on dry it turns in faster. One thing though, wheels produce less road noise. Does anyone run toe out on rear and toe in on fronts?

I had to drive my 996 an entire day through all levels of rain on Friday. It handled better than I expected. No wobble.

While the suspension changes may have fixed your problem, don't discount the possibility of hydroplaning also being a factor. The absence of the problem in the dry suggests your situation may have been a product of the two. While a number of factors influence hydroplaning, including tread depth and pattern, depth of water, tire contact patch and vehicle speed, the easiest variable to control is speed. Hydroplaning occurs because the tire is moving so fast that the tread cannot displace the water and the tire loses contact with the pavement. 130 Km/Hr could be easily 50Km/Hr too fast, depending on conditions.