Squirrelly rear end in rain - new tires, new wheel bearing
 

Ok guys, I'm a little lost at what to do at this point, I was driving on the interstate yesterday and hit some rain, and suddenly my rear end gets a little loose, never lost control or anything but I could feel the rear end kinda moving on me a little in the rain, I just had a new wheel bearing put on the passenger side, and I have two new Sumatuma HRTZ II's on the rear end with less than 1,000 miles on them. I have posted about this problem before,

http://986forum.com/forums/showthread.php?t=15442&highlight=tires+wheel+beari ng

Do you think I need to have the rear wheels aligned? The car feels perfectly fine when its dry, The streets are pretty bad here in New Orleans so its reasonable that I could need a new alignment, but I just got the car back from the shop about 3 weeks ago!!!!!!!!

Alignment is recommended when installing new rubber. Are the tires the same front and rear?

What size front and rear tires do you have ? Incorrect size stagger can cause odd behaviors. What brand are the front tires? I would look at rear toe. Good luck!

Michelins on the front, couldn't afford to match the tires because I knew I was going to take a hit on regular maintenance and a few repairs over the last 2 months now pushing $4,500 all together....

I was thinking that it was an alignment problem on the rear end also.....

Sounds like a pretty big tire mismatch. Just don't lift your right foot unless you are going in a straight line.

Likewise, big tire mismatch. I'm not big on mixing brands or even styles of the same brand.
It won't show in the dry unless you're really at the edge, but in the rain, every little imbalance is magnifyed a hundred times......

I recognize the difference in the tires but there is no way that should cause my rear end to get loose in the rain going 55mph in a straight line.

I'm leaning toward the alignment being off.....

Wrong on the first account.

Correct on the last account.

The combo of both is never good.

A good way to tell if its your alignment's fault, in dry weather when you go over a bump in the road, with 1 or the other rear wheel, do you get a shimmy from the rear end of your car til both rear wheels have even weight loads on them/are flat on the ground again?

If so then your Toe isnt up to spec anymore, you'll need an alignment

CJ,

Don't want to hijack this thread and I don't go around smoking my tires all the time but, is a symptom of poor alignment also wheel hop on heavy acceleration?

In less than ideal conditions, if I make any effort to smoke the tires, the back hops all over the place. It also does this a bit powering out of a turn to (my sign that pushed it to the it to the edge).

Regards, PK

Nah, wheel hop is usually a worn strut and spring problem but balance and alignment could play a small roll in this.

IMHO of course, if you have checked the tire pressures and they are normal then the next logical step is to have the alignment reset to spec and the suspension parts checked for wear (the bushings). I would use a good Porsche Indy for this work -- the dealer will just say its the non-N rated tires.

We have Sumitomo HTR ZII on 02S and ran through a 2" downpour with no problem at 60MPH. IMHO, I would say its not the tires.

Take care, :cheers:
Ed

A 2" downpour in Phoenix??? :eek:
Is that 2" of sweat? :D

Annual rainfall in Phoenix is about 8". What they don't tell you is that most of it comes in 4 days. :)

There is nothing wrong with Sumitomo tires, they just have very different grip characteristics than PS2's, hence the mismatch. Match the tires all around, get an alignment and have an experienced Porsche tech poke around your suspension to make sure everything is sound. Do this before the next rainstorm so you don't become graffiti on some offramp. :eek: A little preventative maintenance is usually a lot less expensive than a hospital stay.

There's something that no one is talking about...

The Boxster has wide tires in the rear. Wide tires and wet roads simply don't go together. The same wide tires that give us great cornering traction in the dry penalize us by hydroplaning much quicker than a skinnier tire would in the wet. Boxsters just aren't very good in the rain.

Jack, we did several runs last year at the Dragon in the rain. The Boxster was simply amazing on the wet roads.

It's also part of the reason why my Boxster spun out...I've hydoplanned several times in heavy rain.........

We drive sports cars.....use at least least high performance tires,most of us run extreme or max performance summer tires....it's not going to be as fun to drive in the rain as a corolla,camry or bug.

I've driven mine in the mountains on wet roads as well. It was fun, and performed well. However, the OP in this thread wasn't driving on a wet road, he got caught in rain. That carries the probability of standing water at highway speeds, something I doubt your Dragon runs encompassed.

Hydroplaning doesn't happen when the road is merely wet, it happens when there is some water depth... something for the tire to get on top of. No reasonable person can argue that a wide tire is as good or better than a skinny tire at resisting hydroplaning. A Boxster is a relatively lightweight car with some pretty wide high-performance summer (dry weather) tires on the rear. A perfect example of a hydroplane waiting to happen.

At 70mph on the expressway in a downpour of rain, you're at a decided disadvantage compared to the Camry that just whizzed by you, like it or not.

Blink, I think your biggest culprit was the fact you did not have PSM.

wheel hop: shocks/springs

the rear end: i would say tire pressure and the mismatch.

if it was dry, then i'd say its alignment. toe it in some, then when you get matching tires up front, and figure out the tire pressures, then you can bring the toe back out to the orig spec.