eDoug

My first post here on RennList - I've spent lots of time lurking and searching, posting a bit on RennTech from a blown engine
(okay - let's not go there on my first post! ).

I have a 2002 C2 with 33k miles (pic below), I have about 3k miles since purchase, and still breaking-in the new engine, only 1k miles more to go. I replaced the tires after purchase with Michelin Pilot Sport Ribs (N1-spec), 225/40/18 F, 285/30/18 R. So, 3,000 reasonably spirited miles on mountain roads and probably 60-70% tread remaining on rears.

I'm seeking feedback and comments on two items. I've searched the forums and there are hints at these topics, but nothing concise in my opinion.

1) Over 70mph in rain, on the interstate, with a bit of standing water, but not deep the car feels completely unstable. This undoubtedly is hydroplaning - and the rear end has even skipped out ever so slightly when changing lanes. Seems fine at 60mph. I found the calculation someone posted about 9x SQRT(Tire PSI) being a MPH threshold for hydroplaning when water depth > tread. This too makes complete sense. This is my first p-car, but I've driven lot's of high performance cars and never skimp on tires - I've never experienced so much instability at speed. Of course, this is probably weight related and weight distribution related - but do others share this same phenomenon? I understand the "fix" is simply to slow down - but I can't help but be curious about it - looking for confirmation that this is not uncommon.

2) I've taken the car out into an open parking lot, very wet, some standing water - very few light poles. We have a local car dealership that just went out of business (their loss is my gain). I thought this would be a good venue to try to find some of the balance / threshold characteristics of handing. For lord's sake - it's almost impossible for me to break the car loose. I've turned off PSM and tried to get the back end loose if I lift of the accelerator (I understand PSM kicks in with heavy braking). The only behavior I can instigate is severe understeer when heavy of the gas - I've been unable to get the back end to come around. Heck - I'm just trying to get myself familiar with the car - and it hasn't ceased to amaze and puzzle me. I'm scheduled for a DE in a month and look forward to learning more in the seat with an instructor, on the track... What can I say - I'm puzzled only because I've read so many stories of folks losing it in the rain - is this just the wide rear tires that are at work here, are Pilot Sport Ribs miraculous tires, or am I just not going fast enough (probably 30mph or so in a confined space)??? In a BMW with traction control disabled, it's pretty easy to break the rear end loose with hard braking in the wet - also, PSM doesn't seem to limit power-induced understeer, is that right???

Hope this is a worthwhile post - thanks in advance for some of your thoughts. This is a great forum - and I look forward to learning enough to contribute constructively in the future.

2002 C2, Black / Black / 6Sp / PSM / Turbo Look 18" / Adv Tech & Design pkg

Malakas

Very nice looking car, and congrats on the new motor.

I've experienced unstable driving in the rain at freeway speeds twice: 1. when a rear rim had a bend in it (rim fixed / replaced and it drove like a champ in the rain), and 2. when my tire pressures were unevenly low (once pumped back up to spec it was fine).

It terms of breaking the end loose... I'd rec starting with an autocross to learn the traction limits before a DE. The first month or two with the car, I tried some "spirited driving" and the **** would not budge (running 295s at the rear). Then one day I was going a long at about 40mph and turned in slowly for a 90 degree turn, just before the apex I went WOT.... that was the first time PSM saved me money.

Good luck - have fun - safe motoring

eDoug

Thanks Malakas - Porsche CPO warranty covered the motor (Failed Intermediate Shaft) - I'm lucky, I know.

Regarding wet handling - Handling is just great below 65mph, only seems to get "jiggy" when I'm at 75 - 90mph. I don't dare go any faster in heavy rain. So, you can drive with good stability at 80+mph in a heavy rainfall?

Checked tread, checked tire pressure (running std 36/44psi), had an alignment done less than 3k miles ago and should have been done with engine was swapped - but that's what I'll check next.

Having strut bearings replaced with tech inspection for DE... will check in in a week or two.

Cheers.

Jim 'n' SC

YOUR DRIVING IN THE RAIN?

eDoug

I purchased this car with one thing in mind - to drive it as much as I can. I'm a home-office worker and driving/riding is what I do for fun... It's this, and my Beemer R1200GS "Adventure" bike. When it rains - the bike's not so much fun.

Living in a place with nearly no traffic issues, and miles of mountain switchbacks and the Blue Ridge Pkwy around the corner - I put 20k miles on the bike last year, going just about nowhere, from NC to Florida, to New Hampshire, etc... On the car, I've logged 3k miles in probably less than 8 weeks of driving time (in the shop for 2 weeks).

My only question is, why be scared of the rain??? Driving in the rain is so much more fun! Of course, hydroplaning, not so much fun - I just want someone else to chime in that their car hydroplanes as easily as mine in heavy rain at 80mph!

Okay, I'm done... need to go out for a spirited drive now. Hope you are too!

Macster

Cars with modern high performance tires, wide ones at that, are a bit skittish in rain.

At speeds I could get away with in another car with narrower tires, or tires with a more agressive (all weather) tread pattern without fear I find to be too fast in my Boxster, even when fitted with new tires.

Pirelli tires to me deliver slightly better wet grip than Michelin tires but neither is a real rain tire...

Be aware too that even in a light rain most roadways will collect water where the tires of vehicles travel and one can suddenly find himself driving in an inch or more of water for some distance, especially if road not traveled by another vehicle in a while which allows water to build up.

Another problem is water over the roadway for poor drainage (or even localized flooding). After water drains away water can leave layer of fine mud that is slicker than grease.

In areas of country where rain infrequent for long periods of time first rain even if not heavy and in fact especially if not heavy will render roadway slick.

Crossing 58 highway outside -- heading east -- from Mojave some months back and encountered heavy rain. Tires of vehicles ahead made what looked very much like soap bubbles. This from water mixed with dust, oil, etc. on road.

After a good heavy rain that washes this away grip in wet can improve, but still of course no where as good as grip when roads dry.

If tires worn or improperly inflated situation even worse.

Best advice I can offer is to in wet slow down.

More than once I've been passed driving in marginal traction conditions (rain, snow) by a vehicle only a few miles later to come upon vehicle on side of road after losing it in the wet or snow.

In one instance on I-70 east of 65 highway in a light snow storm drove 10 miles or so to next exit and took exit to try out car in snow (snow depth about an inch on secondary road. After just a few miles had enough and turned around and drove back to freeway. Got back on freeway and headed west back to 65 highway exit. On way back west spotted 6 or 7 vehicle off road in the space of under 10 miles. No snow build up on freeway but enough blowing snow to cause it to be slick.

Funny, sort of, but even as people standing on side of of road next to crashed vehicle, some with tow truck already there, or in one or two cases with sheriff or highway patrol car present, other vehicles just blowing by.

Made my way gingerly to exit and then south (still being careful) to my parent's house 20 miles south of there.

Sincerely,

Macster.

cdodkin

Toyo T1 is what you need - best wet tire I've used to date - awesome.

Tested my first set in the UK - and it rains there quite a bit!!!

Leigh2

eDoug,
Welcome to the forum.
I've had three 996 Carreras (+ 2 X GT3)and have experienced the instability that you mention. Certainly the tires are very important as you have recognized and the Michelin Pilot Sport series are spectacular tires. The stock springs however do give the car a very "floaty" feeling and I'd highly recommend changing to sport springs. I used H&R springs which did little to the ride comfort but made a HUGE difference to the handling and stability of the car accompanied by changes to the alignment. A search of the forum will give you days of reading on both of these topics so worth digging into.
Your experience in the parking lot is a good introduction to the world of 911 driving where it's pretty tough to get the rear end to break loose when accelerating; nothing exits a corner like a 911. The tricky part happens when you are braking and turning at the same time which is why the PSM kicks in while braking even when the switch is turned off.
You'll learn a ton at the DE day; have fun!

RF5BPilot

Wider tires are more likely to hydroplane than narrower ones because it is easier to flood the tread. I agree with Macster that sometimes it's not just deep water, mud and silt can make an area that drains across the highway more exciting than you really want.

Note that the general idea of twice the tire pressure, minus about 10% is the speed at which your tires completely lift off the road (assuming the tread is actually flooded; the water is deeper than the tread). So, approaching that speed--you have less and less contact patch on the road. It's gradual. If you combine reduced contact patch with uneven or worn road surface that pushes the tires laterally, you can have a jump to the side that is more than simple hydroplaning.

Yet......the insidious part of hydroplaning is that the front tires are the first to go because they are in the deepest water. While completely lifted off the road, floating on water, they can push enough water to the side so the rears still have contact. Old DOT films on test tracks show cars driving along with the front tires completely stopped--but they contine down the road because the rears have traction. Eventually, they lose control because the fronts have no traction--but at that point, they are still at full speed, making the wipe out unrecoverable.

This would suggest that if the rear of the car feels unstable--it may not be simply due to hydroplaning (because the rear tires should have better traction than the fronts). Not sure who did your alignment, but you might want to revisit that. Changing your springs will have no effect on hydroplaning. Your choice of a stiffer suspension is a personal one. All it may do is increase your tire wear and make the car less pleasant to drive.

Consider treating deep water like sliding on ice. Keep the front tires pointed in the direction you need to go so that when they get full traction again, they won't jerk you to one side or the other.

ElTorrente

You park your car just because it's wet outside? Why?

I drive my car no matter what the conditions - like it was meant to be.


I have the same tires as the original poster, and my car feels stable in the rain at 85mph+. I suppose the deeper the standing water, the more unstable it would be, but for the most part, in typical rainy conditions, it feels very stable. I think it feels safer than most people feel in their cars, given how slow most people go when it starts to rain - I feel like a speed-demon sometimes when I'm going 75+ in the wet and they are in the slow lane doing 50 on the highway.

perryinva

I'm curious as to whether 60-70% tread left after only 3k miles is normal for the Sport Ribs? I hate the crappy tires the PO put on my car (Sumi HRZ IIs), but the damn things refuse to wear. I don't mind replacing tires once they're worn a bit, but these still have 7-8/32's after 8k miles. I was looking to go with the Sport Ribs, but if they wear THAT fast, I might reconsider. I like to get at least 16k out of a tire...not too much to ask, I think, even for a sticky tire.

eDoug

I have a local indie mechanic who changes the oil, tires, non-warranty items. We were walking around the car on the lift and he mentioned that I was going through the tires pretty quick. He estimated I might get 8k out of the PS Ribs on the rear. Tire wear, to me, is a badge of honor - it means I'm driving the car and having some fun. I'm not drag racing from stoplights - but I drive almost exclusively on the twisty backroads and I push the car reasonably hard in the turns. I'm not racing to the corners to brake, but I put quite a bit of lateral load on the tires, and I'm driving on secondary roads and the Blue Ridge Pkwy (BRP) - I've heard the BRP eats tires due to the surface, too. I'd bet that if I get 8k out of the rears, a gentle driver could eek out 20k without using much throttle - but I'm no expert.

Here's a 3 mile stretch of road behind my house - a few switchbacks, and about 700ft of elevation changes.... it's brilliant. You don't need to drive like a maniac to just have fun in this car... Oh, and no potholes - we rarely get hard freezes, nor much snow.

Irksome

As to your second point, I also encourage you to get the car out to an autocross, or better yet, see if your local PCA has a performance driving school. San Diego region puts on a performance driving school twice per year, and it was phenomenally useful in learning the limits of the car and how to control it in panic situations. Autocross is good, but a performance driving school is better.

There is one huge downside to doing a pds or autocross, though... You may get hooked! If you think you're doing some spirited driving now, wait til you see what you do in those conditions. I took the pds expecting to never autocross again. I have missed only 2 events since then.

eDoug

Enrolled the 1st weekend in October for a PCA DE. Ordered my numbers today! Really looking forward to it. I've done two //M schools with BMWCCA at the BMW factory track in Greenville, SC and love 'em. This time, I get to use my own car, one that performs, hmm, like a Porsche! Very excited - thanks for the advice. Of course, in the BMW school, you're driving their cars and can be downright abusive... and don't get me wrong, I really think BMW makes an exceptional car (and motorcycles, too).