996dancing at high speed!

Subject says it briefly, but i'll explain.. I have just installed two new back (same stock size bridgestone S-02) tyres and i kept the front ones since they're still in a good condition.. Today was my first run at high speed and getting over 200km/h the car sways left and right if i try to maneouver between other cars or change lanes. IT gets more evident over 240km/hr. The feeling is like wind blowing it on the sides.. I stopped for a pressure check and found out all the tyres were under inflated (30 to 25psi). So I added pressure for all the tyres to reach to 40psi (ambient temperature was around 31degC and the tyres were very hot, barely can touch them). The result is that the sway reduced or was it my mind wanting to accept that it really had reduced?? For the record, I also changed my clutch recently but i dont think that has to do with such a behaviour.. I monitored the coupling of the axle nut and they are surely tight. Could new tyres make such a behaviour? Any suggestions? Thanks, Wael 996 C2 199 6speed

That's typical of new tires (especially Bridgestones). You'll notice that they'll improve drastically with some use (250-500 miles).

Grant, thanks for the info.. Now i can sleep! I hope to get more replies that explain such a tyre behaviour.. wael 996c299

It was recommended to me that rears be inflated to 44psi and fronts to 39 psi. Any body else have any thoughts?

the recommended is 36/36 in the front hood of the car.. But at what temperature should this be? Dry season is starting here and i will have no less than 28deg in the night and up to 35deg in the day.. wael

Recommended pressures are usually at cold. I suppose that means after several hours of just standing, preferably overnight. I don't think it refers to ambient temp . 36/36 is recommended? I thought all 996's were 36/44?

That's also exactly how a loose rim feels. You might want to re-torque the rears (if those were the only ones disturbed). I wouldn't assume the competence of the tire changer. AS

Can it be that the tyres you bought are from two different places having two different storing tempratures and two different manufacturing ages? resulting in two different wheel performances? Did you check the expiry date of the tyres? Next time use Pirelli tyres!! I hope you are not fadz - C4S/02 <img src="graemlins/icon501.gif" border="0" alt="[icon501]" />

[quote]Originally posted by Fadi: <strong> Next time use Pirelli tyres!! </strong><hr></blockquote> Actually, I've had nothing but trouble from Pirelli tyres. S.

36/36 is for 17" 38/44 is for 18" Best time to set tire presure is in late morning when possible.

Hey Fixed Wing, That looks like my right rear S-02 about 3 weeks ago. I developed a slow leak and "poof", tread separation. Getting back to the original question, check the wheel nuts for proper torque, put a few miles on the new tires to scrub them in and give it a try. I've always been advised not to expect much from new tires (don't drive too hot) until they've been broken in.

[quote]Originally posted by powerfeed: <strong>Hey Fixed Wing, That looks like my right rear S-02 about 3 weeks ago. I developed a slow leak and "poof", tread separation. Getting back to the original question, check the wheel nuts for proper torque, put a few miles on the new tires to scrub them in and give it a try. I've always been advised not to expect much from new tires (don't drive too hot) until they've been broken in.</strong><hr></blockquote> All good advice. This tyre wasn't underinflated. No leaks found. Mostly the problems I have with the Pirelli relate to noise and vibrations. But good dry weather traction. S.

OK, tonight i have learnt: - in my case, 17in rims go for 36/36 at cold - I have to run the tyres for about 1,000km before going to Warp-9 - Pirellis, to my good guess, are worse than S02's - I'll check tightness of nuts - Never underinflate a tyre otherwise it will go 'poof'! Wael 996C299

[quote]Originally posted by Waz996: <strong>OK, tonight i have learnt: - in my case, 17in rims go for 36/36 at cold - I have to run the tyres for about 1,000km before going to Warp-9 - Pirellis, to my good guess, are worse than S02's - I'll check tightness of nuts - Never underinflate a tyre otherwise it will go 'poof'! </strong><hr></blockquote> It will go poof! in a very big way. Because of the hard sidewalls you will not get any warning of it being underinflated until the tyre overheats and the treads seperate. Most tyres fail because they get a nail or something in them and slowly deflate until the overheat and explode. I think my preference would be the Michelin over the Continental or Pirelli. But this is very much a matter of personal taste. Michelin might be the best in the wet. Pirelli probably the best in the dry. My complaint against the Pirelli is noise and vibration (on the Turbo and not the standard 996 C2). I would think in Nigeria you take whatever tyre you can find and then treat it very well. S.

[quote]Originally posted by ZBlue996Kam: <strong>36/36 is for 17" 38/44 is for 18"</strong><hr></blockquote> If you are referring to the ridiculous factory pressures, the 18's are at 36/44. [quote]<strong>Best time to set tire presure is in late morning when possible.</strong><hr></blockquote> Why late morning as opposed to early? Is air more awake then?

[quote]Originally posted by FixedWing: <strong>Actually, I've had nothing but trouble from Pirelli tyres.</strong><hr></blockquote> Your problem is not typical of Pirelli tires. I have seen this happen on several other brands.

Factory pressures ridiculous??? why is that? Wael

[quote]Originally posted by Waz996: <strong>Factory pressures ridiculous??? why is that? Wael</strong><hr></blockquote> Do a search and you will see plenty of discussion on this. Basically becasue if you set the tires at 44 psi cold, they will quickly increase to 50+psi which makes for a very greasy/slick tire. Best to start of in the mid 30's and the fronts a couple pounds less than the rear.

[quote]Originally posted by Viken: <strong> Why late morning as opposed to early? Is air more awake then?</strong><hr></blockquote> My air needs it's morning coffee or it is grouchy and you do not want to mess with it early in the morning. I agree, you must wait till late morining to check it. But if you wait too long, then it gets sleepy after lunch and it reads way too low. After 6 pm it is usually drunk and you get your gauge full of alcohol when you check pressures and the readings are erratic.

I agree completely with Viken and Greg about the factory tire pressures. BTW the S03's are the best rated tires in the wet in the comparisons I've read. Enjoy the S02's Wael, they were my all-time favorite tires, in terms of handling. Even better than the S03's in my opinion, though the S03's last me a bit longer (rear S02's lasted me 10,000Km). So make sure you keep them from getting underinflated or your really going to wear them quick.

Now i'll have to find me a good torque wrench and an accurate pressure guage.. wael

Waz996, I think it is wise to run high speed with properly inflated tires. Second, your new tires need some time to break in and it is unwise to run them at high speed. This might lead to bubbling on your brand new tires. As far as P-Zeros, I can say that I have anything good to say about them. They might be nice and great on the dry but I have experienced sidewall bubbling on not just one but two or four. I dont thinks in my opinion P-Zero is made in the same quality as Michilin.

[quote]Originally posted by Waz996: <strong>Now i'll have to find me a good torque wrench and an accurate pressure guage.. wael</strong><hr></blockquote> I wouldn't wait too long for that pressure gauge. From your description you went out with tires at ~17-18 psi cold and proceeded to drive at 150mph. You are lucky to be able to post your questions.

[quote]Originally posted by Viken: <strong> Your problem is not typical of Pirelli tires. I have seen this happen on several other brands.</strong><hr></blockquote> I only have experience with the Pirellis. It will be interesting to see what happens with a different brand of tyre and especially whether I have the same problems. I do think a lot of it has to do with driving style and the AWD with the additional power of the Turbo. Doubt the result will be the same with the C2. I personally think it very unwise to be promoting lower tyre pressures to Waz. He is living and driving in Nigeria and won't come within a continent of a race track. Rutted roads especially require proper pressure in the tyres to avoid damage to the rims. S.

[quote]Originally posted by Greg Fishman: <strong> Do a search and you will see plenty of discussion on this. Basically becasue if you set the tires at 44 psi cold, they will quickly increase to 50+psi which makes for a very greasy/slick tire. Best to start of in the mid 30's and the fronts a couple pounds less than the rear.</strong><hr></blockquote> Yup! I ran on 44 psi cold and found 51 psi hot. Boy was that an scary ride! I've got S03's all around and I now start out with 28/29/30/31 {that's LF/RF/LR/RR} and life is good.

[quote]Originally posted by pete01_996: <strong>Yup! I ran on 44 psi cold and found 51 psi hot. Boy was that an scary ride! I've got S03's all around and I now start out with 28/29/30/31 {that's LF/RF/LR/RR} and life is good.</strong><hr></blockquote> Umm... Any reason why you're running 1 psi more on the right? <img src="confused.gif" border="0">

My impression is that the left tires were heating up just a bit more than the rights. Maybe my big butt?? Or maybe just some inaccuracies in taking the pressures ... not sure. Anyone else seen this?

I must say I recently experieced this with a 2001 cabrio. Our customer complined of bad vibration around 60mph and a drift, we rebalanced and roadforced the tires, check rims for bend etc, and it just wont go away, now I cant blame the tires they are new and only 5k miles on them, it must be suspension deflection or something, our customer called the dealer they dont seem to help and I called myself and all they said is theire isnt anything else to do, If i paid 105k for a cabrio and this was going on I would sue Porsche.

O forgot this car was running Pilot Sports, 235/285 etc on GT3 rims, pressure was consistant on a 4 corners

[quote]Originally posted by Eurotek: <strong>I must say I recently experieced this with a 2001 cabrio. Our customer complined of bad vibration around 60mph and a drift, we rebalanced and roadforced the tires, check rims for bend etc, and it just wont go away, now I cant blame the tires they are new and only 5k miles on them, it must be suspension deflection or something, our customer called the dealer they dont seem to help and I called myself and all they said is theire isnt anything else to do, If i paid 105k for a cabrio and this was going on I would sue Porsche.</strong><hr></blockquote> 5,000 miles is more than enough to see these problems. As for suing, that works well in the USA but in Europe you are left with far less recourse. Best to find another way if you can. S.

Thanks everyone for advices.. I guess i'll start with cold tyre pressure of 32/34 and break them in for a 1,000miles or so.. so i dont think i can really say anything till then.. Wael

I just have a silly question: Suppose the car is known to 'tramline' or behave abnormally whenever we change new tyres.. Why then, when we buy a brand new car, it doesnt tramline? Wael 996 C2 99

The Pirelli's on my ttX50 went severely out of balance after one track day starting with factory pressures (hot rear pressure went to 58psi by my recollection) Exhaustive rebalance using the dealer's fancy new $12,000 equipment didn't solve the problem. The conclusion was that the belts shifted. Porsche bought me 4 new Conti's which have been fine from day one (no break-in). In an undamaged car, my experience generally points to the tire as the problem, not the car. Even new tires are delivered out of round, with belt separtion (see Ford explorer), and sometimes unbalancable because there is a severe weight assymetry. Remember, you can balance a square, it just won't roll properly. Off the car, you can check the wheel/tire for runout (side-to-side wobble) and roundness. Only a drive will tell if the rest of the tire is working.AS

[quote]Originally posted by Waz996: <strong>Suppose the car is known to 'tramline' or behave abnormally whenever we change new tyres.. Why then, when we buy a brand new car, it doesnt tramline?</strong><hr></blockquote> Because the effect is from unmatched tread depth front and rear. On a new car, you have the same tread depth as you get four new tires.

"Tramlining" to me means the tendency to follow tracks/ruts/camber changes in the road (which makes a bit of sense I think, as the term comes from the problem of getting stuck in tram tracks - now that would need narrow tyres ). In my experience the wider the tyre and the lower the profile the worse it will tramline, but castor and camber settings affect this also. My only experience of the rear of the car wandering around unprovoked was after getting new tyres fitted on a 968 Sport I once owned, which the bright spark at the tyre place inflated to 36F/44R (wrong for the car of course and, as they were 17" wheels, wrong even if the car had been a 911!). That made for rather more "entertainment" on the drive home than I'd had in mind

ok, so long it's not the car itself making the erratic behaviour then it's no problem! tx wael