Ed Hughes

Well, good luck to you then. I'll bet they have a maximum speed listed as well. That, I know for a fact, does not mean you drive at or near that limit.

Again, MAX pressure is for safety recommendations, it is not a recommended operating pressure.

Who're you gonna believe? "Street Racers" or knowledge from a real race track? And by that, I don't mean my knowledge, but those that are much more experienced at navigating a 911 in anger on a real race track, not a clover leaf?

And secondly, I suppose you will continue to ignore the comments about alignment? Toe and caster have more effect on straight line tracking, camber will effect more in the turns.

I guess you car is set up well for Oklahoma.

srf506

I don't think anyone really cares what the tire guy says is max pressure on the tire. Again, that's more of a safety limit. What counts is what the manufacturer of the car, Porsche, says is the recommended cold inflation pressures for the front and rear. You can vary a few pounds up and down from this to trim out the car the way you like it to feel, but when you go too far afield you're in dangerous territory, putting all kinds of excessive strain on the suspension, steering, brakes and chassis. Its a total system designed within a specific set of dynamics and when you change one thing it all reacts to the change. Even changing brands of tires will change those relationships.

I'd start with lowering the pressure back to Porsche's recommendation, then get the car into a good chassis shop and have its alignment checked to make sure its within specs and in good working order.
You never stated if the car is bone stock, or if its been modified in anyway, or at least that I remember in the original post. How old are the tires? If they're over three years old and you've been running them at overpressure for a significant amount of time heat and stress might have prematurely damaged the tire, or dry rot might be setting in. Are the tires rated as Vs or Zs, or some other speed ratings, what about the grip and wear ratings? Are they within the range suitable for the Porsche? Sorry, I'm just not familar with a "Ventus" tire, who actually makes that tire?

Without actually seeing the tire, its hard to judge the reason other than a Porsche is an understeering monster once you're on the power in a corner. The car squats on to its rear wheels under acceleration and of course the weight shifts to the rear. This obviously causes the front-end to go light and the front wheels to push or snow-plow in a tight or high-speed turn (your clover-leaf). The tire will naturally roll-under on the outside edge. My supposition is with the high pressure in the tire the tread is trying to stay flat, the sidewall is flexing and the tire is running right on the outside edge of the tread with the rest of it off the road surface. This little bit of contact patch is supporting the majority of the car's weight at that point and its just grinding the outside sipe blocks off like you'd taken a grinder to it.

Every once in a while I'll look at something a Porsche engineer did and say "why'd they do that?" But not often, and once I think it through I usually come to the conclusion the engineers were right.

Good luck with it and let us know what you find out.

MUSSBERGER

If you were racing through clover leafs I will assume all the weight is on the left of the car. this is where you would first expect there to be tire problems. Sounds like understeer chunking from too much tire pressure.

KRA993tt

Without a picture it is difficult to know what shredding is but in general you should not be having a tire problem while driving on the street.

Is it possible that your alignment is out of spec? Possibly dried out tires or just old tires that chunked because of abuse (Heavy use). I would think the high pressures you run would just make the tires slide around a lot. After you get some new tires you may want to try some lower pressures say (34-36 or so) just to see the difference in ride and handling. In my 82sc the Porsche owners manual recommends 29 psi front and 34 psi rear.

Batman 357

Tire design has changed a lot in the 26 years since the car was built. The tires are a way different size than what came on the car. The plowing the front post seems about right. Ventus is a Korean knock off of a Yokahama sport tire. I’ll lower the pressure 10 psi and see what difference that makes.

g-50cab

Ventus as in Hankook Ventus? I have the Hankook - VENTUS RS-2 Z212

225/45/16 and 245/45/16



I run mine at 32 psi front, 34 psi rear on 8x16 and 9 x 16 fuchs on the street.

On the track I drop them to 30 and 32 and get a 6 -7 psi difference cold to hot (actually florida in the summer is more like hot to hell hot)

After a heat cycle where they get a little squirrely for 1/2 a lap they grip well. Based on both my infared thermometer and the tire wear indicators - I am using just about 99% of the tread - temps consistent all across the tire. Great tires (I actually like them better than the yokohama AVS sports they replaced) and cheaper too. I do not have any chunking - even at 110 going into turn 17 at sebring

KRA993tt

/\ /\ There you go, what he said above /\ /\

Amber Gramps

This sooo, made me chuckle. Look at the avatars that responded to the OP. I seem to get credit above and my car is in a no parking zone on a dead end with the Pacific Ocean in the background. YET, every other avatar is clearly a race/track car with owners that did more racing in there sleep last night than I have done in my entire life. Please give credit where credit is due.

Auto_Werks 3.6

If that is your car in your avatar, I would much sooner suspect that your tire is slightly catching the lip of your fender if it is "shredding". Your car looks quite low, and has aftermarket wheels, and/or spacers, which is why I would suspect rub. My old '83 used to rub only the left front fender under various severe conditions. Take a quick peek under there and see if there is an area where the paint is rubbing off, or where the bend in the lip looks a little funky. Post a pic of that tire when you get a chance!

As far as your tire pressures go... Most street racers are not the most intellegent people, and thus I try not to buy into many of their "tricks". When I was solo racing my SC I had the best results when working with pressures similar to g-50 cab (30/32 - 32/34).

jwilson95

Batman-not an expert either, but I know the Porsche manual spec is for YOUR car and the Hankook spec on the sidewall is independent of vehicle mfr./model/etc. and is solely the max pressure allowed for the car as stated several times before.

I like the idea of the rubbing as the issue because the bigger wheels/tires and a possible aging/sagging suspension on our older cars drastically reduce the potential space between tire and fender. Also, do you have any idea of your ride height vs. standard and suspension settings (toe/camber/caster)?

Hey G50 cab-

I am running the same tire sizes/widths on my 89 cab which is the 930 wheel setup in the manual. It calls for 29f/44r for the turbo with 8x9's, so that is what I have been running. I cheat a little on the front and go with 31/32 front.

It says 29f/36r for the 7x8 Carrera car. I figured the wheel width should be the determining factor at this point, not the car since it is essentially the same car without the turbo on it as far as the tires are concerned. (maybe track width is less on a narrow body vs. turbo, not sure)

I was looking at the Sumitomo's and Hankooks when I was looking for tires recently. I went with the Sumitomo's because my 993 buddy loves them vs. the Michelins/Pirellis for the buck. I like them, but I think I could easily go for the Hankooks/something else next time. With a 160 tread rating, I won't have to wait long...

PM me with more info. on them (how long/how many miles/gut feeling vs. other tires you have run, etc.) I don't like the soft sidewalls of the Sumis which give it a little more slop in side to side transitions.

Great discussion,

Jeff

srf506

I'd think if it was rubbing enough to "shred" a tire, he'd of felt/heard the rubbing, seen black rubber on his red fender lip, and smelt burnt rubber. On my 930 running at Euro height, what I rubbed at first was the AC hoses in the left front wheel well, but only on a full rack left hand turn. It raised such a racket and kicked back through the wheel enough I thought at first I was losing a wheel bearing.

Edgy01

What he said.

When you start to push the fender limits (which you clearly have with the 17s) the first point of contact is on the outer tread of the LF tire. I'm going to guess that you have never rolled that fender,--right?

Batman 357

I don’t think this is fender rub. I get a little of that on a full lock turn and you can hear the noise. I pushed the nose starting a turn a little hot and she slid some. That was the only noise.

Thanks for all the info. I may get to the local autocross this weekend. I’ll kick the pressure down some and see if I like it.

Batman 357

I've got a couple of cell phone pics. I'll take a hard look at the finder. The lip of the wearing surface has an even scrape that does not show up on the pics.

Amber Gramps

That picture has fender written all over it.

case closed. Thank you for posting the picture. It doesn't at all look like the sidewall caved under preshure, but it does look like someone took a razor to it. I was wrong all along....and to think it wasn't a preshure issue either.