loot87

And what improvements did Porsche make to the Turbo S and 3.6S that made them "OK" in Porsche's eyes? So far, I see nothing that makes 18 inch wheels on a 3.3 Turbo from 91 or 92 any different than an NA 964.

Adrian

The ban was issued before the 1996 model year even started. The model year 1994 and 1995 993s were later removed from the list. The 993 C4S was fitted standard with 18 inch wheels. I suspect it was just a caution whilst the C4S underwent some testing. Seeing as the ban does not apply to any 993 anymore it's not something I bothered with.
Ciao,
Adrian.

PS: It took Porsche something like 6 or 8 years to approve 9JX17 wheels for all models of the NA 964s.

Feehliks

Thank you Adrian. Two years ago a service representative in Zuffenhausen handed out a technical bulletin to me about which wheels for 993s. 94 and 95 were in principle excluded. I am sure you know about this bulletin, who elso would if not you.

If you know any further statements, etc. I would be most interested and grateful to read. I was suspecting that there is not any real issue as so many people have 18 inch on their 964s and 993s.

Best regards,

Felix

TroyN

AFAIK, the 18" restriction for 993s was addressed by the steering rack brace, which was required for (some?) '95 and earlier models.

The larger diameter wheel causes more force to be transmitted to the suspension due to the greater leverage afforded by the increased radius (force x lever arm). So I'm not sure if lighter wheels would solve all of the problem, in cases where there really is one.

tafkai

965 has different hubs , suspension etc. to a 964
maybe this is something you have missed ?????

JasonAndreas

The front wheel hubs were also updated

loot87

Tafkai,
Definately I missed it. I have Adrian's book, but haven't gone through it cover to cover yet.

Dunasso

Adrian,

You are rigt as always. The design issues are abundant, however we should not limit ourselves to only the wheel diameters. Any addition of aftermarket products alters the reliability of our fine cars. For instance, stiffer springs, lowered ride hight, heavier sway bars, urathane bushings, solid motor mounts, strut tower bracing, and let's no leave out the LWF. All of these products are simple additions that any street car could be sporting right now. All of which could and do have negative side affects. But that's what owning a prformance vehicle is all about...the un-comforts we endure to enjoy the true sports car.

Sorry for the mis-spellings,

Duncan

Adrian

Duncan,
I only concern myself with safety issues. Most of the items you mention do not impact safety the of the car in the area of reasonable probability. Safety issues are determined by probability calculations.
Sadly most people just drive without any regard to the impact of the changes they make to their car. Rennlisters only account for a very small (tiny actually) amount of car owners, even Porsche owners.
It is very easy to turn a car into a death trap for the owner, passengers and other road users.
I am sure you know that Motor racing organisations have stricter rules than most Government run motor vehicle departments when it comes to modifying cars.
Wheels and tyres are the two most neglected areas of car modifications. In reality the two most important issues for owners of any car type is looks and cost when it comes to wheel and tyre combinations. Big wheels, low profile tyres because it looks kool.
In the end the only thing between the car and the road is the tyre.
I know of people that have installed modifications on their cars (not just Porsches) that ran up bills of tens of thousands of dollars, then they fitted el-cheapo tyres. In the old days they even fitted retreads. Go figure
However, all one can do is inform. It's up to the individual to decide what they wish to do and what risks they wish to take.
I can tell you that Porsche AG took and take this wheel issue very seriously indeed. This is the only time and the only subject that Porsche issued such a warning. It also included a provision for reporting owners.
Just for the record also when the 7.5JX17 wheels were fitted to the 964 Carrera RS Porsche fitted a brace just like on the 993. It's all in the wheel and tyre overall width not the diameter. The overall wheel and tyre diameter is the same regardless of the wheel diameter. More wheel less tyre.
Ciao,
Adrian.

Feehliks

I absolutely concur, it is not the issue of the inconvenience of some stiffness, but whether "improvements" cause strucutural damages or other to the car.

I have the feeling that we are talking about two statements of Porsche:

1. Adrian's 18 inch ban list excluding the 993

2. Porsche's technical bulletin with restrictions for 18 inch on the 94/95 993

Best regards,

Felix

Adrian

Felix,
My discussions on the topic have nothing to do with the 993. They are related direct to the 964 and indirectly concerning earlier models only. I only mentioned the 993 in the cross brace as a reference.
This was first done on the 964 RS when 7.5 inch wide wheels (significantly lighter magnesium alloy I might add) were fitted along with structural and suspension reinforcements front and rear. The 3.6 litre RS was the first and only normally aspirated 964 to be fitted with 9JX17 wheels at the back. Only the 3.8 litre RS got wider rear wheels in the NA versions.
Ciao,
Adrian.

Gary R.

Good job Adrian..

Gary R.

Too much Sp lenda...

Dunasso

When you decrease component flexability with stiffer suspension components such as springs, strut tower bracing, and urathane bushing, do you NOT increase lateral load stresses on the harware that holds these components in place?
I am confused, because I am not trying to compare apples with oranges. I am understanding that there are NO adverse or dangerous side affects to add-on components other than the addition of 18 inch wheels.
I find it very very difficult to believe that this is a true hazard to be concerned with. After all, how many Porsches are out there with wheel adapters and everyone seems to have NO concerns about any adverse affects of what may or maynot be a safe range of thickness for these components. Early 911 owners have been applying wheel adapters to there car in oder to accomidate other wheel styles for years.

Don't get me wrong, I understand engineering and what a safe limit is for certain components. However, My point was, that there are many other factor that can contribute to the failure of these particular componets mentioned earlier in this thread. I really think that these failures were in combination with a number of contributing factors that may have been at limit but not beyond. With the additional contributing factor of an 18 inch rim, this limit may have been pushe too far.

With that said, I do not agree that the soal addition of 18 inch wheels will put any well maintained Porsche in hazards way.

Duncan

adsc4s

The 964 is 11-15 years old. Wheel and tire technology have come a long ways in that time frame. Based on the available wheels/tires 15 years ago, PAG did not approve an 18" wheel for their cars. Now they have 20" wheels available for the 997.

There is no reason for PAG to retest a 964 or 993 or 911 or 356 or ???? to see how a new 18", 19" 29" wheel/tire combo will work. That's old news.

As far as your Fikse and CCW wheels Gary, no one really cares what you do or do not do. Adrian is simply the messenger.