WillBank

OK folks here's your (collective) chance to help out someone who does not know what tire pressures allow a fine car like the 993 to handle properly...

What should I be using for front and rear?

Please no more of this poisonous repartee. If we want to spread good technical information then what is the trusted setting as it obviously differs from Porsche's (993RS's) numbers.

(And I would be really grateful if I didn't get flamed for asking the sort of question that this board so regularly solves.)

I may not know you personally but you have all helped me at one time or other so thank you very much indeed.

okindao

Viken,

You have considerable credibility on this board and frankly this discussion on air pressure has confused me. Having 18 inch wheels where Porsche does recommend 36/44 it seems you state that will cause poor handling, what is your recommendation for both driver ed events as well as day to day street driving ???
thanks

SundayDriver

I had a TT and here is what I ran (all cold pressures):

Track - 30F/32R after I had my suspension where I wanted it (tail happy). Prior to that I ran 30/34. Adjust after sessions for ~40 hot, all around.
While this was, IMO, the best handling when the car was driven hard, it is not what I ran on the street. First, I didn't drive hard enough to get the tires as hot as track and second, I feel that is too soft to protect the wheels if I hit a nasty rut. I ran 34/36. If the roads are bad around you, then you might even go higher, but you will suffer in the handling department in order to better protect the wheels.
These pressures worked for me with SO-2's, P-Zero C's, Kuhmos and Hoosiers (track only for the Hoosiers).

FYI, after getting my cars serviced, the tires were often set back to 36/44. In my C2 the car was very twitchy - I never considered it very safe at that pressure. The TT was OK at those pressures but you could feel the handling was not quite at it's best.

Anir

Mark's experience is almost identical to mine. I also run 34 / 36 cold on the street, and start with 30-32 / 32-34 cold at DE events. My track day goal is also 40 psi all around when hot. This experience covers S-02s, S-03s, and P-Zero C's, and the factory Turbo Technology and Fikse FM-10 wheels. No bent rims after almost two years of following this practice. I have a stock suspension except for aftermarket Eibach 7209 lowering springs.

DJ

I do not know what appropriate cold track pressures would be (30/32 is probably a good starting point), but I have had the most success with 37/38 hot pressures (with Kumhos). On the street, 32/35 to 33/37 cold.

Edward

Ditto to Mark and Anir's experiences with a few subtle differences:

- With the 17" Cups and Yoko AVS Sports, on the street I found that 32F/34R works very well...neutral handling w/normal wear.

- With 17" Kumho Victoracers on the track, I shoot for 36F/38R hot. I've found this to work well w/o any problems, though I don't have a pyrometer to really know. Is this too low (Mark)? Again, the car feels neutral w/good stick and nothing looks awry on the tread. Opinions welcome here.

Edward

SundayDriver

I have never run the Victoracers so have no first hand experience. I would defer to DJ on the Ecstas, as I only ran them one day - his results indicate that perhaps the Victoracers also like a lower pressure. (Of course he also bubbled the sidewalls and likes to drive sideways.)

Some tires like lower pressures than others - hard to tell without a pyrometer. You could have an experienced instructor drive your car and get their feedback as to how it feels or if you have good feel, add 2 or 3 lbs and see if it feels better or worse.

Viken

As you can see, others have contributed quite a bit to this subject. With a RWD, I think a 2 psi differential front to rear is good while on an AWD another psi in the rear tires works a bit better. Try 32/34 in your Carrera tires and see how that works. I am running 32/35 on my AWD Carrera 4S with great result both street and track.

DJ

The bubbled sidewall was most likely the result of a manufacturing defect (only one tire did this, not all four). The tire has been sent back to Kumho, and I'm awaiting their determination after they take the tire apart and figure out what happened...

No comment about the sideways bit.

SundayDriver

When I turn my head and look out the SIDE of MY car to see where I am going, I always see the SIDE of your car, so it must be the right way to drive.

DJ

Maybe, but maybe not, as that would indicate that I'm always in front of you.

993RS

Here is a question to the Porsche Club of America’s late model 911 Tech guy
and his answer:

Question: When driving on good roads (here in California they are few) I
can't hear tire noise that's anything other than what I would call normal
(fronts are 225-40ZR18 and rear are 285-30ZR18, Michelin Sport Pilots) As
soon as I get on an uneven street or highway I am shook to death and the
noise is got to be about 90dba or more in the car, let alone I get a pounding.

I appreciate that the 2002's are a lot stiffer than the 2001's and the
handling is great but can I lower the tire pressure or change some bushings
without giving up too much or little performance?

Answer: I love how those low profile 18's look, but they are really are more
trouble than they're worth compared to 17's on the street. I have friends
with a Boxster S, these are serious Porsche trackies and they still preferred
changing them in favor of 17s for street use. This is not an isolated
incident, but perhaps part of a new trend. When you consider the cost of
replacement tires, and the fact that the 17s just plain drive better on the
street, it is actually a no-brainer to swap back to 17s, assuming you can
find a set of correct wheels whose styling suits you. I can't think of many
advantages of the 18" tires actually, better looks and slightly improved
sidewall stiffness but if you aren't driving corners hard all the time, it
doesn't justify the tradeoff. And as you point out, the 2002 rides a bit
stiffer so it solves a problem we don't have. Increased brake clearance is
another reason people went to 18s, but if you aren't putting on Turbo brakes
for track use, it is not an issue. Much higher cost for replacement tires,
greater difficulty of dismounting, increased noise, reduced ride comfort, the
list of DIS-advantages builds rapidly. I still have the 18's on mine, I am
just a nut for those new Carrera 18" wheels, and I just live with the noise.
I'll trade you my winters though for some of your bad roads, any day.

Start by checking your tire pressures cold. Use a good gauge. See how yours
compare to the specs in the owner's manual or on the fuel filler cap, 36
front and 44 rear. I am going to go out on a limb and guess that yours are
not within 1 psi of that all the way around. If so, reset to those numbers,
and try your nasty roads. Then, if that doesn't help, or if it was correct in
the first place, you could try to use different pressures to work on it.
Porsche has to go with a relatively high recommendation to satisfy the tire
maker's concerns for liability and for fuel economy. The modern tires are
fussy, and with the pressure too low, the manufacturers are afraid there will
be insufficient "load carrying capacity". The risk is of a blow-out, this is
what all the trouble was about with Ford SUVs and Firestone tires. However,
overinflating any tire will increase the risk of cuts that cause leaks, so
these manufacturers walk a very fine line indeed.

You have to choose how you run your tires. If it were my car, and if I had
that problem, I would try around 30 up front and maybe 33 rear, and as long
as you stay within US speed limits, you should not be anywhere near the load
capacity limit of the tires.


Joel Reiser - PCA WebSite - 7/15/2002

I also asked Bruce Anderson, who replied: "I would stick with Porsche’s
recommendations... that is what I run in my cars.

I asked Mr Hansjorg Kunz of Porsche AG CH, who replied that "the various tire brands were tested together with Porsche, also in respect to tire pressure. For this reason, the same tire pressure recommedation was made for the various tires officially released by Porsche". He concluded that the recommendation is binding for normal street usage. In respect to track usage, to contact the various manufacturers directly. He included a German text for the German street authorities in respect to the tires, sizes and pressure.

The 993RS specification booklet mentioned in this forum specifies exactly the same tire pressure.
"

DJ

So, by posting this are you finally agreeing that everyone here was right, and you were wrong?

993RS

Read the rest please: "as long as you stay within US speed limits..." 65 mph and see the reference to the load on the tires...

JohnM

Hi DJ,

As I'm sure you noticed, that 30/33 suggestion came with the caveat , which sounds awfully like Phil's opinion when he started this thread. A flat out blast down an autobahn represents a very different tyre usage than staying within US speed limits.

Phil has clearly gone to some trouble to contact many people to try and get a definitive answer on the issue of the pressures that should be run, and much of the info he has received would seem to support his (and it would seem, Porsche's) view that the recommended pressures are a good thing if your driving is mostly street with some very high speed running mixed in. Phil (in my reading, at least) has not tried to force his interpretation on anyone and has been consistently polite in his postings, which is in stark contrast to many of the replies which (again, in my reading) have been agressive at best and downright rude at worst. Some folks on this board seem to have convinced themselves they are infallible and any opinion that differs from their own should get stomped on.