winders

I am stealing my wife's 997 to do a couple of DE events. What tire pressures should I run with Continental ContiSportContact 3 tires? Fronts are 235's and the rears are 295's, both on 19" wheels.

I am looking for better tire wear; ultimate grip is not the goal.

The forecast suggests that it will be right at 60 degrees.

Thanks,

Scott

Joe Weinstein

Better tire wear at a DE event will be more a function of your alignment than your
tire pressures, within the range of acceptable pressures... Just aim for the pressures
that Porsche recommends when the tires are hot, which means you should start cold
with the pressures 5 pounds or so lower, and see what they are like at the end of your
first session.
If you can buy/borrow/rig-up a tread-depth indicator, check your tread depths at
the end of each session. If your alignment is close-to-stock, expect that your outer
third of each tire will be going down more than the rest of the tread.

utkinpol

follow what porsche manual says for stock street tire pressures when you use your street tires. start with 33/39 cold, after first session quick check tire pressures and make sure they are within allowed range. usually stock street tires do not hold very well if they get above 45psi rear.

when I drove my car in stock class on stock tires i kept hot pressures 32/36 but AX is not track and it is probably far from ideal.

if simplified wear rules are: more pressure - less wear. with too much pressure you will start wearing out center section of a tire. you really will be better keeping pressures close to what manual says until you figure out yourself how to play with those.

savowood

Check with Continental on the recommended operating pressure. Typically you'll find they like the 36-40 psi range. The number on the door is not what you're looking for. For optimum wear and performance, the pressure when hot should be in the range recommended by the manufacturer.

mark kibort

start out at 30psi cold ,more so because you have 19s. you dont want to be much over 35psi hot on a street tire with a very short sidewall.
as far as wear and handling. if its handling better, it will be wearing less (for a given pace).
the guys that run 40psi, are usually all over the track with scatey cars. the recommended pressures from porsche are for MPG, not handling and usually are the max allowable pressures, not target pressures.

Mark Dreyer

I can always tell when my tire pressure is too high as the car jumps around a lot on hard braking. I start cold at 29 all around which translates to 35 hot.

Coochas

On my 997TT which has similar sized tires as your wife's car I start pretty low with 27F and 31R. On a 60F day I would probably add a few pounds more cold. I have the Bridgestone street tires (which suck). I ran similar starting pressures on PS2 on my old 997C4S as well. When most of these street tires get up to 40 psi they get pretty greasy. Then again, when you're at PSDS they typically shoot for the pressures all around in the mid 40s. I believe they do this for improved tire wear.

IcemanG17

I like to run street tires as low as possible......for example the Dunlop Direeza's that we raced Lemons on were HORRIBLE at 40psi (hot)....super skatey and just sucked....the exact same tires at 34psi felt like they had twice as much traction..... I like to go out cold at 30psi and adjust after the 1st session...since they can jump 6 psi....

Bob Rouleau

Aim for 36 lbs F, 38 lbs Rear when HOT. Start at 32 F 34 R cold and check when you hit the pits after the session. You will probably have to bleed out some air to hit the target pressure. Never let the rears get over 40 - the rear of the car will be loose.

Regards,

certz

+1 to Bob Rouleau and savowood - at least, that is my experience with street tires as well.

renvagn

Ditto for what Bob said. What I tell my students.

todinlaw

I sat down with a tech from Hoosier not to talk about Hoosier tire pressure, but tire pressure on street tires. I was doing some research for an article I wrote. the short answer on your car is about 45 lbs hot in the rear and 42 in the front. Here is the longer story. Street tires are not designed for the loads of racing. the sidewall of the tire states its max pressure don't exceed it but you can get close to it.

As you increase the air pressure of a street tire, its like adding spring rate to the suspension it firms up the suspension and it can better handle the loads of the track. If you under inflate a street tire, that generates heat, it will cause excessive wear and will cause a loss of traction when the heat gets to a certain point. If your tire starts clunking that is excessive heat due to not enough pressure.

Some my think that if you run high pressures it will make the tire slick, due to crowning of the tread. that will not happen with today's belted tires. they will not crown with in the max pressure range. So there is more upside than down side to running higher pressure in street tires.

This is from a Tire engineer. It made sense to me.

Steamboat

I sent this message to Bridgestone early this year:

Message: Greetings,
I am running Potenza RE-11's on my 2008 Porsche 911 Turbo and would like
some guidance regarding pressures for track (HPDE) events.

When starting at the manufacturers recommended pressures of 33f/39r, they
regularly see a gain of 8-10 lbs after a 25 minute (summer) session which
seems to produce a greasy feeling and one in which the tire seems to be
"going away". As a result, I tend to bleed the pressure back down to about
35/40 which seems to help. Some drivers seem to think this is an unsafe
practice.

I would be appreciative if your engineers would weigh in on this topic. Is
this practice okay? Should tires not be bled at all based upon design
considerations? Should the tires initially be set well below the
manufacturer's recommended cold pressure settings to compensate? Or is there
something else?

Thanks for any advice you may be willing to provide. Best regards,

Their reply:

On the track, the tires are obviously doing a lot more work than when you're
driving on the street. It would be acceptable to run lower than the
manufacturer's recommended pressure and/or bleed the tires down to get the
grip level where you need it to be. The best way to get your pressures is
to start with a baseline pressure, such as manufacturer's recommendations,
then measure the temperature across the tires when you come off the track
with a pyrometer. If the tires are hotter in the center, the pressure is
too high. If the edges are hotter, then the pressure is too low. You
should adjust pressure up or down accordingly until the temperature measures
relatively the same across the tires.

I hope this helps.

Bob Rouleau

Todinlaw - a Michelin tire engineer told me that street tires are formulated to work best at pressures a little below 40 lbs hot. Ten years experience as the Chief Instructor of my region has shown over and over that pressures over 40 lbs make a Porsche unstable in braking and cornering. Note that Hoosier DOT tires generally require higher pressures than regular R compounds and perhaps that influenced his answer. I can say that Michelin, Continental, Dunlop, Pirelli, Sumitomo, and Yokohama all like hot pressures in the 36F 38R range on a 911.

Regards,

todinlaw

Bob I think Steamboats response is the most accurate the only way to tell the right pressure for that car, that tire, that day, and that set up is with tire temps. we are all talking hot temps. Bluntly I do not trust most, not all but most of the MFG recommendations on pressure for street vehicles on street tires because there considerations for tire pressure has to do with ride, and comfort. Not all the time but much of the time. Porsche might be excluded. but if this is a general discussion then I would caution about relying on the MFG recommendations.

I would have to see the tire temp between the 38- 40 range you mention and the 45 I suggested on a pure street tire, that would be interesting. I never ran street tires on my GT3 so i can not comment on my experience with streets only what I have been told.