LVDell

So I am trying to get into more of the technical side of my DE experiences to improve my abilities and understanding of how the car operates instead of "just" trying to imporove my skills. So my question is this:

What does increases and decreases from the standard 36/44 pressure do to the tire? Do I want more or less pressure?

I have been up and down this topic utilizing search and I am getting conflicting input from different threads.

FYI......my setup:
Front 225/40/18
Rear 285/30/18

Tires are SO2's on Sport Designs

TIA,
Dell

MJR911

Dell,
Since you are running street tires, you really just want to make sure the tires aren't overheating. If 36/44 is what Porsche recommends for your car, i am assuming that is where you got those numbers. Look for even wear across the service, if you'r wearing the middle more than the edges drop the pressure a pound or two. stay with them until you really begin to "chunk" them. Then its probably time for a stickier set, like Mich. sport cups. Once you run the stickier tires, there are distinct pressure ranges where the tire wants to be "hot." You then set the pressures a few pounds less when they're cold, based on how hot the day is.

You can also see suspension needs for your car a bit with tire wear. if you're not getting even wear to the inside edge of the tire, you need more negative camber. I think that is a symptom of the 996s.

LVDell

Thanks Mitch. I have recently installed the RoWM030 and what a differnce the shocks/springs/sways make! My main concern was tire pressure since I hear so much talk here on the boards but not sure what is/is not rec'd for us guys running street tires on the track. Some guys say more pressure some say less. Just can't figure it all out. I guess I will start with 36/44 (rec'd pressure for the car straight from the manual).

Thanks again for the input.


Anybody else care to chime in?
Also, what will increases and decreases in pressure do to my car on the track?

sweanders

As you drive the tire pressure will increase as heat builds up. Start with a slightly lower pressure than normal and control tire pressure every time you stop.

Make sure that you let the tires build some heat before pushing it if you start with a low pressure. And if the tires start to feel squirmy while driving make sure to stop and see how much the pressure has increased. Another tip is to only use one gauge since they can differ.

Street tires can be very sensitive to overheating so it's better to stop to many times and check pressure and temp than to risk it and do a few extra laps.

Also, check the pressure asap when you stop the car.

LVDell

Thanks Anders. Go idea to start 2-3 psi below then? Then monitor after each 20 minute session?

TD in DC

Dell,

Try making shoe polish marks on your tires (three or four per tire) running from the rim to the tread. This will show you how much is rubbing off while you are driving. If your pressure is too high, you will not rub off very much. If your pressure is too low, you will rub off too much. There are marking on the side of the tire to assist you on how much you should be rubbing off. Between using these marks, checking hot tire pressure (aiming for approximately 40 deg), and using a probe pyrometer, I found that I get the best results when I started with 29 psi all around, which is shocking considering the recommended cold pressures from Porsche. I experienced no chunking of my tires even during a cold morning, but I was careful to warm the tires up slowly.

The best advice is to ask around for the tire expert in your region, and have them guide you through this. Tom Trew from Potomac seems to know his stuff. I have been following his advice second hand through a couple of other 996 owners.

You would be amazed at the difference it makes when you get the pressure right . . . it is night and day.

Just remember to get the pressures way back up to stock recommendations (or a little above) when you drive in the District or you will bend a rim pronto. Don't ask how I learned this . . .

LVDell

Same here. Cracked a rim on my 3-series coupe several years ago

Thanks for the advice on the shoe polish. By the time I get back to DC next spring you will already be a pro

BTW, where is the area you talk about that I want the tire to be (markings on the sides of the tires)?

One more question (jeez I feel like such an idiot asking so many questions)....

What is chunking?

TD in DC

Yes, you need to mark your tires on the sidewall perpindicular to the rim with three or four marks evenly spaced. Make sure you put the marks all the way up and over to the tread so that you can see how much flex you are getting in your tires.

I have never had a tire chunk, but I understand that if you let out too much air and you are too aggressive with your driving before the tires warm up, you can rip chunks of rubber out of the tire. I understand that this typically occurs on the front tires (but could occur on the rears) around the outside of the tread. I don't know much about chunking, so someone else may be able to provide more accurate information.

No fears that I will be a pro, just check out my video

LVDell

Oh trust me.....I am not laughing. Can't wait to see the my video get torn apart after tomorrow's event

So, then is my goal to maintain a pressure of 36/44 after they are hot? If you start at 29 all around, what are you shooting for when you are at optimal temp?

TD in DC

roughly 40 degrees hot, but the probe pyrometer is also interesting to see. I am still learning how to interpret the data, because it can be a bit complicated.

LVDell

40 all the way around?

TD in DC

well, that is a rough guide. You may need to adjust based on how your car is handling (e.g., does it feel greasy, too much understeer, too much oversteer, etc. . . .)

Keep in mind that I am so much of a newbie that this is like the blind leading the blind. Ask around for the track rat with the most knowledge on this. You would be amazed at how much you can learn if you are not embarassed to ask around the track. I have no shame

LVDell

Thanks for the input Todd. I'm off to catch up on Tivo with the wifey then a good nights rest before the DE! .Just finished packing up everything in the car including suncreen this time. Leanred my lesson the hard way last time...OUCH!

911

I'm glad someone mentioned hot pressures because I can't stress the importance of taking readings for both cold & hot tire pressures. Your split seems to be a bit large (36/44). For our cars, it should be more of a 2-3 lb split. So, if the optimal rear tire pressure is 44, then I would try to bump up the fronts so that when they are hot you have a reading of 42 (and not 36).

Tire Chunking: If the tires are not broken into properly (usually happens w/ new tires) they will actually "chunk" under extreme cornering forces.

Good luck.

LVDell

Thanks Rich. I ran my tires today at about 40R and 38F. I think that may have been to little since I was feeling a bit of sloppiness in the hard corners. Those readings BTW are hot. I started out a about 29-30 cold.

I'm still learning........so thank you all for the input.

Cheers,
Dell