CSK 911 C4S

I'm going to put the C4S on the track for the 1st time this Saturday and question what PSI should I set my tire pressure?

I've been spiritedly driving the C4S on back roads and mountain roads with great results and plenty of grip with my tire pressure set to the comfort setting.

Just wondered where others have set their pressures for track day?

jlanka

This is what I remember from Watkins Glen:

Front right 33
Front left 32
Rear right 34
Rear left 31

Pretty sure it was like that. Basically low 30s, with the left rear being the lowest.

jlanka

They were checking as soon as I got off the track to see what they got up to. They didn't have a lot of 991 experience. But I think they were happy with those numbers. I didn't get the data on the "end of run" numbers unfortunately.

drcollie

On a first track day, its not going to matter. Just air them up to the recommended settings, take any loose stuff out of the cabin and remove your driver's floor mat, and you're good to go. Have fun, listen to your Instructor and don't drive faster than you are comfortable doing so.

fbroen

A fellow 991:er shared with me what his instructor at Porsche Driving School had said -- Number on the post, as hot tire reading is good. So 36 / 44 post-run.

I liked the no fuss approach, and it seemed to work pretty well for me.

Also, hot reading target is of course more consistent than trying to say x pressure cold, with so much variable going into how hot tires will be post-run.

lunarx

Leave your tires on comfort part load and you are good to go.

chuck911

drcollie is right. Tire pressure is very important, but more often than not your first time out you won't be working them hard enough to run into problems. You will probably work them a lot harder, go a lot faster, than you've ever done on the street, but it in terms of the total performance envelope still no big deal. I would however add that you should get in the habit right from the beginning of checking tire pressures immediately after each run. Its the tire pressure when hot that matters, nothing else. On that score it would also be a good idea to bleed out after each run whatever it takes to get back down to your desired readings. That way you'll learn to associate tire pressure with car handling. If you never check, or if you check but let pressures run all over the place, you'll have a very hard time ever figuring this out.

Tosilog

I run my 991 C2S on the track, 31/32 cold. It gets to about 38/41 hot. This setting is with the PZero street tires. If it is your first time, you shouldn't worry about it as you'll be busy learning the line. Just use the recommended 31/34 cold setting

paradocs98

I'm running 19" Yokohama AD08Rs. I've found that the sweet spot for HOT pressures seems to be 35-36psi front / 37-38psi rear. Things get very noticeably greasy/slippery as the pressures climb above 40psi rear.

Don't forget to air back up before the drive home, once things have cooled down after the last run. Have fun.

drcollie

If you are REALLY going to get into the whole tire pressure thing on track days, you have to get one of these and read your temps across the tread immediately on pit out measuring in three places across the tread. That's the only way you can properly adjust tire pressures:

http://www.ogracing.com/longacre-acc...-pyrometer-600

I used to do the pyro thing, maybe 12 - 13 years ago. Now I just get out there and have some fun, long as the tire has air in it, I'm good to go. And I'm an Instructor...lol

chuck911

Some basic info on tire pressures.

Every tire has a range of a few psi within which it will give maximum traction. Theoretically, on a flat uniform skid-pad type situation, there would be one exact max traction pressure. In practice though loads vary, turns vary, and so there is a range. Within that range there is no right or wrong, only your personal preference. Responsiveness increases towards the high end of the range while comfort increases towards the lower end. Anything in the 40's is too high, and into the mid-40's the car will be obviously losing grip and skating around. Anything in the 20's is too low, and the car will be wallowing around. In between, basically the range Porsche recommends, its all up to you.

Yes, it really is that simple. The only really confusing thing is all the BS about cold pressures. Cold pressure does not matter! The only time cold pressure matters is if you're concerned about your cars handling while parked.

So, to understand how tire pressure affects handling, get in the habit of checking tire pressure immediately after driving while the tires are still hot.

jlanka

Chuck, but what are you supposed to do before your first run of the day when you can't do a hot check prior?

chuck911

We had a couple times where a shop came out with mobile scales, they could check tire pressures across the tread and actually tweak your suspension, even corner balance if you had an early 911 where this was easy, right there at the track. Way cool. Checked mine, whaddaya know, all was fine! That was not always the case though.

chuck911

You run what you brung. Seriously. This is after all what pretty much everyone is doing anyway. What usually happens is you arrive with your street pressure, which by the end of the first run winds up being a little on the high side. So you bleed them off to what you want immediately after the run. Then they lose a few more psi while sitting waiting for the next run. Which you don't care about, since you don't care how your car handles when parked. Then next time you go out, when they heat up, they miraculously reach ideal temp!

Actually a bit higher. What usually happens is the track heats up, everything heats up, and so as the day goes along you're bleeding a bit each time. Eventually of course things will equilibrate, but between short run sessions and weather and track changes there isn't always time for this to happen.

By far the most useful thing I have found for getting the hang of this is to pick a pressure and then just keep checking and bleeding and driving that same setup. When first starting out there are so many things to learn, things are changing so fast its hard to keep on top of it, and it really helps to make tire pressure a constant. That way you get used to it, so that when you do decide to make a change you'll stand a much better chance of recognizing just exactly what it was that changed.

John's 991

Hi CSK,
Congratulations on your first track day! They are very fun, and can be addicting. Lots of good advice above from folks with lots of experience. I think if you try to keep your hot pressures between 38-40 psi, you should be in good shape. I would estimate that you will gain 8-10 psi from cold pressures, so can plan accordingly. As you get more experience (and drive faster), it will probably increase to 10-12 psi.

With that said, I would not get obsessed with pressures. Check them after your second run, make the adjustments, then leave them be. The first run will likely be relatively slow as you orient yourself to the track and get to know your instructor. Obviously, if something feels wrong, check them again but that should be all you need to do for the first event of two.

You will find track time to be very busy with lots to learn, and I always encourage new students to memorize the track map, turn numbers, flag station locations and watch at least 30 minutes of video by experienced drivers before going to the track. This will really help accelerate the learning process.

Have fun and let us know how it goes!