Definitely going to try to make what I can
So many variables... and the final PSI can change with different vehicles, tires/wheels (different tires of same size can run different psi), daytime temperatures, weather conditions ... the main decision is per event... street, highway, pylon autocross, hi-speed lapping (HSAX/HPDE). For performance driving (AX.HSAX, etc)... always increase a little vs daily driving. Where the heavier weight is (front engine)... run 2-4-6 psi higher than rear. Example street/hwy... front 34, rear 32..... AX/HSAX front 40, rear 36.. (some cars/tires etc... f 45, r 40, etc). You can also dial in understeer/oversteer/nuetrality.. experience and multiple events will tell you that.l
Look at TIRE RACK web site as they offer some recommendations.
For competition events, the chalk or shoe polish is a good practice, as well as temp measurements.
What Mitch and I are saying is, if you are in competition, you can't be satisfied with a "Oh, it's AX day and I'll run 4psi more than Mfr's recommendation... or "it's Track Day so I'll run 6psi more". That's just pure guessing.
For competition - You want as even temperatures as possible because this implies your tires are contacting the pavement with equal traction. Uneven temperatures means the hotter areas of your tires are working harder than the cooler, and you're not getting full grip from the cooler parts of your tires. My temps range from 102F to 125F measured in the 'valley' of each tire's tread (which is a good location to measure because the 'valley' holds a temperature better than the contact surface which is affected by the pavement your car drove over after coming off the track). Either way, map your temp measurements from the same spots consistently each time you come off the track. I'm usually able to get within 5F, and on a good day within a 2F temperature spread, and I know from years of tracking my ideal temps are always near 41psi HOT right off the track, plus or minus 2psi.
So, try a baseline pressure, get out on the track, and AS SOON AS PRACTICAL when you come off the track, make a chart of the tire temperatures across the face of each tire and take your tires pressures. Gather the data first and read it afterwards. You want a "map" of your tires' temperatures and pressures so you can read what the data tells you to do about it.
What do you read?
Something like 105-118-109 = High in the middle = Needs less pressure.
Something like 120-111-122 = Low in the middle = Needs more pressure.
Try 2-3psi increments.
After you're confident mapping and adjusting tire temperatures, you can look at side to side temperatures to read what your alignment needs to be:
Something like 105-109-114 = Clearly hot to one side = Adjust camber to put more weight on the cooler temperature.
With a car aligned perfectly "symmetrically" driving on a left turning track, you'll often find the right side temperatures to be hot on the tires. So reduce camber on the driver's side tires and increase camber on the passenger side.
What you want out of it will dictate how much time and effort you put into tire pressures.
If you are just starting out, I'm guessing you could gain 0.2 - 0.5 seconds per 60 seconds of lap time.
Tweaking alignment will bring gains too, but means scheduling with a shop or bringing dedicated equipment, which is another level.
Cheers,
- Art
