San:
Chalking the tires is a good trick for autocross or DE, HOWEVER:
1. Chalking the tires before they're warmed up isn't advisable. It's going to give false readings. If you fill tires to 30 psi cold, the tire will go pretty far on their sidewalls until they warm up. Better to do this after the tires are hot. That's when you want to have the tires just right, not while they're cold at 30 psi. Once the chalk is gone from the cold tires lap, it can't tell you anything that's true. You'll be putting too much air in the tires.
2. The structure of most DEs doesn't allow time for that sort of stuff during sessions. To do it right, you'd have to do a couple good hot laps and have tires up to temp, then pull into hot pits and then get out of the car and mark all 4 tires. If you can arrange it, fine. For beginners, there are far bigger fish to fry like learning the track, learning what an apex even is, what the difference between early and late is. yadayadayada. So, if I were the instructor, I'd have to have pretty high confidence in the student. Then I'd want him to talk over his plan with me prior to the run. To do this in a valid way, the tires must be at full temp before you mark them....Then go out and do your laps, then read the chalk marks.
3. That said, I'm not opposed to starting the first session with 30 psi in each corner. After a few hot laps, most tires will increase in pressure 4 to 10 psi depending on if it's the corner doing the most work or the one doing the least work. For front wheel drive cars, the fronts do almost all the work, so the delta of pressure increase can be even more.
You check the tires hot at the end of these laps, or at the end of the session. If you then set your hot pressures at 34 to 36 psi, (all the same pressure but which exact pressure depends on the tire used, the amount of negative camber, the accuracy of your tire gage etc.)
My car with MPSS or Hankooks, my camber settings and my tire gage works well at 36. Much higher and the tires start to slip around too much. Too low and they'll blister from too much heat. I've noticed, when they get up to about 39psi, they start to feel greasy and the car is difficult to drive quickly.
What I'm trying to say here is that all these sorts of methods have their place at some point in learning your car and your tires, but that for the infrequent adventurer or the new guy, a lot of complicated procedures is too distracting from the business at hand. Keep it simple, get in the ball-park. Get your laps feeling good. If I can get two perfect sessions, where the car and I are in synch and I get all the turns as intended, smooth, connected, fast and right at the limit out of a weekend, I feel pretty good.
So here it is again...simple:
1. Set all tires at 30 psi (this part isn't critical...read on to see why)
2. Do two or three pretty hard laps. They don't have to be prize winners but you have to push sufficiently hard to get the tires up to temp. That's not possible for Novice group guys...So you newbies, just set all 4 at maybe 32 psi and do nothing but learn the other stuff for two sessions....then start adjusting for hot pressures..
3. When you feel you've got the tires hot, pull off the track to a safe place (hot pits or wherever the officials tell you), turn off the car...DO NOT put on the hand brake. Put the car in gear with engine off. Get out of the car, pull out your handy pocket sized tire gage, check the left front. Drop psi to 35. Check left rear. Drop psi to 35.
Check right rear. Drop psi to 35. Check right front. Drop psi to 35. Get back in the car and go back out for the remainder of the session. The car should feel a lot more dialed in.
4. After the session, Check them again. Drop pressure as needed down to 35psi. Hopefully, you won't have to add because that's inconvenient!
5. Let the car and tires cool down. DO NOT RECHECK THE PRESSURES. Re-torque the lug-bolts if you're looking for something to do.
6. Go back out and run your next session. If the car starts to feel slippery again, go back to the safe place and drop the hot pressures to 35 again. This often happens because a. When the tires feel good, you go faster and that heats them up more. b. As the day goes on, usually the track and ambient temp goes up and that heats the tires. If you heat them enough so they're approaching 40 psi, they're probably going to feel slippery.
7. If it rains or becomes cold, you may need to add air. It's good to have a compressor so you don't have to stand in line for track air. You can guesstimate the change in air pressure, but then when you come in, check your guesses.
Here's an example of that scenario: I'm in B Group. After lunch, A Group went out in a light rain. It's still cloudy but not raining anymore. I know the track has cooled. The temp is 10 degrees lower than before.
Check the cold pressure of each tire. Add 3 psi to each one, wherever it is, before you go out. At the end of your session, check hot pressures again and adjust as needed.
8. Make a note, mental or physical, of the HOT pressures when the car works the best. That should be your target pressure for all 4 tires next time.
9. Don't think about cold pressures until the day/weekend is done and you're going home. If you're driving on the tires you ran, you'll want to let them get as cold as possible while you pack up, then put something near your normal cold street pressures in them. If they're still a bit hot, you can use a lower pressure ...~1 psi for each 10 degrees that the tire/wheel is hotter than ambient. You'll have to guess. When you get home, check set them when they're really cold before you drive on them again.
10. Monitor your tire wear. If the track is clockwise, the left side will be doing more work. Generally, the fronts are the ones that get the most wear. Consider rotating the front tires or both tires from side to side. It's good to buy non-directional tires for this reason.
This system isn't perfect, but it gets you close enough to do good solid laps, feel a connection to the track and the car and have a good time without spending your whole day on tires. There's a lot of other things to do and learn.
If you ever go to a free-lapping day where the track is open for the day, you can play with chalk and tire pyrometers and all other sorts of fun toys, but when you're learning how to drive the car, try and just learn how to drive the car and not distract yourself with the pursuit of the perfect tire pressure. Likewise, if you go racing and you manage to have a pit crew, you can put them to work an all sorts of good stuff. There are many books on this. Most guys have a system and it's good to have a system. I've tried a lot of them. In the end, at a track day when you're not racing, this will get you close without a lot of pain.
:cheers: