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tire pressure mapping

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I was asked on a FB page to explain how I do this so I'm sending them here. It's quite cumbersome to explain on FB.
I have been fortunate enough to work with some very talented people over the years who have brought me along. They NEVER gave me the whole answer but expected me to figure it out on my own. I will be doing the same for you. Pressure temperature curves are very complicated, they depend on track temp ambient air temp, the course, the driver, type of car etc etc. For this reason I like to start in the early AM when the ambient and track temp are the same. It will be the only time all things in the world will be equal. After the sun come sup, or goes down the variance between ambient and track will be farther apart until early morning.
This is how the info is collected, the engineer or crew chief gets one copy, I get the original.
rhjomZ5l.jpg

So, for this exercise., and let me reiterate, all these numbers are bogus.
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So we go out for session one and the results are this after 5 or 6 laps..
IowcRZ3l.jpg

We know that our hot target is 38 psi all the way around, we have established this by manufacturers's recommendation, experience or by completely guessing, so we make the changes, also noting the air and track temp.
We run another session and we have this result..
38CmXzyl.jpg

Again we now have a "map" of what are pressures are for that day and temperature, we also notice the track is biased towards the right, because our lefts are gaining more pressure than the rights, in this case it's a mustang, if it was say a Porsche these numbers, front to rear would probably be reversed, generally the heavy end of the car experiences the highest pressure increase.
IjkUm3dl.jpg

So, we can go back and conclude that for this day, at 65 degrees, what our starting pressures should be.


Now comes the question..what if a cold front comes through and the temperature drops? then you should have a formula for that, some people use 1psi/10 degrees , there are others, so if tomorrow is 55 degrees, you would add 1 psi all the way around, using that formula. Now the problem is that at some point, the tire may be so low in pressure it won't stay on the wheel (painted wheels come to mind here) in that case, you need to set the pressure at the correct temp and then find a way to warm the tires..hopefully a legal way, like placing them in the sun.
Say, for some reason you have to change tires to another set, then set the old and new sets together, out in the sun for about an hour so they are the same temps, then simply transfer the old numbers to the new tires (regardless of what they might be).
There's a lot of experience needed, stickers gain pressure differently than scuffs, for instance, different manufacturers use different hot targets, or sometimes things are out of your hands and you need to come up with a set of numbers from thin air.. then you can refer to past history. I started doing tires for Phoenix in January of 2011, I still have every pressure I have ever taken...just in case. Should I find a great setup, It goes in my happy book..
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Thanks Rob. That was on the TMO FB page.
 
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I thought PV=nRT???

Nice post! I check pressures in the morning and set em like 8 psi low all around. I just check my pressures hot off the track after 1st session. Adjust them immediately . go Back out next session and they come Back in fine. If not change by a psi and then they are good to go rest of the day. I'm not good enough for 1 or 2 psi to make that much difference lol!

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