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OK, here goes....I wrote this for an FB page, but it's hard to research stuff their. Plus I was banned from a page for (I guess) speaking heretically about one of their heros. In any case, here's the article.
Hot target 28.5 to 29 psi
172 194 205 219 123 164
psi 29.1 28.9
29.1 28.8
185 213 196 176 192 168
Ok, as I was trying to point out someplace else, this is a good example of predictive tire pressures. 28.5 was the max low, 29 the max high, after 20 laps on a road course. Over 30, the tire gives up. These pressures are spot on.
Why is this important to the casual track guy?
Because, especially in a bank type of situation, or even a track like Laguna Seca, you can have a catastrophic failure.
Since I know many of you, and would like to keep knowing you for awhile longer, I thought I'd write this article.
Basically, this is called pressure mapping, and we've discussed it before on TMO. Get a notebook ( a very large one) and write down the track, date, time, track temp and air temp, then the start psi.
Run the car for x amount of laps, check the psi and raise or lower it to meet your hot target goal.
Do this for every session and write it down.
At the end of the day you will have a " map" showing the temp of air and track, it's effect on hot pressure and a predictable ( rate of rise) for that track.
Congrats, you have created your first " map".
Now do that each day, when you go to the next track you have a ballpark place to start your pressures, although the rate of rise will be different for every corner of the car, and every track.
You will also have to figure a "factor" between ambient and track temp, and that changes with every brand of tire.
If there's one thing I can stress is that cold pressures (as long as the tire is inflated enough to stay on the wheel) is meaningless, it's the hot PSI that counts.
With regards to cold start pressures.. you let the hots establish the colds. As an example you put x amount of air in the tire at 8AM at Road Atlanta with 70 ambient 80 track and you add or subtract pressure to get your target max. The next day....if everything is the same . The cold pressures are already established, just write them down for future reference. This will also give you a rate of rise...which is pretty much a constant at a particular track
So now you have a " map" of a particular day evolving from morning to evening, track temp, ambient and number of laps over several days. This should give you a fairly constant " rate of rise" for that track and that setup.
So let's say, on the last day a cold front comes through and the temps drop 20 degrees, the start pressures are no longer valid....or are they?
Go back to your rate of rise numbers, they will give you your hot PSI based on a specific psi. Just run those numbers backwards to get your starting psi for the new day.
Now those numbers will not be perfect, but after several weekends you can plot a graph based on the temp (s) and come up with your factor to predict psi / temp.
So, as an example..you know from several days that the RF will rise 10 psi over the course of 10 laps. So, it would be reasonable to assume it would be about the same from whatever psi you put in the tire RIGHT NOW, after the cold front came through.
Example 2. Over a period of 5 track days, taking careful records of ambient/ track temps you notice that the tire pressure is affected.( Let's say...they're all different) .8psi/10 degrees. So, if the temp dropped 20 degrees overnight and the tires were left alone overnight, you would expect those tires to be about 1.6 psi lower than if the temp stayed the same. (as the day before)
So.....you would account for that 1.6 psi to the RF tire, and hopefully, if you did it right, those numbers would be backed up by the rate of rise numbers.
Simple...right?
So to recap...if you get lost due to a temp change, you have 2 ways to recoup, that should back each other up.
1. The predictable rate of rise numbers that will tell you how many psi the tire will gain over time
2. The psi/ temp " factor" in this case .8 x 20 degrees equals 1.6 that needs to be added.
Take the temp derived psi number,add the rate/ rise number and you should get really close to the predicted hot PSI.
I'm warning you..there will be more..lol
Hot target 28.5 to 29 psi
172 194 205 219 123 164
psi 29.1 28.9
29.1 28.8
185 213 196 176 192 168
Ok, as I was trying to point out someplace else, this is a good example of predictive tire pressures. 28.5 was the max low, 29 the max high, after 20 laps on a road course. Over 30, the tire gives up. These pressures are spot on.
Why is this important to the casual track guy?
Because, especially in a bank type of situation, or even a track like Laguna Seca, you can have a catastrophic failure.
Since I know many of you, and would like to keep knowing you for awhile longer, I thought I'd write this article.
Basically, this is called pressure mapping, and we've discussed it before on TMO. Get a notebook ( a very large one) and write down the track, date, time, track temp and air temp, then the start psi.
Run the car for x amount of laps, check the psi and raise or lower it to meet your hot target goal.
Do this for every session and write it down.
At the end of the day you will have a " map" showing the temp of air and track, it's effect on hot pressure and a predictable ( rate of rise) for that track.
Congrats, you have created your first " map".
Now do that each day, when you go to the next track you have a ballpark place to start your pressures, although the rate of rise will be different for every corner of the car, and every track.
You will also have to figure a "factor" between ambient and track temp, and that changes with every brand of tire.
If there's one thing I can stress is that cold pressures (as long as the tire is inflated enough to stay on the wheel) is meaningless, it's the hot PSI that counts.
With regards to cold start pressures.. you let the hots establish the colds. As an example you put x amount of air in the tire at 8AM at Road Atlanta with 70 ambient 80 track and you add or subtract pressure to get your target max. The next day....if everything is the same . The cold pressures are already established, just write them down for future reference. This will also give you a rate of rise...which is pretty much a constant at a particular track
So now you have a " map" of a particular day evolving from morning to evening, track temp, ambient and number of laps over several days. This should give you a fairly constant " rate of rise" for that track and that setup.
So let's say, on the last day a cold front comes through and the temps drop 20 degrees, the start pressures are no longer valid....or are they?
Go back to your rate of rise numbers, they will give you your hot PSI based on a specific psi. Just run those numbers backwards to get your starting psi for the new day.
Now those numbers will not be perfect, but after several weekends you can plot a graph based on the temp (s) and come up with your factor to predict psi / temp.
So, as an example..you know from several days that the RF will rise 10 psi over the course of 10 laps. So, it would be reasonable to assume it would be about the same from whatever psi you put in the tire RIGHT NOW, after the cold front came through.
Example 2. Over a period of 5 track days, taking careful records of ambient/ track temps you notice that the tire pressure is affected.( Let's say...they're all different) .8psi/10 degrees. So, if the temp dropped 20 degrees overnight and the tires were left alone overnight, you would expect those tires to be about 1.6 psi lower than if the temp stayed the same. (as the day before)
So.....you would account for that 1.6 psi to the RF tire, and hopefully, if you did it right, those numbers would be backed up by the rate of rise numbers.
Simple...right?
So to recap...if you get lost due to a temp change, you have 2 ways to recoup, that should back each other up.
1. The predictable rate of rise numbers that will tell you how many psi the tire will gain over time
2. The psi/ temp " factor" in this case .8 x 20 degrees equals 1.6 that needs to be added.
Take the temp derived psi number,add the rate/ rise number and you should get really close to the predicted hot PSI.
I'm warning you..there will be more..lol
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