blacksheep-1
Epic Contributor
This is based on the premise that HOT not COLD, is the important pressure, no one really cares what your starting psi is, because it's not the race pressure. Hot pressures ALWAYS dictate cold.. carve that into your forehead.
At 7AM you start your practice day, the ambient/track temp is 70/70 , your target hot pressures are 32 all the way around.
So baseline your tires at 70/70 at Lf -20, Rf -20, Lr -19, Rr 19. This is for a number of reasons, the main one is so that you can dump pressure easier than you can add it, so shoot a bit high, and when the car stops in the pits, you can just dump a few psi and go back out. Generally, production cars will take about 10 laps to reach their target pressure. So run 10 laps, dump the pressure to your 32 hot target and send it back out.
For this example, you are expeected to use at least 3 sets of tires, so at 7AM when the temp is 70/70, set all of your tires at 20F, 19 R. The reason is this, since all of your tires started out at the same PSI, any changes made to the practice set can be easily transferred to the spare sets, so you don't have to go through the pressure setting routine again, if you need to duplicate the pressure on the spare sets.
Session #1
temp is 80 air/90 track after 10 laps the car comes in, your psi reading is.. Lf-38, Rf-34. Lr 33, Rr 30
This is the pressure "gain" Lf-18, Rf-14, Lr-14, Rr 11, so you dump the pressure to your hot target of "32"
So your "adjusted" psi is Lf- minus 6, Rf- minus .2, Lr minus 1, Rr plus 2 for the session.
Session #2
temp is 85/90 your pressure numbers are.. Lf- 33, Rf-32.5, Lr 32.3, Rr- 32.7, target hots are the same (32 psi) so your adjusted numbers are
Lf. minus 1, Rf minus .5, Lr-.3 Rr- minus .7
In session 3, you will be running stickers and you will need to hit your numbers right away because it is a short session,
What are your numbers on the new tires??
Well first off, you never, ever, ever, go back to the original PSI setting that you had at 7AM, Those temps are long past, if you are like most, your spare sets have been sitting around in the trailer all day and their temperature has gone up. So you get your sticker set of tires and the pressure is now..
Lf- 24, Rf-23, Lr-22 Rr25 so how do you determine pressures on the sticker set? Here is how..
Add up all pf your adjusted pressures., as an example the LF will be minus 6, plus minus 1 equals -7
Rf will be minus 2, plus minus .5 equals minus 2.5
Lr, will be minus 1, plus minus .3 equals -1.3
and the Rr will be Plus 2, minus .7 equals plus 1.3 psi
So we take the current numbers Lf, at 24 psi minus the adjusted (7) equals 17 psi
The Rf is 23 minus the adjustments (2.5) equals 20.5 psi
Lr is 22 minus the adj. (-1.3) equals 20.7psi
Rr is 25 minus the adj (+1.3) equals 26.3 psi
now if there was a large temperature variation between the sessions, we would have to figure that in as well, but for this example we're gonna just send it, It should be within a few tenths of a psi
So our starting psi for the third session is Lf 17, Rf 20.5. Lr20.7, Rr 26.3 this will give you a hot target of 32 all the way around.
How can you check these numbers?, well go to the first thing in the morning where our pressures were 20 Front 19 rear.
Add/ subtract our gains vs adjustments and we get
LF 20 + 18-6= 32 psi
RF 20 + 14 -2 = 32 psi
LR 19 +14.3 - 1.3 = 32 psi
RR 19 + 11 +2 +.7-.7 =32psi
32 psi is the hot target pressure we are seeking when the tire is at operating temperature
https://trackmustangsonline.com/member-cars/s197-mustangs.501/
At 7AM you start your practice day, the ambient/track temp is 70/70 , your target hot pressures are 32 all the way around.
So baseline your tires at 70/70 at Lf -20, Rf -20, Lr -19, Rr 19. This is for a number of reasons, the main one is so that you can dump pressure easier than you can add it, so shoot a bit high, and when the car stops in the pits, you can just dump a few psi and go back out. Generally, production cars will take about 10 laps to reach their target pressure. So run 10 laps, dump the pressure to your 32 hot target and send it back out.
For this example, you are expeected to use at least 3 sets of tires, so at 7AM when the temp is 70/70, set all of your tires at 20F, 19 R. The reason is this, since all of your tires started out at the same PSI, any changes made to the practice set can be easily transferred to the spare sets, so you don't have to go through the pressure setting routine again, if you need to duplicate the pressure on the spare sets.
Session #1
temp is 80 air/90 track after 10 laps the car comes in, your psi reading is.. Lf-38, Rf-34. Lr 33, Rr 30
This is the pressure "gain" Lf-18, Rf-14, Lr-14, Rr 11, so you dump the pressure to your hot target of "32"
So your "adjusted" psi is Lf- minus 6, Rf- minus .2, Lr minus 1, Rr plus 2 for the session.
Session #2
temp is 85/90 your pressure numbers are.. Lf- 33, Rf-32.5, Lr 32.3, Rr- 32.7, target hots are the same (32 psi) so your adjusted numbers are
Lf. minus 1, Rf minus .5, Lr-.3 Rr- minus .7
In session 3, you will be running stickers and you will need to hit your numbers right away because it is a short session,
What are your numbers on the new tires??
Well first off, you never, ever, ever, go back to the original PSI setting that you had at 7AM, Those temps are long past, if you are like most, your spare sets have been sitting around in the trailer all day and their temperature has gone up. So you get your sticker set of tires and the pressure is now..
Lf- 24, Rf-23, Lr-22 Rr25 so how do you determine pressures on the sticker set? Here is how..
Add up all pf your adjusted pressures., as an example the LF will be minus 6, plus minus 1 equals -7
Rf will be minus 2, plus minus .5 equals minus 2.5
Lr, will be minus 1, plus minus .3 equals -1.3
and the Rr will be Plus 2, minus .7 equals plus 1.3 psi
So we take the current numbers Lf, at 24 psi minus the adjusted (7) equals 17 psi
The Rf is 23 minus the adjustments (2.5) equals 20.5 psi
Lr is 22 minus the adj. (-1.3) equals 20.7psi
Rr is 25 minus the adj (+1.3) equals 26.3 psi
now if there was a large temperature variation between the sessions, we would have to figure that in as well, but for this example we're gonna just send it, It should be within a few tenths of a psi
So our starting psi for the third session is Lf 17, Rf 20.5. Lr20.7, Rr 26.3 this will give you a hot target of 32 all the way around.
How can you check these numbers?, well go to the first thing in the morning where our pressures were 20 Front 19 rear.
Add/ subtract our gains vs adjustments and we get
LF 20 + 18-6= 32 psi
RF 20 + 14 -2 = 32 psi
LR 19 +14.3 - 1.3 = 32 psi
RR 19 + 11 +2 +.7-.7 =32psi
32 psi is the hot target pressure we are seeking when the tire is at operating temperature
https://trackmustangsonline.com/member-cars/s197-mustangs.501/
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