Pressure mapping Quiz

[blacksheep-1]

You ran your last session yesterday at 4PM, you have adjusted pressures to a target of 30 psi hot, the ambient/track is 85/100.

The next day the race is at 10 AM, and temperatures are 70/85 at race start. When you check the tire pressures, they are LF 17.5, RF19, LR 18,RR 21 at 60/70 degrees.

What will you be starting the race at?


The temp differential between day 1 and day 2 is 85/100 and 70/80. If you use 1 psi per 10 psi of temp, this is relatively easy. You add 1.5 psi all the way around. The only reason to note the 60/70 degree notattion is becaus eit is a temperature reference, or you want to create a "set 2" for the race. There's no reason you can't use old tires and take the pressures from them to use on a new set, I usually do that to back up my numbers for accuracey.

So, to emphasize, the difference in psi is base dsoely on the difference in practice and race temps. The cold (60/70) is only there for a reference.

So..

LF 19, RF 20,5 LR 19.5. RR 22.5 will be your starting pressures at 70/80

 

[Mad Hatter]

Boy, for an second I thought you were not going to put the answer. Felt like I was back in school again!

 

[EF1]

I need to spend more time on TGM. I wasn't even close on this one.

 

[KazarS197]

@blacksheep-1 Your day before finishing temps were ambient/track 85/100. Morning is 70/85. What if the the ambient temp and track temp are not as respectively even, both down 15 degrees in the example, to something like 70/70 Maybe it rained through the night and really cooled everything off. Now you have a 15/30 difference. Using the 10 degrees = 1 psi rule, do you go off of the, smallest drop and go with the 1.5 square, largest drop with the track temp and add 3 lbs square or add up, split the difference and end up with something like 2 heavy? Or the other way around ambient dropped way down and track maintained a decent amount of stored heat ending up with something like 30/15? I guess I'm asking which is more important ambient or track temp.

 

[blacksheep-1]

@blacksheep-1 Your day before finishing temps were ambient/track 85/100. Morning is 70/85. What if the the ambient temp and track temp are not as respectively even, both down 15 degrees in the example, to something like 70/70 Maybe it rained through the night and really cooled everything off. Now you have a 15/30 difference. Using the 10 degrees = 1 psi rule, do you go off of the, smallest drop and go with the 1.5 square, largest drop with the track temp and add 3 lbs square or add up, split the difference and end up with something like 2 heavy? Or the other way around ambient dropped way down and track maintained a decent amount of stored heat ending up with something like 30/15? I guess I'm asking which is more important ambient or track temp.

I normally use 1 psi/10 degrees because large splits are common in Florida, if the split is smaller I use .7 per/10 degrees, or even as low as .4. This gives weight to the track temp over the ambient, with the large split.
So if the temps are 70/70 and I'm shooting for a number at 80/110 (not uncommon) I would definately use the 1psi/10 degrees. If it was 70/70 and I'm shooting for 90/95 I'd use the .7.
At dusk, ambient follows track, at dawn the track follows ambient so if you are running an endurance race, you need to factor that in as well.
I got hung out with Billy johnson a couple of years ago at Road Atlanta, it is notoriously hard on the LF. The weather said the temp was dropping, the Ford engineers agreed the temp was dropping, Billy thought it was dropping and so did I.
Well, the clouds stayed away and Billy was left with a low LF tire, which is not what you want at RAtl. I corrected it on the next pit stop, but he had to endure that for 45 minutes.
Generally, a bit too much is better than way too low, I have a 2 psi window which I must hit, but a sub .5 is what I shoot for.
What is important is that you set all your pressures on all the tires that you intend to use at the earliest possible time, when ambient and track are the same, Before some crew guy opens the doors and lets the sun in, before people start wondering around and disturbing your train of thought. If you go to the races, you will always find the first guys through the crew gate are always tire guys.
As far as how much weight I'd put on the track temp, well it just depends on the track, if it is one that eats tires then it would be more important than one that didn't. hopefully, you have some notes or experience to go back on.