Ken, you are quite correct that air volume, temperature, and pressure are related. However, my point was that you cannot always arrive at the correct operating tire pressure by keeping the air volume in the tire constant, because ambient air temperature changes will affect the pressure. Therefor, tire pressure must be adjusted as temperature changes. Tire pressure is adjusted by changing the volume of air in the tire.
Perhaps an example would help. Suppose the air temperature at the race track in the early morning is 72° F, and suppose we know that the tire pressure will increase by 5° (=Y) when they are installed on the car and run in a race. Suppose also that we have a target tire pressure of 35 PSI during the race. Assume that the ambient air temperature is about the same on the track as it is in the pits, although differences here could also enter into the calculation. So we set the pressure of the new tiers in the pits to 30 PSI, knowing that they will end up at 35 PSI when they are used on the track. Later in the day, the air temperature increases to 92° F. This 20° increase in air temperature increases the tire pressure by about 1.6 PSI to 31.6 PSI. If the tires were then installed on a car and run on the track, their pressure would increase to 36.6 PSI, which is now too high. To correct the pressure for the temperature increase (from 72° to 92°), we reduce the pits tire pressure back down to 30 PSI where it belongs, by reducing the volume of air (at STP) in the tires.
Critic; volume and temperature are pressure. (see 'Ideal Gas Law') I expect that the engineers involved do indeed have exact algorithms (Perhaps from the manufacturer.) which result in the 'best' tire temperature and pressure during the race, which includes all those variables mentioned, plus driver feedback. Thus, they put the correct 'volume' in the tire before putting them in service, by tying temperature and pressure. That volume won't change because the sun warms up the tires in the pit. Now if it is also warming up the race track...
Ken, I am sure there is more to controlling tire pressures than was described in the video. It could be that the engineers know how much a tire heats up (increases pressure) during use. So, if the tire has a pressure of X PSI when it is just sitting in the pits, ready to be installed on the car, then it might have a pressure of X + Y after a few laps when it comes up to the pressure goal. Since Y is known, it is only necessary to control X by maintaining the tire pressure while the tires are in the pits. If the day gets hotter, then some air must be let out to maintain a constant pressure (X), and this would be true of tires that are being used as well.
The goal might be to maintain constant pressure (X + Y) with temperature, which means that X (pressure) must be held constant. It would be undesirable for tire pressure to increase with temperature.
You seem to think that it would be desirable to hold the VOLUME (at STP) of air in the tire constant by allowing pressure to increase with ambient temperature. Interesting theory, but I think pressure is more important than air volume when it comes to tires.
Beth, and sometimes really big details! Last weekend at Texas, the KV Racing team could not get one of thier cars started...Rubens Barrichello had to settle for a 24th place and DNS (did not start). I wonder if that ever happened to him in his 19 years of F1 racing?
I watched the IndyCar race at Texas last Saturday evening...good race! My race track preference is high-banked ovals for great side-by-side racing all around. It almost looked like Graham Rahal would win, but slid up the track and brushed the wall (push...aka understeer), allowing Justin Wilson to pass for the victory. Perhaps if Rahal's tires were in better shape at the end of the race, he may have won?
Yes, a lot of tire management involved during the race. Another tire factor is for the driver to take care of his/her tires when racing. If a driver runs very fast laps, the driver can "use-up" the tires on the car, and not have good grip left when it's really needed, such as the end of the race. As they say in car racing..."tires are everything"!
I'm kind of mistified as to changing the pressure because of the sun heating up the tires, while still in the pits! The only temperature and pressure of concern is when the tire is in the race, and I'd expect that to have it's own dynamic. (Which would encompass weather, track, race, mechanical, and tire tuning conditions.) When pressurizing tires in the pits, I'd think you would get an infra-red thermometer reading of the tire, and compensate tire pressure accordingly, i.e. less pressure for a cold tire, more for a hot tire. Then when they are in the race, they always end up in the place you specify.
I suppose it's the celebrity thing. Think about all the people who pick through trash just to get their hands on some piece of clothing or discarded item that belonged to someone famous. Not to mention what they might be able to command on eBay for an item that has ties to a winning race car.
I agree, Beth. It's amazing to hear that they have to keep security guards nearby, not only for matters that involve competitive advantage, but to provent people from taking their tires and turning them into coffee tables.
It's crazy how far people/companies will go to get their hands on the secret sauce. I imagine there are tight protocols for keeping these cars and components locked down at night. Listening to these clips really gives you the sense that it all comes down to the smallest of details in terms of making a difference as to who wins or loses.
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