Weather ?
05-24-2004, 10:50 PM
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Weather ? Is numerically higher pressure better or worse for the track? And how do humidity %s effect HP. Sorry about the rookie ?s but this is the first time weather has actually effected my car and I need to know the meaning of all these variables. TIA!
05-25-2004, 12:02 AM
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Originally Posted by Black 99 Bird
Is numerically higher pressure better or worse for the track? And how do humidity %s effect HP. Sorry about the rookie ?s but this is the first time weather has actually effected my car and I need to know the meaning of all these variables. TIA!
humidity is water vapor in the air. The more water in the air, the more Oxygen is displaced - less Oxygen into the combustion chambers.
FOr best times, you want high pressure and low humidity.
05-25-2004, 01:15 PM
#4
Ok question about the humidity (hope this isn't threadjacking!):
Usually when I go to the track for an evening/night event, the humidity gets higher as the night goes on, although the temperature drops. So 1) does the humidity % go up only because the drop in temperature means the air can't hold as much water? and 2) is the increase in humidity offset by the drop in temperature? I'm assuming if what I said in 1) is true, then there is the same amount of water in the air, but the temp is lower, so the air is better as the night goes on.
Usually when I go to the track for an evening/night event, the humidity gets higher as the night goes on, although the temperature drops. So 1) does the humidity % go up only because the drop in temperature means the air can't hold as much water? and 2) is the increase in humidity offset by the drop in temperature? I'm assuming if what I said in 1) is true, then there is the same amount of water in the air, but the temp is lower, so the air is better as the night goes on.
05-25-2004, 05:01 PM
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Originally Posted by NHRATA01
Ok question about the humidity (hope this isn't threadjacking!):
Usually when I go to the track for an evening/night event, the humidity gets higher as the night goes on, although the temperature drops. So 1) does the humidity % go up only because the drop in temperature means the air can't hold as much water? and 2) is the increase in humidity offset by the drop in temperature? I'm assuming if what I said in 1) is true, then there is the same amount of water in the air, but the temp is lower, so the air is better as the night goes on.
Usually when I go to the track for an evening/night event, the humidity gets higher as the night goes on, although the temperature drops. So 1) does the humidity % go up only because the drop in temperature means the air can't hold as much water? and 2) is the increase in humidity offset by the drop in temperature? I'm assuming if what I said in 1) is true, then there is the same amount of water in the air, but the temp is lower, so the air is better as the night goes on.
Fact 2: Relative Humidity is the measure of how much water vapor the air can hold in relation to how much it is actually holding. relative humidity of 80% means the air is 80% saturated with water vapor. At 100%, the air cannot hold any more water vapor.
Fact 3: Ignoring other atmospheric effects such as evaporation, rain, etc. humidity will increase as temperature drops, since the air is not able to hold as much vapor per unit volume.
Fact 4: Once the temperature drops and relative humidity reaches 100%, you have reached "dewpoint" where water vapor will condense on any surface available.
So hopefully you can read these facts and see that the air is getting denser (Good), and the water vapor is not actually increasing per unit volume - the air is just losing its ability to contain the vapor as the humidity increases. If the humidity is high, hitting dewpoint is good for times since the amount of vapor in the air will also drop as the temp drops (but the track might get slippery!).
That being said, you would still ideally prefer cold temps AND zero humidity (i.e. a VERY cold dewpoint).
Last edited by Draco; 05-25-2004 at 05:18 PM.
05-25-2004, 05:16 PM
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Nice write up Draco I have always been interested in the subject. To prove the point, the other night at the track the humidity did not change from 5pm to 8pm but the temperature dropped 20 degrees and my mile per hour increased from 86.5 to 88.5.
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05-25-2004, 05:22 PM
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Originally Posted by oldschool
damn Draco! you always have the answers 
bad2000ss, that is an example of the air drying out at the same time as the temp drops - best of both worlds for racing
.
05-25-2004, 06:47 PM
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Very interesting post- I was at rock falls last saturday for a fun race that, due to low turnout turned into somewhat of a test-n-tune, as I got 9 runs in before the competition rounds, and 5 more after that!! The weather was cool but very humid, as a low front was hanging overhead. I heard quite a lot of comments about slow times, and my own times and traps were down by about .3 and 2+ mph!! frustrating as hell to be sure, but what can you do? It still beat the crap out of my best ever day at work! Good to know Im not the only one affected by it. 
05-26-2004, 04:41 PM
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Originally Posted by Bob Cosby
Draco....you sound like either a Meteorologist or a pilot? Very good, easy to understand explanation.
Bob
Meteorologist, one each.
Bob
Meteorologist, one each.
Pilot? not yet - Might go for my license next summer... I did stay at a Holiday Inn last night though!
