Need help on decision

You would be better off running with hotter temps and lower humidity, but looking at that chart, it might not make much of a difference.

 

The clear answer is 9:30pm

 

I say between 6 and 7

 

The cooler the better, no question. Here's a link to a density altitude calculator:

http://www.pilotfriend.com/calcs/calculators/density.htm

Play around with it a little, you'll clearly see that the temperature is what moves it around the most, barometer is second and then humidity is last.

At the extreme, a lot of humidity is bad...but you are no where near that.

Keep in mind, the actual amount of water in the air is represented by the dew point, the relative humidity is a measure of how saturated the air is...which is also a function of temperature. The relative humidity also controls the rate of evaporation - which is obvious if you think about it.

Think of it this way, imagine a Ram with a 30 gallon tank of gas, and then a Civic with a 10 gallon gas tank. If both tanks have three gallons, the Ram's gas tank is 10% full, but the Civic's is 30% full...but both have the same amount of gas in them.

Warmer air has a larger "gas tank" than cold air does. That changes through the day...but the dew point(how many gallons of gas) doesn't - at least it doesn't really on a day when the weather is quiet.

Good luck, and let us know how it goes.

Eric

 

The later you go, the faster/cooler the air will be.

Eric

 

Assuming the track is 1500' elevation and the pressure is steady at 29.90, here are the DAs:

5pm: 3060
6pm: 2877
7pm: 2694
8pm: 2507
9pm: 2314
10pm: 2121
11pm: 1990
Midnight: 1860

Give me the elevation (or even just the name) of your track and pressure (if they forecast that) and I can give you more exact DAs. Messing around with the calculator shows that changes in humidity do not affect the DA as much as temperature and/or pressure.

 

No it does not, the air becomes more saturated as it cools at the end of the day, losing some of it's ability to hold water, therefore driving the RH up...but the amount of water in the air only changes a very small amount. It would not affect your car's performance.

Relative humidity does not equal dew point...and dew point is by far the most important number. Notice that the RH isn't even in that DA calculator I linked, but the dew point is.

Eric

 

Eric:

The Modular Depot calculator does use humidity and not dew point. I have used others that ask for dew point. Do you think that the ones that ask for dew point would be more accurate?

Sam

 

who cares just race all night man!!!!

 

Well the dew point can be calculated by knowing the RH and air temperature, so I'm sure their program just cranks that out when it is calculating the DA. The RH is a function of the dew point though, not the other way around.

Eric

 

So how did it go?

Eric

 

Do you guys all realize EricG is the on air weatherman for a major network in a major city?

I'd probably not argue with him on how the atmosphere works.

:grin:

(And shame on you EricG - why no call for the Muncie trip? I found out about it too late from CPLDaugherty, preventing me from going up.)

 

nice going wade!!!! i was going to put in my two cents on the weather, but looks like ericg handled it "decently"..........hahahahahahaha never knew that eric was a tv celeb!!! lol

 

Hey - we make it all up anyway

Sorry about the no call Matt, I feel bad. As I look at the map I see it's only about an hour for you - I know Chris lives right by Muncie. It was a total spur of the moment thing, had to ask to get out of work early and then make it back up the family for the past few days so I can only post about it now

Eric

Well more like one of those people everybody curses...

Eric