I have had a couple of discussions about calculating DA/density altitude for any given track. As we know the weather and the actual altitude of the track affects the out come of any given run. A car in Sacramento California is going to run faster in Maryland@MIR but will be an absolute dog in comparison running in Pueblo Colorado@PMS Raceway. With all that said......this weekend was a perfect example of what weather conditions and determining the ACTUAL DA one could claim for the conditions one raced in. So the question is......when you figure DA some calculators take into account the physical elevation of the track PLUS the weather conditions. Other calculators ONLY take into account the density of the air. I use Smokem UP and they have two methods.... Calculator 1- uses air temperature, station pressure (measure barometric pressure at the location), dewpoint. The result is the density altitude for the given weather conditions. Calculator 2- calculates the density altitude from, air temperature, altimeter setting, dewpoint, and altitude. I also use...http://wahiduddin.net/calc/calc_da.htm This calculator also takes into account the physical altitude along with weather conditions. So I ask....What is the correct way in your opinion to determine the conditions one's vehicle performs in?? .
Try this site, has the track info already in there. Pretty slick. http://www.dragtimes.com/da-density-altitude-calculator.php
Check This Using Drag Times.......So as an example on December 13th 2008 at 1:54 it shows temp50/baro29.83/humid57% =DA 371' above sea level In the same calculator I insert what the weather station by the track showed at the time temp53.7/baro29.63/humid56% =DA 860' above sea level Thats the difference.....and that is whats so confusing! .
You have two different altimeter settings 29.83 and 29.63, so that will make a difference obviously. So I guess your beef is with the temp data reported. My answer would be to record it yourself on that day and time.
Go here and buy this and you will be set. http://www.weatherbuffs.com/Kestrel_4250_Handheld_Auto_Racing_Tuning_Weather_p/ks-4250.htm I like this 1 as it gives the temps about every few mins. http://www.wunderground.com/cgi-bin/findweather/getForecast?query=91706 then click on where it say weather history of this location AS IT GIVES READINGS ABOUT EVERY FEW MIN OR SO WHERE MOST GIVE IT ON THE HR. this 1 to da http://www.modulardepot.com/density.php Some sites use dew point others humidity and i like to use humdity in the factor as thats what NHRA USES. I also use this to get the track altitudes. http://www.schnitzracing.com/Tracks/tracks.htm This is real accurate as i took an altimitor to IRWINDALE and it was rite on as the strating line was at 383 ft asl and finishing line was at 377 ft asl and the track is at 380 ft asl.
I say use the one that makes your times the fastest and put it in your sig-LOL Hey lets throw in one more equation, HEAD ON WIND, like 30-40 mph!!! Yeah I was faced with that this past Sunday and it felt like I was being held back so how do you factor that or should you simply just not run with headwind like that?
Wade heres what i found. Remember drag racing trap speed is an avg for the 1/4. S = 36.738kph for a headwind = 8.16% decrease in speed (8.9%increase in time) S = 43.401kph for a tailwind = 8.50% increase in speed (7.8% decrease in time) Convert kph to speed. 2To convert from KPH to MPH, divide the speed in KPH by 1.609344. For example, In many countries the highway speed limit is 90 KPH. This equals 55.92 MPH. For most practical intents, dividing by 1.6 is accurate enough
I use this calculator most of the time, it shows pretty much the same as drag times, but I have seen a couple local tracks where drag times have the wrong elevation http://www.modulardepot.com/density.php
This is the one I like to use it has all the tracks and weather all in one. http://www.dragtimes.com/da-density-altitude-calculator.php
