What to watch on weather Data

data

water tends to slow down any car more than anything, so watch your grains of water, along with temperature, and I recommend purchasing an altimeter. You can get away with watching the baro pressure, but I've seen the altimeter change without the baro changing. It will also give you a better idea what to dial out of the box, and if you're running a multi day race, what to do if a front blows through.

Grains of water is better to watch than humidity because it's 'relative' humidity. Looking at my logbook from Foster's car, 53% relative humidity at 81 degrees is 81 grains of water while 54% humidity at 95 degrees is 129 grains. The air can hold more water as temperature increases. So dialing off relative humidity alone can be deceptive. However, when racing primarily same day events where you get a few runs to dial it in anyway, dialing off relative humidity can be pretty effective. With my old small block dragster, I could just about throw out the rest of the weather station and dial it off the humidity gauge.

That said, track temperature needs to be logged as well. If you're not running water in your block or heads, you need to monitor head temp and try to go to the line with the same head temp every time no different than you want the same water temp every time with a bracket car. I used to keep a close eye on trans fluid temp as well, and would dial the car up if it started to get warm from hot lapping.

Where you keep your weather station is just as important as the data it gives you. Personally I like to keep my weatherstation in the shade. Some of the trailer mount units are designed to work well outside of a shaded environment. More than anything it's important to keep it constant. With a handheld weather station, I think it's easier to get more consistent readings keeping it in the shade. If you leave them in direct sunlight, your reading tends to be affected by how long the station has been in the sun cooking.

You also want to keep your tires shaded/covered when possible. Many times when you're in the pit, one tire will be exposed; you need to keep it covered.

Keep very detailed records. That way after an event you can go back and look at everything to see if your car has any direct correlations to a particular weather reading or setting.

 

Will, your barometer must have been stuck. It is absolutely 100% impossible for an altimeter to change and a barometer not to change if they are both functioning. They both read atmospheric pressure the same way but just display it differently.