Last time at the track I was talking to some folks that do a LOT of bracket racing and have been doing it for many years. They are never more than .001 or .002 off thier dial. After they watched me break out in the second round, we started discussing weather stations and computer programs. I told them I was thinking about getting the Crew Chief Pro program this winter. They told me that they have had 3 different programs, including Crew Chief and they don't use any of them anymore. They figure it all by hand. He told me to look in the front of the Jeg's log book and it explains ratios. He did'nt tell me whether he uses one ratio or a combination of all of them? There is Corrected Altitude, Humidity, and Wind Speed. What's the difference between Corrected altitude and Density altitude? I'm guessing that corrected altitide is some of these other factors put together? It does'nt make sense to me to use a corrected altitude ratio along with a humidity ratio? Can someone please expain this stuff to me? (remember, I'm NOT a calculus major!) Thanks!

A quick, down and dirty rule of thumb for normally asperated cars on gasoline is change of .1 in ET for every 1000 feet of DA.

I know that the ratios for everybody's car is going to be different. What I was wanting to know is, do you use just corrected altitude, or do you use a combination of all of the ratios together. It seems to me, that the Crew Chief program takes all of this info and computes it all, getting much more accurate than I can. This is why I don't understand how thay can do it so accurately by hand?

density altitude, a good weather staion does the computing for you. unless your doing class racing where you have to set up a throttle stop with out a pass it's just added info. good info grant you but knowing your car and having it tuned right is more valuable to me.

Get a weather station....
There are a few out there,,,,relatively inexpensive,,,eg TAG,,,,etc.
I have used mine for the past 2 seasons,,,and it has helped alot,,,
I dont change my car AT ALL,,,,ie,,,i dial according to the weather............
I plug in the temp, barom, humidty,,etc,,,,and it calculates the DA,,etc,,,,
I record everything in a log book,,,,
Over the past 1-2 years,,,,i can tell exactly what the car will do,,,based on the change in weather,,,,only variable is the track,,etc.
It is very helpful for eliminations as well,,,,,after a few time trials,,,,i can log the runs,,,and then pick a "dial" time,,,for eliminations,,,,as the night goes on,,and the weather changes,,,,,it is very accurate,,,at least with my car....

As far as tuning,,,it's also helpful,,,eg,,,if my car is "way off",,,and i cant explain it by the weather changes,,,i know i have a problem somewhere,,,and can start looking.......



good luck,

I've been using a Tag weather station for years...
I dont know what they want to know the corrected DA,
I want to know what the engine will see and with the
tag I can get within a few thousands but you only dial
to the hundredth

The TAG weather stations are that accurate? Looks like they are about $430 from Jegs. A couple of my buddies have the trailer mounted units with the Crew Chief Pro program and the whole setup is like $1500! Would this be a waste of a $1000?

Wow,,,,$1,000 and up ?
I am just a weekend,,bracket racer,,,few times a month,,,that got tired of losing in the first round,,,b/c i couldnt run the number,,,or know where to dial the car,,,and was just guessing....
I think a TAG,,etc,,would be OK,,,

I put a link to the system i bought,,,same one as 65Racer (Davey Boyd) on the board,,,who is a great racer,,,

http://www.ifamilysoftware.com/

I think the TAG might be a bit easier to use.....

Would I be able to keep each car seperat with the Tag?

I'm looking for a new weather station myself.

So this little guy does everthing that the Crew Chief program does? This is a run log book also?

---

This isnt a log book... I still write each run down
in a Summit log book.... the Tag is a weather station
and ET predictor plus it has throttle stop settings
if you go that way(I dont use that)

Bill yes you can keep track of all 4 cars or you can
use it for different tracks... you get 4 data bases
to do what ever you want

Thanks Mike!

If we ever add a fifth car I'm in trouble though

Walk around the pits at a big event and look at everyone's weather station set ups. Some use hand helds, some rival NOAA. They all read amazingly different, some close some 500 feet dif, within 5min. The TAG unit is popular, what we use.

To begin with, a cheap 3 gauge weather station from Walmart or the local hardware for about 30 bucks, will get you in the ball park. All you are looking for is weather changes anyway, they can't give you altitude or wind speed but it usually tends to work out. My car usually picks up or slows down .01 hundreth for every 3 degrees temp change and 5 percent humidity. in other words if temp goes up 10 degrees, you are going to slow down about 3 hundreths but usually the humidity drops at the same time,so if the humidity drops 10 percent you will gain 2 hundreths so overall you would slow down 1 hundreth. Can't help with varying 60 ft but the tag can't either. I have a tag and I don't trust it most of the time, with good reason

I have a tag that I will sell.

Not that it is not a good unit, I don't trust the ET predictor. Sometimes it was dead on and sometimes it wasn't.

I just use it to record the weather in my logbook.

I use the PortaTree practice tree with the snap in weather station. I bought the practice tree first, then added the weather station. They are listed for $458 for practice tree and weather station combo. I take all the weather conditions and my run information and log it in the laptop. I also use an ET predictor and the more runs you put in the more accurate it is.

You can find used weather stations on Ebay occasionally. I just bought a used TAG unit for $150. I've only used it at two races, but it seems to be pretty accurate.