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Racers' Guide to Weather Monitoring

As important as reliable instruments, equally vital to a racer is information. If you don't use your weatherstation correctly you might as well be guessing. From 1990 through 1996, until the cost became prohibitive, Altalab published and distributed a FREE quarterly newsletter for racers which covered many tech topics. Much of that information, ** PLUS NEW ARTICLES ** is reprinted here.

This is a living document, email us with your questions.
Copyright 1990-98 by Altalab Instrument. All rights reserved. Unlimited permission to copy or use is hereby granted subject to inclusion of this copyright notice and our World Wide Web URL: www.altalabinstrument.com/

Glossary | FAQ | Tech Articles

Frequently Asked Questions

Choosing a Weatherstation

What should I look for in a weatherstation?
How did early drag racers measure the air?
Do I need fan aspiration?
What do you recommend for Kart racing?
What do you recommend for Junior Drag racing?
How does your weather station compare to others?

Gauge Placement

Where is the best place to put your weather station?
What are the worst mistakes racers make in gauge placement?

Understanding Weatherstation Readings

What information does your weatherstation provide?
Why doesn't Altalab Instrument use an O2 sensor?
My weatherstation doesn't match the other guy's.
Do I have to recalibrate my barometer at each different track?
Can I call the airport to check calibration?

Drag Racing Prediction (CliMax 3, PCM and Merlin Software)

How does your system handle alcohol cars?
Doesn't Altalab have special programs for Junior Dragsters?
Can your programs predict more than one vehicle?
I like to run the car lean, will your computer still predict it?
I don't have time to use the CliMax 3 graphing sheets. Are they really necessary?

AltaCom II and Weather Telemetry

Do I have to use a PC?
I don't have a serial port, can I use a usb port?
Can I run the weatherstation from a 12 volt supply?
If I get the Alta can I upgrade to paging later on?
Will it hurt the remote to get wet?
Should I build a roof or sunshade for the remote?
Do you supply mounting hardware for the remote?
Can I get extra pagers for AltaCom II?
What if someone else has an AltaCom at the same race? Will it mess up my transmissions?
Can I predict more than one car?
Is wind speed factored into the live predictions?
How many runs are needed for predictions?
Can Merlin predict a Jr. Dragster?

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Choosing a Weatherstation

What should I look for in a weatherstation?

Select a weatherstation that is specifically designed for racing. An off the shelf instrument, no matter how accurate may not perform well in the racing environment. Gauges you buy from a department store are probably designed for indoor use, and will only be accurate during a narrow temperature range.

Look for a weatherstation that offers some immunity from IR Heat through its design. For example, in our weatherstations we put our temperature and humidity sensors inside the case, not sticking out. This shields them from direct sunlight. We chose a light colored case, which is slower to gain solar radiation than a dark case. In addition, fan-aspiration is either standard or an option on all our weatherstations. If you have fan-aspiration, the movement of air will both prevent the sensors and case from heating up, and promote best response to ambient air changes.

Look who you are buying from. Can you get information if you need it? Is the sales staff knowledgeable? Do they take time to answer your questions, or are they too busy to listen? If they don't talk to you now, don't expect them to work with you if you have questions later. Can you call from a race on the weekend and get tech help?

Find out what kind of tech support is offered. What kind of manuals come with the weatherstation or software? Are they written for the average reader, or do you need to be a rocket scientist to make sense of the material? Or worse, is the manual useless instead of being chock full of tips and techniques you can use? Also check out what kind of warranty you will get with the weatherstation.

How Did Early Drag Racers Measure the Air?

Bob Hoffa, Altalab Instrument's President, interviews "Big Daddy" Don Garlits.

While researching the origins of air and racing, Don Garlits told me what he did back in 59 or 60 with his early nitro efforts. He had a pack of birthday candles and a fishbowl for a weatherstation . Say what? It's true, he'd light a candle and placed a fair sized fishbowl over it. As we all remember from science class or Mr. Wizard, the candle burned out after a period of time because it consumed all the available oxygen. If the candle could produce a flame of the same rate of fuel consumption every time, the quantity of oxygen could be determined by measuring the amount of time elapsed until the flame was snuffed. Very elegant technique. Mr Garlits is an innovator and genius and this story set the tone for gathering other interesting techniques. What he did is the same every racer has tried to determine in one way or another. You have the fuel and the machine, how much oxygen is available to oxidize that fuel and produce power?

Do I need fan aspiration?

The benefits of fan-aspiration cannot be overstated. Altalab pioneered fan-aspiration for motorsports weatherstations because the benefits are so important. The fan pulls air across the sensors (or gauges) so they can measure the ambient air, and the fan also prevents the case and sensors from overheating in direct sunlight. All our weatherstations have the fan as standard or optional equipment. See IR Heat for more information.

It is possible to get good weather readings without the fan, but it is more difficult, especially if you need a portable weatherstation. Drag racers who want to take their weatherstation to the lanes must be careful to provide shielding from sunlight and must look for a suitable spot to take last minute readings.

What do you recommend for Kart racing?

The Delta ACE weatherstation is specifically for air cooled engines. It provides all the information needed for tuning to maximize performance and prevent engine destruction. It comes with sample 2 cycle log sheets and instructions, so you can best establish a baseline of vehicle performance.

What do you recommend for Junior Drag racing?

The Delta ACE weatherstation is ideal for juniors. It provides all the information needed for both predictions and tuning. It comes with graphing sheets and instructions, so you can predict even without CliMax3 or our PC program.

How does your weather station compare to others?

Isn't this the sixty four thousand dollar question! If you are hoping we will trash our competition, 'fraid not. Read our answers to other questions and study the glossary. That will give you a sense of who we are and how we build our weatherstations. You can also check out what our customers have said about us.

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Gauge Placement

Where is the best place to put your weather station?

In the best of all possible worlds, your track would have AltaCom TDS and you would have weather data on a pager transmitted directly from the racetrack. Second best is to have AltaCom II mounted at your trailer with the fan-aspirated sensor housing elevated above your trailer roof. All you have to do is read information from the pager.

But for a handheld weatherstation, or a set of analog gauges, you have to make more of an effort to get reliable readings. Stay aware of the location of your weatherstation and provide shielding from sunlight and IR Heat. If your weatherstation is not fan-aspirated it must stay in the shade. Placing the weatherstation under the gooseneck of a trailer is usually a good place, as is the wheel well. (You might want to hang a "remove before flight" tag on it to prevent the obvious.)

Provide good air flow. Place your weatherstation in a lawn chair so air can circulate around it. If you use a pit fan place the weatherstation where it will get the benefits of air movement. You can place corrugated cardboard between your gauges and objects that may be radiating IR Heat, such as trailer walls, asphalt, or air from a generator.

Don't hang the weatherstation too close to the awning. Even a light colored awning will heat up in the sun. In addition, since hot air rises there is likely to be a pool of warmer air just under the roof, particularly if the awning has side walls that trap air by preventing air flow.

If your weatherstation is fan-aspirated so much the better. Keep in mind that even a fan-aspirated weatherstation must be protected from IR Heat. A classic mistake would be to have the fan running full tilt with the weatherstation sitting on a 120 degree car hood. The fan will pull that hot air right across the sensors. That's why our Alta remote sensor housing is supposed to be mounted at least 4 feet away from the trailer roof or walls.

If you take your weatherstation to the track you should provide it with shade, and pick a spot where you'll take your last minute readings. Get off the asphalt and go to the shade of the tower. Better yet, if you can get to a spot downtrack away from the other cars.

What are the worst mistakes racers make in gauge placement?

Putting gauges inside the trailer where the air can be different than outside is common. Another common mistake is to hang a weatherstation on the exterior trailer wall or door, even under an awning. If even part of the wall is baking in the sun, your weatherstation can pick up extra heat that is not relevant to air temperature. See IR Heat for a detailed recommendation.

An obvious mistake is having the weatherstation in the sun (unless it is fan aspirated). We heard one racer say, "Well, my car is sitting in the sun so the weatherstation should be there too."

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Understanding Weatherstation Readings

What information does your weatherstation provide?

All Altalab weatherstations provide Temperature, Relative Humidity, and Absolute Barometric Pressure which are measured by sensors, and Adjusted Altitude, Absolute Humidity and Dew Point which are calculated from the sensors.

DeltaLite and Delta Hi also provides Vapor Pressure and Grains per Lb.
Delta ACE also provides Air Density Ratio and the ACE Factor.
Alta and AltaCom II also provide Vapor Pressure, Grains per Lb, Air Density Ratio, and Density Altitude. Link to brief definitions of weather station readings.

Why doesn't Altalab Instrument use an O2 sensor?

Altalab Instrument pioneered the use of the O2 sensor when we released the 02 ALTA in the Fall of 1994, but gave it up after 1 year because it had more problems than could be justified by the value of information gained. The four main reasons for our decision are listed here.

1) Current technology 02 sensors function like a battery, and slowly drain down over their lifespan. They need annual calibration in order to remain accurate, particularly if the racer wants to build upon previous performance. Also, they have non-linear output, so to compensate we calibrated each sensor individually and generated from 6 to 10 calibration points per sensor. Most racers do not want to be bothered with an annual calibration, and their ability to relate current information to past references thus degrades over time.

2) The current technology O2 sensor contains an electrolye, and poor temperature compensation. When overheated heated, such as would happen on the dashboard of a car, the readings could go haywire and could take HOURS to settle. Altalab does not consider this acceptable in a portable instrument designed for motorsports. Our 02 Alta (like our current Altas), was trailer-based with fan aspirated sensors.

3) The O2 sensor currently available has a 1% accuracy rating which sounds pretty good until you realize that this means 1% from 0-100%, not 1% of 20.94 (standard O2 %). You could have an arbitrary fluctuation from 20.54% to 21.54% and still be within spec. This is NOT useful or reliable information.

4) Perhaps the most important reason - In all the testing and weatherlogging with the 02 sensor over a 2 yr. period, and after studying data from more than 20 different weatherstations we did not find significant correlation between 02 measurement changes and performance changes. The biggest changes in 02 measurement were caused by temperature fluctuations.

My weatherstation doesn't match the other guy's.

There are many reasons your weatherstation may not match someone else's. Different weatherstation manufacturers use different formulas to calculate both measured and calculated values. A digital instrument may have a different range than analog gauges. Some weatherstations are designed for racing while others are desktop instruments. Or, one weatherstaation may need calibration.

You should expect accuracy in your weatherstation, and if you suspect miscalibration get it corrected. Keep in mind that some important aspects of weatherstation performance such as repeatability, cannot be determined through comparison. The final test of any racing weatherstation is whether or not it is working for you, allowing accurate predictions and reliable tuning.

When comparing your instrument to someone else's be sure to let the weather stations settle in the same location for 10 minutes or so before checking the readings. If a friend's weatherstation has been in the in the sun for 5 minutes, and you try to compare it to a weatherstation that's been in the shade there will be a difference caused by those different conditions. See Response Time.

Be specific about what readings are different. Let's look first at the measured readings.

A difference in barometer reading could be caused by:

  • One is absolute and one is sea level.
  • Some companies scale their digital barometers light by 25% over full scale range. We don't. You would see more of a difference at higher altitudes.
  • Some digital barometers may not have adequate temperature compensation, so if you are comparing them at high or low temperatures the uncompensated barometer will read higher.
  • Note that an analog barometer may have drifted due to vibration or being bumped, but it will still show the same amount of change even it an incorrect setting.

A difference in temperature could be caused by:

  • The gauges have not settled together long enough. The larger and heavier the instrument, the longer it will take to settle.
  • Comparing at too extreme a temperature. A desktop model will not be accurate at the highs and lows. Some digital temperature sensors are less linear than other types.

A difference in relative humidity could be caused by:

  • One point versus multi-point calibration. Altalab provides multi-point calibration to keep the RH sensor accurate full scale, some other instruments are calibrated at only one point. Think of this as trying to keep a long heavy board level. It's much more reliable to use multiple supports than one.
  • Difference in sensor accuracy.

If the measured readings are different then it is likely the calculated values will also be different, after all, the measured values are the starting point. The biggest difference us usually between weatherstations that provide Adjusted Altitude and those which provide Density Altitude.

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Do I have to recalibrate my barometer at each different track?

Altalab weatherstations use an absolute barometer instead of a sea level corrected barometer. By using absolute, you do not need to recalibrate at every new location, and you don't need to know the elevation of the track. A sea level corrected barometer has limited range compared to an absolute barometer. The reading from a sea level corrected barometer will match the weather forecast, but you also need to know your elevation to correctly use the information.

Can I call the to check barometer calibration?

Yes, but you should use the same airport all the time. That way if there is a difference in elevation between your location and the airport that offset will remain constant. Be sure to ask for Station Pressure, which is the same as absolute.

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Drag Racing Prediction (CliMax 3, PCM and Merlin Software)

How does your system handle alcohol cars?

Altalab's prediction programs are designed to predict lean, rich and alcohol vehicles through the use of our Performance Factortm. You can use the PFtm to tweak the predictions to match your vehicle, and even predict ET from a single reference run with confidence. If you are using the program to predict more than one vehicle you can set the PFtm for each reference or data base independently.

In addition to the Performance Factortm, Altalab's programs and weatherstations calculate information about moisture in the air which is most critical to alcohol racers. See VP, AH, DP, and Gr.

Doesn't Altalab have a special program for Junior Dragsters?

All of our software can predict a Jr. Dragster. Both CliMax3 for the Sharp 1270 pocket computer and our PC program (PCM2 v.4.0) have several features to help the junior driver or crew chief. Perhaps the most important is the data base ET predictions. Combined with graphing, the data base can handle even the most unusual vehicle characteristics. In addition, Altalab offers a headwinds/tailwinds function to help the junior crew anticipate ET changes caused by winds. The predicted 60' function can help juniors standardize their 60' times.

Merlin Windows software, which comes with the AltaCom II paging weatherstation, can also predict for Juniors.

Can your programs predict more than one vehicle?

Yes. CliMax3 has room for a maximum of 13 cars (5 single runs for ET prediction, 4 ET data bases, and 4 throttlestop data bases). Most racers store data from multiple tracks or events. You can customize each refernce for jetting and traction changes independently. And of course the PCM program can store as much information as your hard drive can spare.

Merlin Windows Software, which comes with the AltaCom II paging weatherstation, allows the racer to create up to 5 separate, simultaneous predictions of ET and/or TS. Each prediction setup can be customized separately.

I like to run the car lean, will your computer still predict it?

Altalab's prediction programs are designed to predict lean, rich and alcohol vehicles through the use of our Performance Factortm. If you choose to run lean, you can use the PFtm to tweak the predictions to match your vehicle, and even predict ET from a single reference run with confidence. Let's look at why you are running lean.

Some racers without a weatherstation like to run lean because their ET doesn't change much and is easier for them to predict. But running lean has its hazards. For example, a big improvement in the air during a race can cause the lean vehicle to slow down instead of pick up, and the driver may not know when this will happen. A slightly rich vehicle is easier and more reliable to predict . If you have a good weatherstation (and of course : -)we can suggest one) you should consider fattening up to take advantage of this.

If you are running lean by accident, as can happen when you go to a new track, Altalab's computer can help you either by suggesting a jetting change or by suggesting a PFtm that will match the predictions to your vehicle's lean condition.

I don't have time to use the CliMax 3 graphing sheets. Are they really necessary?

Graphing your runs is the single best tool a sportsman racer has for managing predictions and jetting. If you are serious about winning, you will at least master and understand the graphing before you give it up. The manual for Altalab's CliMax3 prediction program contains both ET and Throttlestop graphing sheets which you can copy for your log book. If you have a computer at the track you can use our PCM 2 software to automatically generate and overlay graphs.

The way your runs look on the graph will instantly tell you if your vehicle is too lean or rich for current conditions. If so, the graph will help you determine a Performance Factortm so you can get accurate predictions without changing jetting and losing your time trials as references.

The graph will also reveal bogus runs no matter what their cause. A graph of ET or Throttlestop runs will help you create a prediction data base you have confidence in, so you'll be free to concentrate on driving.

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AltaCom II and Weather Telemetry

Do I have to use a PC?

No, both the Alta and AltaCom II function stand alone. However, the PC software allows you to change the time and date, customize settings, make live drag racing predictions, and download logged weather data.

I don't have a serial port, can I use a usb port?

Yes, you will need Merlin 6.0 (free to registered users).

USB to Serial Support - Use a direct/single USB to serial cable, and stay away from multi-port "hubs". Unplug the serial cable to the weather station when changing PC connections, like from serial jack to USB jack. Power down the weather station before connecting the serial cable.

Can I run the weatherstation from a 12 volt supply?

Yes. Included with your Alta and AltaCom II weatherstation are both a 110 adapter and separate 12 volt power cord.

If I get the Alta can I upgrade to paging later on?

Yes, the Alta is fully upgradeable.

Will it hurt the remote to get wet?

No. The worst that can happen is the RH sensor will become saturated and take time to dry out. Turn off the weatherstation if it rains, to prevent the fan from pulling moisture inside. If the RH sensor does get saturated, put the remote inside a dry warm place and let AltaCom II run until the sensor reads normally.

Should I build a roof or sunshade for the remote?

The remote is designed to operate in direct sunlight, and comes with an aluminum shield.

Do you supply mounting hardware for the remote?

We supply a T-shaped mounting mast that fits over a 1" outside diameter pole. The optional wind sensor fits easily on top of this also.

Can I get extra pagers for AltaCom II?

Extra pagers are available at any time.

What if someone else has an AltaCom at the same race? Will it mess up my transmissions?

No, AltaCom II has carrier detect to keep transmissions separate, and your pager will only receive transmissions from your weatherstation, similar to subscribers of paging networks in big cities.

Can I predict more than one car?

Yes, AltaCom II supports live ET and TS transmissions for up to five vehicles.

Is wind speed factored into the live predictions?

No, but wind data is available on the pager so you can make your own adjustments.

How many runs are needed for predictions?

Both ET and TS can be accurately predicted from a single reference run using our Merlin Software for Windows.

Can Merlin predict a Jr. Dragster?

Yes.

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Racers' Guide to Weather Monitoring
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More Winners Use the Altalab Weatherstation