Kestrel 4250 Racing Weather Tracker
5-Year Warranty on all Kestrels

Kestrel 4250 Racing Weather Tracker

Product code: K4250 - 0842R

£0.00 inc. VAT

This product has now been superseded by the Kestrel 5100, which is available here »

The Kestrel 4250 Racing Weather Tracker has been designed for those on the motor racing track, providing a portable weather monitoring station.

The Kestrel 4250 enables racers and pit crews to instantly assess the environmental conditions on the track and to tune their machines accordingly.

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The Kestrel 4250 gives critical measurements of air density, relative air density (RAD), station pressure, moisture content (humidity ratio) and density altitude to racers. With this accurate weather data, racers are able to make those last minute dial-in or tuning decisions.

The atmospheric pressure, temperature and humidity all affect the density of the air. On a hot day, at high altitude or on a moist day, the air is less dense. A reduction in air density reduces the amount of oxygen available for combustion and therefore reduces the engine horsepower and torque possible. For tweaking the fuel/air mixture, the air density is the most important consideration.

Kestrel 4250 measures
  • Wind speed
  • Temperature
  • Relative Humidity
  • Moisture content / humidity ratio / water grains
  • Dew Point
  • Station pressure
  • Barometric pressure
  • Air density
  • Relative air density (RAD)
  • Density altitude
  • Wind Chill
  • Heat index
  • Wet bulb temperature
  • Altitude
  • Time & Date
Choice of measurement units
  • kt, m/s, km/h, mph, ft/min, Beaufort
  • °C, °F
  • %
  • mbar, inHg, hPa, psi
  • m, ft
  • kg/m3, lb/ft3
  • g/kg, gpp
  • Speed ±3% of reading or ±0.1m/s
  • Temperature ±1°C
  • Relative humidity ±3%
  • Dew point ±2°C
  • Pressure ±1.5mbar
  • Density altitude ±75m
  • Air density ±2%
  • Moisture content (water grains) ±10%
  • Altitude ±15m
Operational Range
  • Speed 0.6 to 60 m/s
  • Temperature -45 to +125°C
  • Relative humidity 0 to 100%
  • Pressure 10 to 1100mbar
Specification Range
  • Speed 0.6 to 40 m/s
  • Temperature -29 to +70°C
  • Relative humidity 5 to 95%
  • Pressure 750 to 1100mbar
Available options
Kestrel 4250 features
What makes a Kestrel Unique?
  • Multifunction instrument
  • Graphical displays
  • Data capture up to 3600 readings
  • Minimum/maximum/average values
  • User defined screens
  • Language selection
  • Small robust design
  • High accuracy
  • High precision axle and low-friction Zytel bearings
  • Fast response temperature sensor
  • User replaceable impeller
  • Easy to read back-lit display
  • Hard cover protects impeller
  • Runs from 2 AAA batteries
  • Data upload (with optional PC interface or integrated Bluetooth wireless technology)
  • Available in safety orange
  • 5 year warranty
Typical applications
  • Motor racing weather monitoring for race car tune-up
  • Jet engine tuning
  • Drag racing
Primary Measurement Units Resolution Accuracy
(if less)
Wind Speed
or Air Velocity
m/s 0.1 Larger of 3% of reading, least significant digit or 20 ft/min 0.6 to 60.0 m/s
0.6 to 40.0 m/s
1 inch diameter impeller with precision axle and low-friction Zytel® bearings.
Start-up speed stated as lower limit, readings may be taken down to 0.4 m/s | 79 ft/min | 1.5 km/h | .9 mph | .8 kt after impeller start-up.
Off-axis accuracy -1% @ 5° off-axis; -2% @ 10°; -3% @ 15°.
Calibration drift < 1% after 100 hours use at 16 MPH | 7 m/s.
Replacement impeller (NK PN-0801) field installs without tools (US Patent 5,783,753).
ft/min 1 18 to 11,811 ft/min
118 to 7,874 ft/min
km/h 0.1 2.2 to 216.0 km/h
2.2 to 144.0 km/h
mph 0.1 1.3 to 134.2 mph
1.3 to 89.5 mph
knots 0.1 1.2 to 116.6 knots
1.2 to 77.8 knots
Beaufort 1 0 to 12 B
Temperature °F 0.1 1.8 °F -49.0 to 257.0
-20.0 to 158.0
Air, water or snow temperature. Hermetically-sealed, precision thermistor mounted externally and thermally isolated (US Patent 5,939,645) for rapid response. Airflow of 2.2 mph | 1 m/s or greater provides fastest response and reduction of insulation effect. Calibration drift negligible.
°C 0.1 1.0 °C -45.0 to 125.0
-29.0 to 70.0
Relative Humidity %RH 0.1 3.0 %RH 0.0 to 100.0%
5.0 to 95.0% non-condensing
Polymer capacitive humidity sensor mounted in thin-walled chamber external to case for rapid, accurate response (US Patent 6,257,074). To achieve stated accuracy, unit must be permitted to equilibrate to external temperature when exposed to large, rapid temperature changes and be kept out of direct sunlight. Calibration drift +/- 2% over 24 months. RH may be recalibrated at factory or in field using Kestrel Humidity Calibration Kit (NK PN-0802).
Pressure inHg 0.01 typical 0.04 inHg
max 0.07 inHg
0.30 to 32.48 inHg Air pressure at the location. Adjustable reference altitude allows display of station pressure or barometric pressure corrected to MSL. Monolithic silicon piezoresistive pressure sensor with second-order temperature correction. Pressure sensor may be recalibrated at factory or in field. Kestrel 2500 and 3500 display continuously updating three-hour barometric pressure trend indicator: rising rapidly, rising, steady, falling, falling rapidly. Kestrel 4000 series displays pressure trend through graphing function.
hPa (mb) 0.1 typical 1.5 hPa
max 2.5 hPa
300.0 to 1100.0 hPa 10.0 to 1100.0 hPa
PSI 0.01 typical 0.02 PSI
max 0.04 PSI
0.14 to 15.95 PSI
Wind Chill °F 0.1 1.8 °F Refer to stated ranges for wind speed and temp. Perceived temperature resulting from combined effect of wind speed and temperature. Calculated based on the NWS Wind Chill Temperature (WCT) Index, revised 2001, with wind speed adjusted by a factor of 1.5 to yield equivalent results to wind speed measured at 10 m above ground. Specification temperature limits established by WCT Tables.
°C 0.1 1.0 °C
Heat Index °F 0.1 3.6 °F Refer to stated ranges for temp. and relative humidity. Perceived temperature resulting from the combined effect of temperature and relative humidity. Calculated based on NWS Heat Index (HI) tables. (Specification temperature limits established by HI tables.)
°C 0.1 2.0 °C
Wet Bulb Temperature (Psychrometric) °F 0.1 3.6 °F Refer to stated ranges for temp., relative humidity and pressure. Temperature indicated by a wet bulb psychrometer under forced aspiration. Calculated from temperature, relative humidity and pressure.
°C 0.1 2.0 °C
Dewpoint °F 0.1 3.6 °F Refer to stated ranges for temp. and relative humidity. Temperature to which the air must be cooled at a constant pressure for water vapour to condense into water. Calculated from temperature and relative humidity.
°C 0.1 2.0 °C
Altitude ft 1 typical 50 ft
max 98 ft
-2,300 to 85,000 ft Height above Mean Sea Level ("MSL"). Temperature compensated pressure (barometric) altimeter requires accurate reference barometric pressure to produce maximum absolute accuracy.
m 1 typical 15 m
max 30 m
-700 to 25,900 m
Density Altitude ft 1 246 Refer to stated ranges for temp., relative humidity and pressure. Air density converted to equivalent sea level elevation at the International Standard Atmosphere. Calculated from temperature, pressure and relative humidity.
m 1 75
Max/Avg Wind
Max and average wind calculation may be started and stopped independently of data logging of other values, along with all other wind-related functions: air velocity, crosswind, headwind/tailwind, wind chill, WBGT, TWL, evaporation rate.
Data Storage & Graphical Display, Min/Max/Avg History Minimum, maximum, average and logged history stored and displayed for every measured value. Large capacity data logger with graphical display. Manual and auto data storage. Min/Max/Avg history may be reset independently. Auto-store interval settable from 2 seconds to 12 hours, overwrite on or off. Logs even when display off except for 2 and 5 second intervals (code version 4.18 and later). Data set capacity = 3600.
Data Upload Requires optional PC interface (USB or RS-232) or Bluetooth enabled model and provided software.
Available Bluetooth®
Data Connect
Adjustable power consumption and radio range from up to 30 ft | 9 meters. Individual unit ID and 4-digit PIN code pre-programmed for easy identification and data security when pairing and transmitting. Employs Bluetooth Serial Port Protocol for data transmission.
Display & Backlight Multifunction, multi-digit monochrome dot-matrix display. Choice of aviation green or visible red (NV models only) electroluminescent backlight. Automatic or manual activation.
Response Time & Display Update All measurements except those based on relative humidity respond accurately within 1 second. Relative humidity and all measurements which include RH in their calculation may require as long as 1 minute to fully equilibrate to a large change in the measurement environment. Display updates every 1 second.
Clock / Calendar Real-time hours:minutes:seconds clock, calendar, automatic leap-year adjustment.
Operational & Storage Temperature Range The operational temperature range of the liquid crystal display and batteries is 14° F to 131° F / -10 °C to 55 °C. Measurements beyond the operational range can be taken by briefly exposing unit to extreme conditions such that the display and batteries remain within the operational range. Storage range -22 °F to 140 °F / -30 °C to 60 °C.
Auto Shutdown User-selectable -- 15 or 60 minutes with no key presses or disabled.
Languages English, French, German, Italian, Spanish.
Certifications CE certified, RoHS and WEEE compliant. Individually tested to NIST-traceable standards (written certificate of tests available at additional charge).
Battery AAA Alkaline, two, included. Average life, 400 hours of use, reduced by backlight or Bluetooth radio transmission use.
Environmental Waterproof (IP67 and NEMA-6). MIL-STD-810F, Transit Shock, Method 516.5 Procedure IV; unit only; impact may damage replaceable impeller.
Size & Weight 5.0 x 1.8 x 1.1 in / 12.7 x 4.5 x 2.8 cm, 3.6 oz / 102 g.
Colour Options Safety Orange

The manufacturer reserves the right to amend the specification and therefore the information in this document may be subject to change

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