AR7E - Alcester Racing 7's Equipe
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Step Five - Testing and CalibrationWith the car out of gear, roll the car forward until the magnet is just aligned with the sensor. Now, rock the car forward and back a few inches so that the magnet passes the sensor - you should see the head unit burst into life and show some sort of speed reading. If you've got no reading, check your connections and/or take the car for a quick spin (in case you weren't rocking the car back and forth fast enough...) Alternatively, if you have an assistant with a spare magnet, you can leave the car still and get them to repeatedly wave it past the sensor... Eventually you'll get a reading - now it's time to calibrate the system. You will need a tape measure, a few meters of flat ground and an optional piece of chalk. The idea is to measure at least one complete rolling circumference of the tire in situ. Two revolutions is usually enough. Either place a chalk mark on the ground by the tire valve, or place the tape measure starting at this point. Push the car forward in a straight line for at least two revolutions and measure the distance travelled in millimetres. Divide by the number of revolutions - and this is your rolling circumference. But with the BC1200, if you want the unit to read in MPH, you'll need to convert this rolling circumference as follows: Divide the rolling circumference in mm by 1.60934 (or multiply by 0.6214). Round it off to four figures. In our case on 13" CR500s, the actual rolling circ. was 1615mm - to be entered as 1004. And that's it! At AR7E, we have checked these units against GPS speedometers - and they are extremely accurate - even at high speeds. Now we just have to work out how to light the little blighters at night... |
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