Got a speeding ticket! RANT!
07-16-2006, 03:42 PM
#46
Not sure about the 944, but on the 924's and 928's the manuals recommend not using the instrument panel tach's for timing, etc. Since they aren't calibrated and have too many connections between the coil and instrument panel, they are for driving (not maintence) only.
A simple test of the speedo is to find a road with mile markers, set your speed at 60 mph then time it for a three or four mile stretch. If it takes less than one minute per mile your speedo is slow by that percentage. If longer, it reads too fast.
Dennis
A simple test of the speedo is to find a road with mile markers, set your speed at 60 mph then time it for a three or four mile stretch. If it takes less than one minute per mile your speedo is slow by that percentage. If longer, it reads too fast.
Dennis
07-16-2006, 05:01 PM
#47
Burning Brakes
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Why was your speed off with the officer's quoted speed?
Several reasons, of which speedo error is a small one:
1) Cosine Error
2) Radar gun calibration/capture error
3) Reaction time
Cosine error can be a big one. If the guy isn't standing directly in front of you, in your line of travel, he'll read a lower speed. At 90° alongside you, he'll read zero MPH no matter how fast you're going. The reading from the side of the road is ALWAYS lower because of the cosine error. At 20°, 100MPH should read as about 93MPH. At 45° it should read as about 70MPH.
Keith
Several reasons, of which speedo error is a small one:
1) Cosine Error
2) Radar gun calibration/capture error
3) Reaction time
Cosine error can be a big one. If the guy isn't standing directly in front of you, in your line of travel, he'll read a lower speed. At 90° alongside you, he'll read zero MPH no matter how fast you're going. The reading from the side of the road is ALWAYS lower because of the cosine error. At 20°, 100MPH should read as about 93MPH. At 45° it should read as about 70MPH.
Keith
