Many of the trailer mounted devices actually use recycled old radar guns. They usually don't bother to calibrate them very often or well. Those old guns weren't very sensitive and emitted a lot of power. I remember years ago I had a poor quality detector, driving in rural Nevada. The detector started warning me of X-band. 10 miles!! later I passed the oncoming "county mountie", in an old beat up Ford Bronco, using a very old radar unit in the front window. I had time before seeing the vehicle to remove my detector from the windshield, turn it each way to see the signal disappear and come back, scratch my head, and replace it. I DID make sure I was legal! Pearl reflects the trailer signals pretty well, as on the "Sea to Sky Highway", #99, I get speed displays every time at about 100 metres. -Some- people play with those trailer units, trying to see how big a number they can post, with someone else photographing the results. Not very smart!
Everytime I try and set off one of the radar trailers, it just says SLOW DOWN and flashes 45 at me when I'm doing 55 uphill. I hate that hill because its a cop favorite especially after hte high school gets out and I have to drive up at the same time. I try and pick up speed amd momentum before so the MPG hit isnt as bad because its a good mile uphill but always nervous I'll get it.
My wife can assure you that the Prius shows up all too well on whatever Police radar is used around here, and that with the new 195/60/15 tires, the speedometer is calibrated perfectly.
I think you may have hit it on the head, Tom. My experience has been the same thing. Here in our community, there are many places where they've installed those signs that say "Your Speed" and have an embedded speed radar. About 95% of the time the sign reads my speed (always about 1mph LOWER than what my spedometer reads???) and 5% of the time they don't read at all. My guess: they are aimed a bit higher.
For those who dislike the bother and continuing expense of restocking HARMs for every road trip, there is always the fully legal option of going over the car with a graphite based paint. (Car? What car? )
Oh, I like that idea. The HARMs get expensive, and then there is all that bother with smoke and debris. Tom
Mine does the same thing, it shows about 4 mph slower than what my speedo reads when i go past the stationary radar
I hope the speedo discrepency is not a chronic problem. Mine seems to read consistendly 1mph high wich means I'm clocking miles ever-so-faster than actual distance. For those whose speedo reads low.... you're in luck!
The speedo is not legally allowed to read low, so they're generally set to read high to give some room for calibration error. The odometer is not necessarily set to read high even if the speedo is.
Radar jamming is definitely illegal. Pick up a couple car magazines or search online for radar detectors. I don't know the current models, but a company called Cincinnati Microwave used to make police radar detectors and another company (name?) was competing well against them. There are a few US states where radar detectors are illegal. Some detector units provide means to conceal them inside the car, so that if you do get pulled over, the cop can't see it.
A radar gun is usually under 100 feet away from the target and will receive much more bounced signal then a aircraft radar array which is miles away from the aircraft it's trying to spot. A standard radar gun can still clock a $1 billion stealth bomber taking off if it's in range. If you don't want a ticket don't speed. In states like Washington State they clock you with lasers now and airplanes. If you are really really unlucky you will get an unmarked police car following your for 20 minutes documenting every infraction you do and they they pull you over when you get to about $3000 of infractions and give you your bill. We also have $1000 tickets now for driving in the HOV lane with less then the number of people required. I'm waiting for the traffic cams and automatic ticket systems that they have in Australia where the camera's will issue speeding tickets to ever single driver going over the speed limit. The funny part is that I haven't gone the speed limit in years because traffic rarely goes over 30 mph. I think I even forgot how to drive at speeds like 70 and 75.
I went through one of those speedo check radars on Friday, no reading. I only go through them rarely as we have few of them in Adelaide. There is a fixed speedo check radar on the Western Highway near Melbourne which is the one that didn't pick me up.
