Stealth A4?: a bizarre observation...(a bit long)
12-11-1998, 10:42 AM
#1
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Stealth A4?: a bizarre observation...(a bit long)
Our local police force, here in grayest Michigan, has one of those mobile radar units (I assume it's radar) that officers can drop off at a location and zap everyone that passes by. The don't use it for enforcement, it's simply got a big speed limit sign on it and a large display that indicates your speed. If you're going over the posted limit, the display flashes your speed in big red numbers. I guess the idea is to build awareness of both the speed limit and the fact that big brother is keeping an eye on you. I suppose if Michigan required a front license plate, this type of unit could be used as photo radar; but to my knowledge, it's only informational (and a bit of a scare for detector users, I'm sure (though I don't use one...). <p>Anyway, I've passed this device six or seven times at various locations in my neighborhood this week, both in our '98.5 A4 1.8tmq and in our '95 Integra GS-R. When I'm in the Acura, as soon as I see the device's display -- which I assume is the moment the device sees me as well -- it reads within a mph or two of my speedo. When I approach the device in the A4 however, the display reads either a speed well below my actual speed according to my speedo (9 mph when I'm showing 45, for example), or doesn't display a reading at all until I'm literally a few yards away. <p>This occurs in both daytime and night, in rain and in dry, whether accelerating towards the device or braking...uh, with the radio on or off...groceries in the trunk or not.... I can't figure it out. I'm wondering if there's some combination of the angle of the front of the car and the height of the device, or the size and position of the radiator, or, I don't know, the pearlized paint (?) on the car that's causing the radar to scatter. Has anyone else noticed this? Any ideas?<p>Mind you, I'm not complaining. If I could prove that I really did have a stealth car, I could save a lot of time on my commute. : )<p>Thanks,<p>Peter
12-11-1998, 11:31 AM
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What do you mean gray?
What do you mean grayest Michigan?<br>The sun is shining today, here in southeast MI. We've seen the sun more this past year than our normal, though.<br>Where are you seeing this radar speed board? I see one sometimes, on Hickory Grove in Bloomfield Hills.<br>Unfortunately, it picks my speed up pretty much dead on. Maybe it's my red A4....they always 'look' like they're going faster. At least to the cops!<br>-C.
12-11-1998, 11:48 AM
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Re: Well, today isn't gray...but just you wait. : )
The device I pass is complements of the Meridian Twp. police department (near Lansing). <p>Hmmmm...maybe it is the paint (pearl). Maybe that's the *real* reason Audi doesn't paint cars that color any more. : )<p>Remembering once hearing that Lansing has fewer sunnier days than Seattle, <br>Peter<p><br>
12-11-1998, 12:41 PM
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Does this make me a geek for knowing why.
A radar detector measures the rate your distance changes in relation to the detector. You have the calculate the angle that you are to the detector. For example, if your heading directly towards the detector then the speed shown should match your spedo. However, if your car happens to be exactly perpendicular to the detector when the gun is fired, no matter how fast your going the reading will be zero because the "rate of change" between you and the detector is zero.<p>Corey
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12-11-1998, 01:04 PM
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Re: Well, I know that...but I get the readings when approaching essentially head-on...
Its the angle. If I could draw it for you it would be alot easier to understand. Draw it yourself. Take a piece of paper and draw a straight line for the road. Next put a dot right next to the road to simulate the radar gun. Now put several dots along your road (line) to represent your car at diffrent positions. Finnally get a ruler and connect the dots. You want to connect the several car positions to the one radar position. See how the line changes angle? There you go! <p>Corey<br>
12-11-1998, 01:29 PM
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OK. I appreciate the explanation, but I don't think that quite answers it...
Despite the location of the radar -- regardless of what street or corner they place it -- I get the same result. AND, more importantly, I get two totally different readings driving by the same radar position following the same path, but in two different cars. <p>I suspect it's some characteristic of the car and not of the radar position, because the results don't vary by position. Only by car. See what I mean? <p>Sorry if I'm not being clear... : )<p>Thanks again,<p>Peter
