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  #1  
Old 07-28-2008, 08:58 AM
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Speed radar trailers - accurate?

You know those trailers that the police put up to tell you your speed -
anyone know how accuarate they are? I had to pull of my speedo needle this weekend so when I put it back on I went to test it out...said I was 4 mph too high, so I adjusted it and now I am 3? The second time was at dusk, so maybe that has something to do with it? Because I was sure that I compensated for it!

From memory, these things can vary between each other by a few mph

As far as I'm concerned though, 3 mph off isn't too bad so I might just leave it alone

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Old 07-28-2008, 09:12 AM
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I passed a couple this weekend while traveling and they seemed to be spot on. This was verified by both the Tom Tom GPS and my speedo.
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  #3  
Old 07-28-2008, 09:16 AM
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It's as accurate as any other radar gun, "good enough for government work" as they say. Since these tend not to operate in instant-on mode they are quite good.
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Old 07-28-2008, 09:21 AM
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Hmm, well looks like I'll be pulling the intrument cluster once again! But I've done it so many times now that it is a breeze
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  #5  
Old 07-28-2008, 10:46 AM
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Quote:
Originally Posted by awsrock View Post
You know those trailers that the police put up to tell you your speed -
anyone know how accuarate they are? I had to pull of my speedo needle this weekend so when I put it back on I went to test it out...said I was 4 mph too high, so I adjusted it and now I am 3? The second time was at dusk, so maybe that has something to do with it? Because I was sure that I compensated for it!

From memory, these things can vary between each other by a few mph

As far as I'm concerned though, 3 mph off isn't too bad so I might just leave it alone
How fast were you going... 20 or 60 mph?
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  #6  
Old 07-28-2008, 12:27 PM
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I was going 30 and it said 27

Before I adjusted it the first time, another radar said 35 when I was reading 40
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  #7  
Old 07-28-2008, 12:47 PM
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Those two speed discrepencies are nearly the same: .9 and .875. You may simply be dealing with a tire size issue...
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  #8  
Old 07-28-2008, 12:51 PM
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Most of the ones I've come across in Texas are wrong. All my cars have been GPS'd so I know the accuracy of the speedo.
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  #9  
Old 07-28-2008, 01:07 PM
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Quote:
Originally Posted by KarTek View Post
Those two speed discrepencies are nearly the same: .9 and .875. You may simply be dealing with a tire size issue...
Is there a way to adjust your odo/speedometer to correct for it if you put tires of a different size than the ones that were stock?
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  #10  
Old 07-28-2008, 01:22 PM
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There are shops that specialized in recalibrating (re-gearing) speedos for just that purpose. I went to one in St. Louis.

I had also dealt with a shop in Cali that made custom speedo cables with a fitted gearbox when using a non-OEM speedo application. In my case, I had an AutoMeter speedo typically calibrated for the pinion gear in GM trannys to be used in my VW Bug, in which the cable ran off the front wheel. The custom cable worked flawlessly, and the big bad speedo looked cool in the dash as well!
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  #11  
Old 07-28-2008, 02:03 PM
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Well as far as I know the speedo itself is accurate, I just had to remove the needle when servicing my odometer and when I put it back on it was reading incorrectly. I'll just have to pop it off again and fix it..although 3 mph will be hard to determine based on the little slit on the speedo knob.
If I can find someone with GPS, that might help a lot more.
But, maybe I shouldn't bother, because my tires are near bald so new ones may bring it up to only 1 or 2 mph off, which can hardly be agrued with, IMO
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  #12  
Old 07-28-2008, 02:10 PM
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Ok, I am going to borrow a GPS from a friend tomorrow. Hopefully that will settle the score!
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  #13  
Old 07-28-2008, 05:05 PM
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Those trailers seem to be pretty close for keeping you honest...

I've had a GARMIN 12XL and the 76SX...both read within ±1 mph...not bad for a government box on wheels...if only the information you got from those clowns was that accurate...
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  #14  
Old 07-28-2008, 06:59 PM
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The ones around here are usualy pretty good. Their was one recently on Gulf St and it agreed with my speedo and Garmin GPS.
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  #15  
Old 07-28-2008, 08:08 PM
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I don't know if its my speedo or the trap but during the day the trap is dead on with my speedo, at night the trap shows 3mph slow.

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