# radar speed signs



## sobeit (Nov 11, 2007)

passed on of those speed signs today in a construction zone. it showed me doing 41 mph, my speedometer say 45. Now I wonder which was wrong. Maybe that is why I am getting passed all the time.:grin:


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## Confounded Also (Aug 19, 2015)

I have an easy way I use to check mine.

On a flat, straight stretch of road that has posted mile markers:

> Set Cruise Control for 60MPH
> Watch Odometer; set Trip Odometer if equipped.
> Using stopwatch or clock, time as you pass each mile marker while noting the odometer.

Maintain for 5 miles or more.

The minutes should equal the miles nearly exactly. 10 miles traveled, 10 minutes. Odometer should match mile posts.

It's not as good as a dynamometer, but it will give you a good idea if you need to have something checked by a mechanic.


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## Corday (Mar 3, 2010)

Above info is good. All speedos are a bit off + or -. Changing a gear ratio or tire diameter also requires recalibrating. In the U.S. (except VA), I consider a Radar Detector standard equipment.


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## Midnight Tech (Dec 31, 2001)

I use an app on my phone as my speedometer - mine read about 5 mph off at 65 when it worked.


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