Even if you never drive above a few MPH under the limit, you can still get a radar-generated speeding ticket! Why? Because of law enforcement radar unit calibrations.
That's right, the limit is 40 and you are doing 37 MPH, then you are pulled over and issued a ticket for doing 44 MPH. How is this possible?
Simple - the radar gun has not been regulary calibrated. The cop isn't even aware of his device's malfunction and bottom line is you get a ticket and have to spend money and time in court proving your case. I know this happens often enough, especially in towns that have limited resources to spend on regular testing/calibrations.
It happen to me - I was doing 37MPH in a 40 zone and got a (radar) ticket for doing 42! I didn't fight it but that's when I realized I needed a detector pronto. Now, even doing 2 or 3 MPH under the limit. When the detector goes off, I slow down to about 5 under the limit for insurance.
OK, you say my tires are too large and that makes my speed-o read lower than it should but they are a correct size and passing several "your speed is" sites, my speed-o is within 1 mph accuracy.
So someone who NEVER speeds, you STILL need a good performing detector that gives you a few seconds to slow down more for insurance sake.
Of course finding a detector sensitive enough to give you ample warning is another challenge. After several brands that just didn't give me that extra time to brake safely (detecting the radar ahead BEFORE it starts reading my speed), I opted for a "V1" and it gives me ample time to reduce speed safely to insure not getting a ticket because of a uncalibrated radar unit.
Bottom line - a few extra bucks well spent for the needed protection against un-calibrated radar guns.