Quote:
Originally Posted by Porsche
I always calibrate my speedometer with new wheels and tires by heading out onto the Interstate with my stopwatch.
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Quote:
Originally Posted by Freetime
Or skip all the calculations and put a cellphone with a GPS speedometer in your car and test it. I'm stock and I tested mine the first day I got it. 80mph on the dash and on the phone. Spot on.
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I do a combination of both:
- Calibrate with multiple radar speed sensors (to verify general accuracy of radar vs vehicle speed). I ran across about 10 of these from my CA > WY > CA drive a month ago, and all of them were consistently accurate to what my actual vehicle speed was
- Verify actual vehicle speed with GPS app. I use "GPS Status" which gives me very accurate speed readings as well as location/pitch/roll/acceleration/heading/orientation info
The factory speedometer on my car is dead-on for speed estimation purposes. Will re-verify once my new wheels are on.
As for OP: not sure what the laws are in Quebec, but there's ways of fighting traffic tickets in California that increase your chances of winning.
-alex