Re: Speedo Recailibration for WJ
Let's just say that I work with radar and drive alot for a living.
I can say that by far, no one's speedometer is perfect, not even close. On average, they are all off to some degree, typically by 2 or 3 miles per hour in either direction. Something as minor as tread wear or inflation can affect the speedometer.
Speedometer errors also tend to exagerate at higher speeds. For example, 2 mph different at 35mph can equal 10mph error at 65 mph.
However, GPS is not 100% accurate either because it does not acount for elevation, only map speed. GPS isn't affected by temerature, tire preasure, tread wear, or gear wear.
With all of this in mind, I have compared GPS to radar, and at speeds of about 150mph, I can honestly say that the radar and GPS speeds were almost identical, which is actually quite impressive.
No, GPS isn't perfect, but on flat land, I would trust it before trusting anyone's speedometer.