Speedometer says 70MPH but GPS says 67MPH
#21
Join Date: May 2008
Location: Great Mills, MD
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if you guys want to know how GPS units work in determining the speed at which you are going, let me know. I had to get very deep into this subject when I was in the military (gotta love the advancement tests). I had to learn about the GPS system.
Personally, I would trust the speed of a GPS unit over the factory speedo. Simple things like changing your tire size/width can cause the speedo to read wrong. I at one point had a 16.7% error in my speedo (when it indicated 60 mph, I was actually doing 70). Even straight from the factory, I have seen some cars reading as much as 2% in error. Hence why ever time I get into a new car and I get a chance to calibrate the speedo, I do. That way I know exactly the error in the speedo and can compensate for it.
By the way, telling a cop, "My speedo was only saying 65 MPH, I don't know how you clocked me at 70" does not work. TRUST ME!!!!! That normally only will garantee that you get a ticket along with a fix it ticket.
Personally, I would trust the speed of a GPS unit over the factory speedo. Simple things like changing your tire size/width can cause the speedo to read wrong. I at one point had a 16.7% error in my speedo (when it indicated 60 mph, I was actually doing 70). Even straight from the factory, I have seen some cars reading as much as 2% in error. Hence why ever time I get into a new car and I get a chance to calibrate the speedo, I do. That way I know exactly the error in the speedo and can compensate for it.
By the way, telling a cop, "My speedo was only saying 65 MPH, I don't know how you clocked me at 70" does not work. TRUST ME!!!!! That normally only will garantee that you get a ticket along with a fix it ticket.
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