What would make a speedometer read incorrectly?

2001 PONTIAC GRAND AM
198,500 MILES
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NKBRASWELL
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I have a pontiac grand am that the speedometer is reading faster than I am going. It's about 2 mph off, under 50, and 5 mph over 50. All other gauges seem to work just fine, and tires are the correct size.
Nov 9, 2011 at 10:49 PM
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ASEMASTER6371
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have you had any transmission work done lately??

there is a speed sensor for the speedometer that may be reading wrong or has the wrong ring for the speedometer.

Roy
Nov 9, 2011 at 11:17 PM
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BILLYBOB
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HAVE YOU PUT OVER SIZED TIRES ON IT?? IF SO THAT WOULD CHANGE IT
Nov 10, 2011 at 12:42 AM
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NKBRASWELL
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No tranny work or over sized tires. I didn't know how long it has been wrong. I got pulled over the other day. The officer said I was going 66, but I had the cruise set at 60. So I downloaded a GPS speed tracking app. It seems to confirms the problem.
Nov 10, 2011 at 10:31 PM