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Tachometer accuracy

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Old Apr 1, 2017 | 10:19 AM
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Tachometer accuracy
I have a 1988 Ford F super duty and the door indicates that I have a 4.63. Or a code 72 if I am correct on the ratio. My tachometer is reading 2500 rpm's at 55 miles Per hour. The tire size is 235 85 16 dually? It is a five speed with overdrive. According to my calculations it should be running about 2100 RPMs. Which one is correct?

any help would be appreciated.
 
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Old Apr 1, 2017 | 10:30 AM
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How accurate is the speedometer?
 
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Old Apr 1, 2017 | 10:45 AM
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Gps right on money
 
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Old Apr 1, 2017 | 11:21 AM
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Actually I just went out and scrape the tag on the axle and it says 5.13. Yikes! No highway driving here.
 
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Old Apr 1, 2017 | 11:58 AM
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I run my '97 F-Superduty down the highway at 70 MPH with the 5:13's..........she screams at me but the ol' 460 ain't scattered yet!!!!
 
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