Re: Let's do speedo and rear gear math!
[Re: John_Kunkel]
#1902331
08/30/15 10:50 AM
08/30/15 10:50 AM
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Joined: Jan 2005
Posts: 1,609 Pgh, PA
Bull1tt
OP
top fuel
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OP
top fuel
Joined: Jan 2005
Posts: 1,609
Pgh, PA
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i trust the math, not the gps. Problem is, the math only guarantees an accurate odometer not an accurate speedometer. Many speedo errors are in the head itself. GPS factors in new tire size without having to measure diameter and calculate to the original 7.00 X 14 tire, which the 'math' does not do.
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Re: Let's do speedo and rear gear math!
[Re: Bull1tt]
#1902381
08/30/15 12:36 PM
08/30/15 12:36 PM
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Joined: Sep 2007
Posts: 14,889 up yours
Supercuda
About to go away
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About to go away
Joined: Sep 2007
Posts: 14,889
up yours
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i trust the math, not the gps. Problem is, the math only guarantees an accurate odometer not an accurate speedometer. Many speedo errors are in the head itself. GPS factors in new tire size without having to measure diameter and calculate to the original 7.00 X 14 tire, which the 'math' does not do. Not exactly, what the math does not take into account, because it is an unknown, is the EFFECTIVE diameter of the old and new tire. Effective diameter is the actual diameter with the load of the vehicle on it, not the listed diameter specification. And that is why the math is wrong. Problem solving is a [censored] when you don't know how the formula works.
They say there are no such thing as a stupid question. They say there is always the exception that proves the rule. Don't be the exception.
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Re: Let's do speedo and rear gear math!
[Re: lewtot184]
#1902518
08/30/15 04:54 PM
08/30/15 04:54 PM
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Joined: Jan 2003
Posts: 26,538 Rio Linda, CA
John_Kunkel
Too Many Posts
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Too Many Posts
Joined: Jan 2003
Posts: 26,538
Rio Linda, CA
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FWIW, finally got around to checking my original factory reduction unit and it's .80 reduction.
The INTERNET, the MISinformation superhighway
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Re: Let's do speedo and rear gear math!
[Re: John_Kunkel]
#1903631
09/01/15 01:21 AM
09/01/15 01:21 AM
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Joined: Nov 2003
Posts: 36,041 Lincoln Nebraska
RapidRobert
Circle Track
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Circle Track
Joined: Nov 2003
Posts: 36,041
Lincoln Nebraska
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I dont have GPS but I had assumed it was high tech dead on accurate, ain't so ???. What John said I would get the odo correct with the correct pinion then after that if the speedo ain't correct then it would need to come out & go to a speedometer specialty repair shop. I use 5 mile markers in a row on the interstate to check the odo and those portable lit up digital roadside MPH signs the city sets out on occaision to check the speedo
live every 24 hour block of time like it's your last day on earth
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Re: Let's do speedo and rear gear math!
[Re: John_Kunkel]
#1904236
09/01/15 05:18 PM
09/01/15 05:18 PM
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Joined: Apr 2003
Posts: 12,314 Looking for a way out of Middl...
IMGTX
I Live Here
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I Live Here
Joined: Apr 2003
Posts: 12,314
Looking for a way out of Middl...
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When Lacking a GPS I would drive the car on the Interstate from mile marker to mile marker. Needs to be over 25 miles though, the more miles the better the accuracy. I divide the miles traveled on the odometer and the actual miles travel by the mile marker signs to get a percentage. If it is 20 percent too low I get a speedometer gear with 20 percent less teeth to speed it up. That being said, John is right about speedometer heads being off. My method works for calibrating the Odometer with the hopes the speedometer will be right afterwards.
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