Speedometer gear calculator? - Vintage Mustang Forums
 
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post #1 of 7 (permalink) Old 08-14-2008, 10:08 PM Thread Starter
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Is there an easy way to figure out what speedometer gear I need? I've changed tire size and rear end gearing. I'm running 245/60R15 tires and 3.25 rear gears behind a wide ratio trans. This is on my 69 Mach 1. Thanks.
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post #2 of 7 (permalink) Old 08-14-2008, 10:21 PM
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What is the Outside diameter of your tires?

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post #3 of 7 (permalink) Old 08-14-2008, 11:39 PM
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Here is a good web site that should be able to help you out. Speedo gear calculator

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1967 coupe- Keith Craft 306 street/T5z with Pro 5.0. Arning Drop/ Bilsteins/ cut 720's up front and 4.5 mideyes out back. 13 inch Cobra discs

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post #4 of 7 (permalink) Old 08-14-2008, 11:49 PM
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The NPD catalog has a calculator printed on the same page where they list speedo gears.

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post #5 of 7 (permalink) Old 08-15-2008, 12:18 AM Thread Starter
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post #6 of 7 (permalink) Old 08-16-2008, 01:28 AM Thread Starter
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Looking at the gear chart in CJ Pony, it is showing the same 16 tooth gear for both the 3.00 and the 3.25 unless theres a difference in F70-14 and FR70-14 tires? How can that be? The F70-14 tire is 24.78" tall, I'm running 245/60R15s that are 26.55" tall. I'm assuming with the bigger tires I would need maybe 1 tooth larger gear? I'm not that good with math, I just know my speed is about 15 MPH to fast right now and would like to get right with out buying and swapping a bunch of gears.
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post #7 of 7 (permalink) Old 08-17-2008, 09:56 PM Thread Starter
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