how to calibrate a speedometer? - Page 2 - Ranger-Forums - The Ultimate Ford Ranger Resource


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  #26  
Old 03-23-2011
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yeha i figure ill take a look at it count the teeth,a nd see if i can find one with another tooth like say mine has 19 teeth and theni would find a 20 tooth gear, from what i've read a gear with one extra tooth should correct it
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  #27  
Old 03-23-2011
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The speedometer is reading slow due to the larger-than-stock tires. So it needs a smaller driven gear to speed it up.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

(original tire diameter / new diameter) x original gear count = new gear count

Examples assuming that the current gear is 19T:

(25" / 29") x19T = 16.38T --> use a 16T gear
(24" / 29") x 19T = 15.72T --> use a 16T gear

[calculated new gear count rounded up or down to nearest available.]

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

This also matches the observed speedometer error:

(55 MPH / 65 MPH) x 19T = 16.08T --> use a 16T gear

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Obviously, if the original gear is not actually 19T, these calculation would need to be redone using the correct tooth count.

After doing the recalibration, it would be a good idea to borrow a GPS and confirm that it is correct.
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  #28  
Old 03-23-2011
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Mines only 5 off and I have 31s
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  #29  
Old 03-24-2011
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Quote:
Originally Posted by LancerRevo View Post
Mines only 5 off and I have 31s
The tire size that you have on there now is only half of the equation. If you had 29's originally and went to 31's, that would cause a smaller error than the OP going from 25's to 29's.
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  #30  
Old 03-24-2011
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yeah, that's the issue, especially since ford probably didn't expect anybody to put "big" tires on my ranger when they designed it, yeah i read on some explore forum about the speedo gear, and that's were i read that if its slow you need another tooth on the gear, well i'll have to keep reseaching, maybe i'll find some kinda handy chart, and then from there find what vehicle might have it, does any body knows if one from an explorer will fit, since i have the same tire size as my dad's explore and i think that they are the same size ti came with and the exact tire code is P235/75R15
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  #31  
Old 03-24-2011
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The Ranger and Explorer gears are the same, just be sure that you stay with manual gears because they are different from automatics. I showed you how to calculate EXACTLY what you need but you'll have to get the current gear size first. Just pull the VSS out and count the teeth or use the color code - easy.
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