effective gear ratio
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Elder User
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effective gear ratio
I have seen this on here before but i could not find the formula anywhere. I just put 315-75-16's and have 4:10's. What is my effective ratio now and how far off will my speedo be?
Laughing Gas
Joined: Jan 2010
Posts: 1,055
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From: Surrey, BC, Canada
I believe 37's with 4:10's is factory ratio. I could be wrong it's been a while since I've seen the chart.
Your speedo if I'm correct should be slightly faster than what your going.
Don't worry if I'm wrong 16 people will correct me.
Your speedo if I'm correct should be slightly faster than what your going.
Don't worry if I'm wrong 16 people will correct me.
Fleet Owner
Joined: Jul 2006
Posts: 20,362
Likes: 823
From: Mi'kma'ki
315-75-16 = 34.6 x 12
effective gear ratio = 3.756 (so 3.76:1 rounded up)
a nice gear ratio close to the latter 3.73 option of the super duty's.
it's a great ratio.still plenty of off the line grunt,yet not so harsh on the rpms.
good middle of the road gearing between 3.55 and 4.10's.
im close to this as well and the idi really likes it @ 3.84.1 (achieved via 3.55's and shorter tires.)
fix your speedo/odo here:
HOW TO RECALIBRATE THE SPEEDOMETER ON 92-96 FORD F-SERIES AND BRONCO .: Articles
first look up your tire manufactures website to get their revs per mile.
you'll notice you'll have to pick one of the closest options on the digital display.
it's really easy with the hardest part being running a ground wire from the clip under the clove box to a ground,and that's not exactly what id call difficult.
effective gear ratio = 3.756 (so 3.76:1 rounded up)
a nice gear ratio close to the latter 3.73 option of the super duty's.
it's a great ratio.still plenty of off the line grunt,yet not so harsh on the rpms.
good middle of the road gearing between 3.55 and 4.10's.
im close to this as well and the idi really likes it @ 3.84.1 (achieved via 3.55's and shorter tires.)
fix your speedo/odo here:
HOW TO RECALIBRATE THE SPEEDOMETER ON 92-96 FORD F-SERIES AND BRONCO .: Articles
first look up your tire manufactures website to get their revs per mile.
you'll notice you'll have to pick one of the closest options on the digital display.
it's really easy with the hardest part being running a ground wire from the clip under the clove box to a ground,and that's not exactly what id call difficult.
Fleet Owner
Joined: Jul 2006
Posts: 20,362
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From: Mi'kma'ki
Posting Guru
Joined: Jan 2010
Posts: 1,665
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From: Terre Haute, IN
Something for you 92-94 guys to keep in mind, you're very limited on how many times you can change the speedometer calibrations... i think its 4 or 5 times, then you either need to replace the PSOM or the whole cluster.... 
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Lead Driver
Joined: Apr 2008
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3.14 i guess i was pretty close at guessin around 3.08. thanks for that who woulda known it was that simple
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Fleet Owner
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From: Mi'kma'ki
i think it's 6 times actually.it shows you how many you have left and is in that article too.
"Speedometer will prove out (sweep across dial and back). The English/Metric and revision levels will be displayed. The last number of the display is the dealer mode programming lockout count. This count shows the number of allowable conversion constant changes remaining. When the count is zero (0), no additional changes can be made to this instrument cluster. If a conversion constant change is required, a service instrument cluster must be ordered. Refer to this section for ordering information."
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