Gear Change and Computer Mileage Calculation - JKowners.com : Jeep Wrangler JK Forum
 
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post #1 of 7 Old 09-17-2010, 09:22 AM Thread Starter
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Gear Change and Computer Mileage Calculation

Does changing gear ratios require any change the to computer for calculating mileage properly...(well...as accurately as it can)?

Just swapped out the 3.21's to 4.10s (love em)...but my mileage on the computer has plummeted...with the same tires etc. If anything, I was expecting it to go UP as there is way more power, and I'm driving pretty gently, and not really spinning any more RPM...just using a higher gear for the most part.

So, not sure what's up...

Thoughts?

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post #2 of 7 Old 09-17-2010, 09:34 AM
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Its a calculated MPG.

You will want to get a programmer like a Superchips that you can correct the tire size & ratio with.

Like this:

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post #3 of 7 Old 09-17-2010, 09:42 AM Thread Starter
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I've got a superchips now....and the tires are the same size (upgrade coming soon).

So there IS an option in the superchips to set a different gear ratio?

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post #4 of 7 Old 09-17-2010, 12:17 PM
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Yeah it's in the advanced menu I beleive.

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post #5 of 7 Old 09-17-2010, 01:48 PM Thread Starter
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Quote:
Originally Posted by wsoffroad View Post
Yeah it's in the advanced menu I beleive.
Thanks all....*whew*....found it, adjusted it, and now back to my regular mileage....scared me for a bit. I was thinking something mechanical was binding up (more than the usual that is).

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post #6 of 7 Old 09-18-2010, 10:43 AM
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Gear ratio change is no problem. Speedo reads from ABS I guess. Mine was right on the money going from 3.21 to 4.10's.. tire size change requires adjustment.
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post #7 of 7 Old 09-18-2010, 05:19 PM
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The gear ratio change should not have any impact on the speedo or the mpg "indicated" except that your mileage will go down because the engine is turning a higher rpm for the same speed. The speedo picks up at the wheel and doesn't care what gears are in it. Changing the setting with the Superchip, however, will affect the shift points. The tire size change is what changes the speed indicated and the mpg indicated. My actual calculated mpg from a verified distance and fuel used, went down with the larger tires and the gear change. Both were expected.

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