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Old 02-17-2014, 02:26 PM
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figuring out MPG

just wondering how you guys are figuring out the MPG with larger tires/different gears?

i've just been taking the miles traveled (on my trip meter) and dividing that by the gallons it takes to fill up. should i be doing something else to factor in the tires/gears?

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Old 02-17-2014, 02:50 PM   #2
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Is your speedo correct? If not find out how much it's off and add or subtract that many miles when you fill up

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Old 02-17-2014, 02:56 PM   #3
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Yeah, all depends if you've changed the speedo gear out..

If its still original you'll just have to figure out how much its off. For example my Jeep came with a 34 tooth and 3.73 gears so when I switched to 33s my speedo was off by 10% until I changed out the speedo gear. I had to add 10% more miles into the equation before dividing the miles by the gallons..
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Old 02-18-2014, 12:28 AM
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well, the previous owner installed a TeraFlex super short sye. it uses a tone ring & sensor. so i can't change anything there. IIRC, when i was emailing TeraFlex about a faulty sensor (a problem i had in the past) he was saying that the ECM would have to be reprogrammed in order to have it calibrated correctly.
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Old 02-18-2014, 09:06 AM
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hmm, anyone have any experience with that part? looks like there was a link in there, but it says it was not found.
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Old 02-18-2014, 10:34 AM   #7
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Link works for me, from my pc, my phone, and two different IP's...?
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Old 02-18-2014, 10:39 AM
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that link works. but there is a link within that one that is supposed to give other reviews on it that doesn't work.
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Old 02-19-2014, 05:35 PM   #9
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Take a handheld GPS. Drive the Jeep 50 mph for example. Read the GPS.

If it says 57 then here is the equation to use to figure mileage:

57/50=1.14

If your odo reads 150 miles when you fill up multiply by 1.14. 150 x 1.14 = 171

You can use the formula with any speed besides 50 and any mileage besides 150.

Simple math.
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Old 02-19-2014, 06:00 PM   #10
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Or you can fill this calculator out. 1 side put all the stock stuff, and in the other put your new gear ratios and tire sizes and you can see the different highway speeds listed in individual gears and rpms, so let's say your speedo says your running 70 at 2500 rpm but on the non stock side of the calculator it says your running 79 at 2500 rpm in the same gear. You can use that info to figure out a formula for your mpg. Using a base 100 measurement is a little easier, so look for the difference at say 50 mph. Double the difference between the 2 speeds, say 50 stock and 56 nonstock. You would then know your driving 112 miles when the odometer says 100. So that's a 12% increase in odometer and speedo readings.

http://www.grimmjeeper.com/gears.html
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Old 02-21-2014, 05:35 PM   #11
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Quote:
Originally Posted by Junky_One View Post
Or you can fill this calculator out. 1 side put all the stock stuff, and in the other put your new gear ratios and tire sizes and you can see the different highway speeds listed in individual gears and rpms, so let's say your speedo says your running 70 at 2500 rpm but on the non stock side of the calculator it says your running 79 at 2500 rpm in the same gear. You can use that info to figure out a formula for your mpg. Using a base 100 measurement is a little easier, so look for the difference at say 50 mph. Double the difference between the 2 speeds, say 50 stock and 56 nonstock. You would then know your driving 112 miles when the odometer says 100. So that's a 12% increase in odometer and speedo readings.

Gear Ratio Calculator
Ya what he said
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Old 02-21-2014, 05:47 PM   #12
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When I was running 3.73's and 33's I just used geographical locations with my phone on a road trip divided by gallons used on fill ups.
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Old 02-21-2014, 05:51 PM   #13
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Quote:
Originally Posted by Ebxgsxr View Post
hmm, anyone have any experience with that part? looks like there was a link in there, but it says it was not found.
I have one on my Jeep...greatest thing since sliced bread. Easily adjustable to whatever tires/gears you have, and plug and play.

Blue Monkey Motorsports, Inc. : : : : HealTech Electronics SpeedoHealer (R): Product Overview

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