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Discussion Starter · #1 ·
Help me figure my highway mileage. I took her on a trip today.......all highway to see if the MPG improved from the 10.7 I have been getting around town. I filled up, drove 160.1 miles and refilled with 9.813 gallons. According to my GPS, I was running 63 MPH or 60 MPH on the speedo. How much does that change things? Thanks, Brad
 

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if the miles were per the dic you go miles per dic x 1.078 to get actual miles , actual miles divided by gallons used = mpg,in your case that is 17.6
 

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If you haven't recalibrated the speedo on the truck, you're actually traveling faster than the truck thinks while your tires are turning fewer revs per mile w/ the 285's- So your mileage trip is going to show fewer miles than were actually traveled. To get the most accurate measure, use the mileage trip on your GPS if you have one.

But based on your figures, I’d say you got no worse than 16.3 mpg. Probably more like 17+
 

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if the miles were per the dic you go miles per dic x 1.078 to get actual miles , actual miles divided by gallons used = mpg,in your case that is 17.6
that formula will not work if you have already recalibrated your speedo to adjust for the 285s
 

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Discussion Starter · #5 · (Edited)
if the miles were per the dic you go miles per dic x 1.078 to get actual miles , actual miles divided by gallons used = mpg,in your case that is 17.6


How do you get that formula? I'm trying to learn this stuff on my own, but I'm a little lost on this one. I probably should have checked other speeds, but I only noticed at 60 on the speedo was 63 on the GPS. So, how can I use this to figure any given mileage, if I go 3 miles or 300? Also, I had been running the PPE Economy on 90 HP, but returned it back to stock before the trip, so I assume it returns to stock tire size etc...Thanks, Brad
 

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i got that formula off of one of the tire size calculator websites ,all it does is compensate for the difference between the 245 & the 285,with that taller tire we are actually traveling farther than the dic says on an unreprogrammed speedo. also when your speedo says 60 you are really doing around 64(60x1.078=64.68),use this to adjust your mph or your total miles driven per the dic if you have not reprogrammed speedo to adjust for 285s
your welcome, Bo
 

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check the odometer. Get on a strech of interstate hwy and check the odo by watching the mile post. Go ten miles and see how far off you are. Also you can check your speedo with the milepost method.Set the cruise at 60 mph, go 1 mile and it should take 60 seconds. If it takes less than 1 min to go 1 mile bump the cruise down 1 mph and go another mile. Keep doing this untill you get the magic number. 1mile= 1 [email protected] 60 mph
 

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Can't you leave the stock tune in (like you did) but correct the speedo with the PPE?
 

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Discussion Starter · #9 ·
That's where I'm not sure if it returned everything back to stock, when I hit return to stock, or not. Regardless, my speedo is 3 MPH slower than what I am actually going, according to the GPS.
 
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