I think that I figured out my problem! - Ford Powerstroke Diesel Forum
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Old 11-02-2007, 09:10 AM
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I think that I figured out my problem!

I've been trying to get better fuel economy. I've got a 99 F-250 with the 7.3 and 104,xxx. I have installed a superchips programmer, K and N cold air intake, and a 4" exhaust system. I called superchips direct and the had told me that in order to get my best economy, I should run on the performance setting. ( when not towing ). On a trip, I hand calculated 14.4 mpg. I was driving easy under 2,000 r's. This past weekend, I pulled my 621 Ranger on a trip and I got 10.5 mpg. Tow safe setting... Ok, I admit that I was going over 2,000 r's, but give me a break....... the fish were biting. Anyways, just by chance, I stopped into my buddy's tire shop and asked him what size my stock tires were suppost to be on my truck? He told me 265/75/16's and what I currently have is 285/75/16's!!!!!!!!!!!!!!!!!!!!!!!! So, my question is... could this be why I'm not getting very good mpg? If so, how much could I expect to gain by going back to stock? Thanks in advance for your input.
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  #2  
Old 11-02-2007, 09:13 AM
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I draft behind semis....works wonders. Wish I could help..still trying to figure out my settings.
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Old 11-02-2007, 09:14 AM
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Well partly but you also have to factor in that it changes your speed and therefore your odometer will be off also. With 285's your going almost 2 mph faster then what your speedometer reads and your going more miles then your odometer reads. If you have a handheld gps use that to calculate your mileage.
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Old 11-02-2007, 02:44 PM
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I put the 285/75/16's on my 01 last July and lost two mpg city and highway. I still get 15 pulling a 20 foot (3000lb) boat at 75 mph. My PSD is all stock with a 120k miles.
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Old 11-02-2007, 02:51 PM
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i get 20mpg on econo with my dp with 285/75/16's
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Old 11-02-2007, 04:37 PM
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i really dont think that little tire change is gonna effect mpg much at all. rolling resistance and all that jazz, blah. thats why you got a diesel. a lot of people actually get better mileage with the bigger tires on the highway.
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Old 11-02-2007, 05:34 PM
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I guess that I'm expecting too much............?
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Old 11-02-2007, 05:56 PM
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maybe could try a custom tuned chip for improved mpg and more power both towing and empty. are you running 3.73s or 4.11s? also i dont know when you last did, but fuel filters are usually good for a mpg or two if they are due for replacement.
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Old 11-02-2007, 06:01 PM
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I've gotten 18 MPG on the freeway and 14-16 around town.......dunno how though....
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Old 11-03-2007, 12:17 PM
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I've got 3:73 gears........... fuel filter changed two times in past year... synthetic oil.... so, my main question is will tire size make a difference? I have 285's and stock is calling for 265's Thanks
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