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Before I bought my 2000 F250 4x2 Supercab LB PSD I did some searching trying to find similar pickups and what their respective MPG may be. Found a few posts but nothing was ever consistent. Also found a lot of "Yeah my 02' CC LB 4x4 with 37's gets 25 MPG!!" Seemed like a load of crap. When I bought the pickup it had 285/75/16's on it. They were Maxxis Bighorn M/T in the rear and Toyo Open County A/T's in the front. I do a 50/50 split of highway and city in hilly terrain. I checked the speedometer against a GPS and was always 1mph faster than the speedo. So using a correction factor of 1.02 ( wont waste time explaining how I figure that buts its close and doesn't change much anyway) I was getting between 14.4 and 14.8 over the course of about ten tanks. NOW I have changed the tires to 265/75/16 Open Country HT tires which are smaller and the mpg range has been 15.5-15.8, with the GPS and speedo in sync. So I saw a solid 1 mpg gain by switching to smaller less aggressive tires. I personally like it better, not just for the mpg gain, but I notice it doesn't down shift as much going up hill and seems to drive a little smoother not lugging those 285s which I dont need on a 4x2 highway hauler. Anyway, thought Id share an honest take on some MPG info.
 

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Better MPG with OEM-size rubber is what almost everybody finds.

15 sounds a bit low for a 4x2. My truck (unmodified) got 18. Of course its a stick.

Read the stickies. You might find a nugget that will help.
 

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Better MPG with OEM-size rubber is what almost everybody finds.
Oh, agreed! Picked up another Jetta. Came with a set of snow tires in the oem size...and summer wheels which were wider than stock and 3 inches larger in diameter than stock. Tire circumference was the same, but it decreased my mpg.

On the other side, I put taller tires on my bus to maintain an rpm and gain mph. The result was less mpg.
 

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Before I bought my 2000 F250 4x2 Supercab LB PSD I did some searching trying to find similar pickups and what their respective MPG may be. Found a few posts but nothing was ever consistent. Also found a lot of "Yeah my 02' CC LB 4x4 with 37's gets 25 MPG!!" Seemed like a load of crap. When I bought the pickup it had 285/75/16's on it. They were Maxxis Bighorn M/T in the rear and Toyo Open County A/T's in the front. I do a 50/50 split of highway and city in hilly terrain. I checked the speedometer against a GPS and was always 1mph faster than the speedo. So using a correction factor of 1.02 ( wont waste time explaining how I figure that buts its close and doesn't change much anyway) I was getting between 14.4 and 14.8 over the course of about ten tanks. NOW I have changed the tires to 265/75/16 Open Country HT tires which are smaller and the mpg range has been 15.5-15.8, with the GPS and speedo in sync. So I saw a solid 1 mpg gain by switching to smaller less aggressive tires. I personally like it better, not just for the mpg gain, but I notice it doesn't down shift as much going up hill and seems to drive a little smoother not lugging those 285s which I dont need on a 4x2 highway hauler. Anyway, thought Id share an honest take on some MPG info.
Congrats on the new found MPGs. However some of that mileage was probably already their, you just could not see it because your speedo was off. Your correction factor for your old tires should have been 1.037. I only know this because I run the 285/75R16 on my truck and using a speedo calculator I found my speedo was off 3.7%. So lets see how this changes your out come:

Lets say you drove your truck on your old tires 400 miles. You add in the correction factor you were using 400 x 1.02 = 408 miles. Lets say it took you 28 gal. to fill up. 408 miles / 28 gal = 14.57 mpg.

Lets try the same calculation using the 1.037 factor. We'll use the same odometer reading of 400 miles and the same 28 gal. of fuel. 400 x 1.037 = 414.8 miles. So... 414.8 miles / 28 gal. = 14.81 mpg.

So the difference for this example is 0.24 mpg. I am not trying to be a dick, you got a great increase out of swapping your tires to a stock size. I just feel as you do in the fact many people report crazy MPG #s all the time. Some times high, some times low. Lots of people swap tires and think WOW I just lost 2 MPGs, when in reality they forgot to compensate for the speedo being off.
 

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I think beel could share his methodology. Sounds like he thought it through.

Personally, I never use the rote concept of "tire size" as the actual circumference can be found for a particular tire. Even the same "sized" tire can be different within a nanufacturer's line up.
 

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Reading this makes my 97 look like a much better buy all those years ago... I got 18mpg all day, every day, city, freeway didn't matter. Just a plain jane bone stock XLT SC LB 4x2 auto.
 

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Discussion Starter #7
Better MPG with OEM-size rubber is what almost everybody finds.

15 sounds a bit low for a 4x2. My truck (unmodified) got 18. Of course its a stick.

Read the stickies. You might find a nugget that will help.
Yeah lately it has been around 15.5 mpg mixed. I think some things that may attribute to this is the fact I have the automatic transmission and I live in mountain terrain in Washington. I am constantly going up and down hill all day. I am moving back to Florida this summer, so Im hoping to see a noticeable difference in the flat terrain.
 

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I am moving back to Florida this summer, so Im hoping to see a noticeable difference in the flat terrain.
Better fuel milage may also be attributed to the lower elevation
 

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isnt florida humid?
 

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Warm humid air is lighter than cold, dry air. See your psychrometric charts.

Aero drag is proportional to air density.

Florida, with low-density air and dead-flat terrain should be excellent MPG country.
 
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