I just checked my mileage for the first time hand calculated and am coming up with what seems an unreasonable number could someone check my sanity and tell me what I am doing wrong?

last fill to top , reset odometer , drove , filled tank to top again , put 10 gal in , odometer showed 222.5 miles

222.5 / 10 = 22.25 is this correct? my ohd shows 14-16 instant and 12.6-14.3 average.
MY tires are 33/12.5/16.5 is this throwing everything out or is there more to firuring this?

Thanks for any help

 

Have you adjusted your speedo for those tires , find out what gear ratio is , then once your speedo is right , you need to reflash your computer so it knows about your tires , filling your tank slow to avoid foaming and getting the same level .

 

gears are 3.55's by the option list in the glove box. How would I go about getting the speedo reset and the like. I don't have the money for a Smarty is there a cheaper alternative?

 

I do believe that the dealer can reset your speedo for you. Not sure on cost, but that's an option. You are doing the math right, just need to adjust for the diameter of the tires. Most tire places on line have a size calculator to show the % difference from your stock tire. Just adjust your miles by that % and do the math again. Your MPG would be REALLY good if you are adjusting by the 8% that you are off on your speedo. 222.5*1.08=240.3/10=24.3 MPG. Make sure that you are filling up at the same pump, same speed, fill to the same level etc to get your best calculation.

 

The dealer may be cheaper than the tool to do yourself .
Link .

http://www.ricksontruck.com/speedometer.html
Rickson Truck Wheels and Accessories

 

Your running the exact same truck as mine-----except for the mods.
My tires are LT285 75R 16"
I put my GPS on the dash and it shows at about 62mph I'm actually doing 65 according to the GPS.
I always fill my truck the same way, let it fill till it stops, then wait about 5 to 10 seconds hit it again till it stops. Thats about the only way I know of to get it "close" to the same each fill up.
I'm consistently getting about 20 to 21 mpg by doing the math like you do
I think that tire size I have is about 2% off so I actually need to add about 2% to my fuel mileage.
Close enough for me.

 

I did some checking and refigured after finding the % differences and it looks like I was getting around 19.5. That is good enough for me I'll never check it again just wanted to know where I was at, it sure is a lot better then the 9 I was getting with my 94 2500 gasser. At least that gives me some barganing power with the wife for future upgrades