Join Date: Jul 2008
Location: Northwest Central Jersey
Hope my math is right!
I am not good at math at all but I think I have this right. Please let me know where (not if) I made a error. I entered my first fill up into fuelly.com and the calculation is the same as my computer in my Jeep even though I have not adjusted the tire size or anything like that. The CPU and fuelly were at 14.3 How does that work? My mileage is still off but the MPG average is right on. Here is how I came up with the correct number to enter into fuelly so let me know if I am messed up.
Stock tire = 29.5" - 92.63" circumference
New tire = 31.5" - 98.91" circumference
The CPU says I drove 226 miles since last fill up so here is how I came up with the number of revolutions the tire made during that time.
92.63inches = 154,586.6revs
That means that the computer thinks the tire made 154,586.6 revolutions since the last fill up. From there I think I can calculate the actual miles like this:
x 98.91inches<--new tire circumference
12inches/foot = 1,274,180.3feet
5280feet/mile = 241.3miles
This means that I actually went 241.3 miles on my last fill up even though the computer in the jeep says I went 226 miles. The computer also calculated the average MPG to 14.3. so.....
16.892gallons = 14.3MPG
If all of that is correct then how is it that the XK knows the correct MPG but not the correct mileage? or maybe it is just a strange coincidence.
Bright Silver 4.7L 2.25 RR/OME lift, Kumho KL71 265/70/17, Flashpaq, Lights, rack, intake, Super44, mopar skids, 4x belly guard, rear fog lights, MM9500 winch, GetLost4x4 winch mount
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