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Tall tire Speedo MPH vs. MPG??

2K views 11 replies 6 participants last post by  rorybellows 
#1 ·
According to my GPS, my speedo is 4 MPH off. And according to my dash computer I average 14 MPG.

Is it safe to say that my 14 MPG can be corrected by 4 to be 18 MPG??
 
#3 ·
Makes sense, I figured it wouldn't be that easy, or that much with these tires.
 
#4 ·
id say 14-15 mpg's sound aboot right with them tires you gots. i have the calmini 5" and 33x10.5 and get aboot 15 mpg's. once i throw on a front skid plate/ air deflector type deal, i hope itll go up a bit. at least make it a little more aerodynamic than a coke machine
 
#6 ·
Mathematically it's like a ratio. Oem tire is to aftermarket tire size the same as computer mpg is to true mpg. If you had 30" tires from the factory and now have 33" tires, you are making 10% LESS rotations going the same speed. That means you are going 10% faster than your speedo says and getting 10% better mileage than your computer say. So instead of your speedo being off 4mph, it's actually off by however much percentage more your bigger tires are than your oem tires.
 
#10 ·
theoretically, yes. here in the real world, no. maybe if he had some new sooper lite mudders on there. then id say gimme some of dem der tires
 
#7 ·
If you were getting 250miles in a 15.00gal fillup in the stock tires, now with the taller tires with 6% difference, you actually traveled 266miles.
stock tire/speedo. that's 16.67mpg.
corrected distance with taller tires, 17.77mpg
this is not accounting the heavier weight of the tire, so you'll prolly hit just 240miles or less in that 15gals of gas.
which is about 0-.5mpg difference.
 
#9 ·
um no? no one said he was gaining mpg over stock, just that the display (or even a straight mpg calc) is wrong because the distance traveled is wrong.
 
#12 ·
reread it. got it now

you should get a speedo reprogrammer. mines spot on now. but i still get shitty gas mileage
 
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