During the last two fill-ups my gas milage has gone to pot... I have the V8 4WD, I used to get rougly 16mpg (16.4 usually)... Now I am averaging 14.2mpg !

Now I threw 265/70-17 Revos on a month ago and I could see some loss because they are aggressive and a size larger, but everything was normal. The truck runs fine, I'm driving no more differently that I did before, but I'm losing about 50mi per fill up. Not funny.

For those who recommended the Revos, you're right they are great tires.

ETA: It's got a new good filter w/ only 2k on it, oil change about 2k ago, and 70k on the truck.

I'm using the fill up amount and mi to calculate, not the computer... Which hasn't changed it's usual average reading.

 

So... are the tires stock size or larger?

You might also want to check and see what psi you're running. I was noticing a drop in my mileage (not that significant) and it looks like it was caused by a tire technician screw up in inflating my driver side front and passenger rear to about 38-39 psi while keeping my passenger front and driver rear at 32.

EDIT:
Oops.. despite reading the post twice I still managed to overlook the size larger comment.
My mistake, sorry!

 

No, like I said, they are a size larger... 70's instead of 65's... The PSI is right, so is the balance, and alignment. But, I drove to ATL, in traffic, and around town after the tires were installed, with no real change in MPG. This has just happened in the last two fill ups.

I'm wondering if I need to have the fuel system cleaned or something, though I'm good about pouring in the injector cleaners.

 

Last tank I got 16.33 mpg, mixture of highway and city. I have 265/70-17 Nitto's and OME suspension.

mochoajr

 

Change in fuel additives by the gas company? I know we kalifornians get some funk gas depending on the season so maybe you guys are experiencing the same stuff?

 

I'm still confused by this part of your post. How are you calculating your mileage again?

 

Yeah dude, if you were in some other parts of the country, you'd be switching off of winterized oxygenated fuel right now.

 

After you fill up your tank, take the amount of miles your drove from the last fill up and divide by the # of gallons it took to fill up the tank.

 

If you have larger tires on you will see a wrong MPG. This is why I'm asking him - I can't figure out if he's taking into account the new tire size with how he worded his post.

 

I've been recording all of my mileage for he last 4K miles and I can tell you I noticed a change in my MPG from 18 to about 16 (pre tire recalculation) about last month around this time (3/9). I was assuming that they'd already switched over?

 

We got ethanol now...I have'nt checked mine yet, but lots are bitching about the sudden crappy mileage now...why do we need this corn ÅÅÅÅ now?

 

That has to be it. If you don't add the compensation to the miles used in the calculation you'll seem to be getting terrible mileage. Wish i could remember that formula, but its too late at night...er, in the morning.

 

I was thinking it might be the winter/summer switch too, which is why I was asking.

I mentioned the tire to give all available information. I calculate my mpg based on the method posted by "mochoajr". My confusion comes from the fact that I had the tires on for more than a few fill-ups BEFORE I started getting crummy gas milage. I filled up yesterday and went to a different station, maybe my usual place is dishing out some crummy gas.
Hey, I just wana make sure there isn't something faulty with my truck, ya know. I'm gonna be ticked if it's the ethanol additive.

 

yup i have been getting really bad mileage lately, like half a tank in the blink of an eye. which got me thinking, could the gas companies make gas that intentionally got bad mileage, more bucks for them? because all of our cars have been getting really bad mileage lately

 

When ever we switch of winterized gas mileage goes up by about 2mpg not down, so I doubt thats it.

Did you get a cold weather streak, that can cause at least 2mpg drop? See what happens with this new gas and go from there.

 

Do you have a V6 or V8? I plan on going with the OME suspension and maybe the nitto's

 

I have the V6.

 

I was searching older topics on mpg and noticed this hadn't been answered so I'll throw my method out there. Your tire size is directly proportional to your miles traveled (a larger tire travels more distance in one revolution than a smaller tire) so I take the difference in tire height pecentage and add that to the odometer reading. For example:

You had 265/65R17s which are 30.56" tall. You went to 265/70R17s which are 31.60" tall. 30.56 / 31.60 = 96.7% or 3.3% increase in height (not that much relatively). So if you traveled say 250 miles on one tank of gas, add 3.3% (8 miles) to that mileage, for a grand total adjusted odo reading of 258 miles. Therefore if you filled up on 15 gallons of gas, and didn't correct your odometer, you would see that you got 16.66 mpg. When in reality you got 17.2 mpg. Not a huge diff in this case, but in my case, I swapped from 225s to 31s, and swapped from 4.10s to 4.88s. My odometer is off 14% now, so I really need to calculate each fillup to see a correct reading!!

Whew...long winded explaination. Now perhaps somebody can tell me where I could find the real world mpg of an '05 Extended Cab Prerunner Taco, which is why I was in this forum in the first place? hehehe...

 

Just a quick note because your math is bothering me.

31.6/30.56 = 103.4%
hence a 3.4% increase

doing the math the other way is just saying that stock size is 96.7% the size of the new tire and hence 3.3% smaller. Going the other way the new tire is 3.4% larger of the stock size.

Sorry, just semantics but it was bothering me

 

Well if you REALLY want to delve into sig figs then we can't approximate tire height off of the metric size since those are just approximations anyways. We will have to get the manufacturer's size rating at the tire pressure that it is going to be used at and then find the percentage increase. Not to mention that 3.3% of 250 miles is 8.25 MILES so we'll have to add that in too....or...uhm...we could just say its about 3% LOL :pat: