You went from 671 rpm's to 638 rpm's.

30.10" to a 31.6" tire


30 X 671 = 20130

30 X 638 = 19140

990/ 671 = 1.47 miles off



400 X 671 = 268400

400 X 638 = 255200

13200/ 671 = 19.67 miles off

 

That will make the odometer about 5% slow. Using that correction, you really got about 12.5 mpg, not 11.9.

 

5.2%

so at 60, he will actually be doing 63.1


He you go. I'm really not that smart, I'm just good with tools.
http://www.miata.net/garage/tirecalc.html

 

ok i did the same... i had 245's on it... then changed to 255's... when i had the 245's on there i could go 230 miles on a half a tank... thats 460 a tank ave.
460/24= 19.166mpg (give or take a mpg)

but now with that 255's i have only seen numbers in the 13.9 range is the best i have gotten with them...

the millage use to be good... but now its not... but the tires wouldent make that big of a difrence would they??

note:
the 245's i had on were a highway tire... now the 255's are a mud/snow tire. thus being more agressive tread...

i new the millage would drop when i put the tires on there... but never did i think i would lose 4mpg. just changed the fuel filter last week... figured that might make a diffrence... no diffrence at all...

another note: most of my driving is on the highway at 70 or the interstate at 80... so if that means anything.

 

Found this site looking for info on gas mileage...signed up to add my two cents!

I have a 2006 with the small V6, low miles. Had it for about 3 months now. Just this week, I got a batch of bad gas. As I was pumping it, the pump started bucking like crazy, and I just shut it off, figuring it was about empty or something. Later that day, I go to start my truck, and had to pump the accelerator like crazy to get it to start. Did that twice. My mileage dropped from about 18mpg, to 10 or 12, roughly.

Also noticed I'm due for an oil change. I had a Dakota (hey, it was cheap!), and it also got much worse mileage when it was time for an oil change.

 

well i change my oil in 3000 intervals like your sposed to... but it still got alot worse.

 

Thats really weird that a v-6 would get suchlow mileage. My 5.4L has NEVER gotten under 13.8 and that was towing. Averages 17.67 over the last 3800 miles. Try getting a tune up, and have them inspect EVERYTHING. Not just the old ford preferred customer checklist. There's no reason, if you drive conservatively, you should see that low mileage. That was one of the reasons i got rid of my 6 and went to an eight. At least i KNOW how bad my gas should be, and don't worry about a huge drop like that. Just stays crappy all thetime!

 

Last time I did something like this I got 40+ MPG... But I was a foot away from the travel trailer in front of me with the A/C off doing 55 MPH...

Normally I get 22MPG on the HWY and 16+ in the city. But when I have a busy week at the FD, I typically get 11-12 MPG, as it's floored then brakes for 2 miles as I negotiate through the city to get there...

 

I had in my V6 2001 manual 235 70 16 from the factory and got like 17 in the city......dad changed the tires to Pirellli`s Scorpion STR 265 75 16....

And the mileage went to 11 mpg, since two years. I drive like a granny ans shift under 2000 rpm, no fast take-offs, no racing, and the milage never go better.

And yes, the truck has been maintained properly....heck, it turned 60,000 kilometers yesterday...

So my guess is, MAYBE your tires are causing that poor mileage...

 

Same swap, same results.
I got 18 - 18.5 highway on the oem 255 tires.
I have never seen 18 on the 265 replacement tires. Lost about 1.5 mpg. I'm 17 mostly highway summer, 16-16.5 highway winter.
I believe it is a combo of revs, tire weight, width.
I have tracked nearly every tank for nine years.

As far as acceleration, when I pulled out of the tire store after the swap, I thought the braking brake was engaged.
The seat of my pants meter was indicating I'd lost two cylinders.


Went from stock Wrangler AP 255x70x16 @ 68K
To Michelin LTX M/S 265x70x16 currently 40K.

 

lol but also with bigger tires your gunna put on more miles then your spedo will read... i did a test on my trip last weekend... for about 3 miles it is right on the same number every mile marker... then at about 5 miles it only reads .9 miles instead of the full mile... so you are actually putting on more miles then your pickup is telling you... not a huge difrence but that could account for about .3 of you mpg lose.

 

^^^^^^^^^^

 

Gas grades are controversial. While people complain about "winter gas", "summer gas" is right around the corner for some of us, and then there is "California Re-Formulated Gas". Here in CA, at least according to the broadcast news, "summer gas" is suppose to emit less pollutants, get worst mileage, and subsequently cost the consumer more because we have to pay for more gas to go the same distance. But doesn't "California Re-Formulated Gas" guarantee that we get cleaner gas (crappy gas translating to more detergents + additives and less energy) all year around?

I've seen my tank average rise and fall. It's always a surprise when the next "LOW FUEL" light comes on, and what my MPG computes to. With the ScanGauge II, I've seen daily averages from the low teens, up to the low twenties. We each have too many variables to consider, from gross weight, to driving habits, to driving conditions.

Get rid of your girlfriend and/or wife. The more she weighs, the more gas you save. Not only are you no longer hauling around her big butt, but you save on all those trip distances from all the rides that you are not giving her. See what that will save you in a month. For me: monthly gas - 31 Days(fat *** + pick me up + drive me to) = new car payment. Not to mention the wear & tear she was adding to my old beater's shocks & springs.

KickBoxing - Sport of the Future

 

just pulled a 5 (foot wide) by 10 (foot long) dresson trailer... not inclosed nothing just a normal trailer. with one of those big tail gates on the back... i woulda put it down... but i couldent cause of the side walls we put on the trailer... anyway... i only got 9.3 mpg!!!!! 9.3 mpg for a V6 that is horrible... anyway... i just changed the oil today from 10w 40 to 5w 20 (the recomended stuff) im hoping that i see a millage increase... do you think i will with diffrent oil.?