Gas Mileage

hbkid22

hbkid22

Member
I know there are a bunch of threads on gas but I have a 2009 2dr Sport with 35s, 3.5" lift with 3.21 gears and was getting 15mpg. Lately it has been declining pretty rapidly and this last trip was all highway miles and I was getting 11.5mpg. I was driving around 70 and RPMs were around 2100-2500 depending if I was in 5th or 6th.

Questions.

Does tire pressure make a big difference on mpg? Running 30 right now but had it up at 35 at one point.

Will gears help out much?

I also have an issue when filling up gas. At times I can only pull the handle 1/4 otherwise the nozzle will turn off as if gas is full. Could there be an issue with vacuum/pressure in the tank causing issue with mpg? Might be a stretch but curious.
 
cozdude

cozdude

Guy with a Red 2-Door
hbkid22 said:
Does tire pressure make a big difference on mpg? Running 30 right now but had it up at 35 at one point.

Will gears help out much?

I also have an issue when filling up gas. At times I can only pull the handle 1/4 otherwise the nozzle will turn off as if gas is full. Could there be an issue with vacuum/pressure in the tank causing issue with mpg? Might be a stretch but curious.
Click to expand...

Yes it does. a higher PSI will help but it leads to uneven tire wear. if your only doing it for long highway trips then it will be worth it.

Yes they will help a bit.

not sure on this one.
 
JAGS

JAGS

Hooked
cozdude said:
Yes it does. a higher PSI will help but it leads to uneven tire wear. if your only doing it for long highway trips then it will be worth it.

Yes they will help a bit.

not sure on this one.
Click to expand...

In my limited real world test, I'll concur. Running 34-35 psi for about 7k, I could already see uneven wear starting on my newer trail grapplers.

Slowly started to drop PSI and now am at what seems to be the norm of 28. MPG decline was negligible, maybe .5-1.

Certainly not enough to burn through 2k in tires needlessly early. My .02.
 
wayoflife

wayoflife

Administrator
Staff member
hbkid22 said:
I know there are a bunch of threads on gas but I have a 2009 2dr Sport with 35s, 3.5" lift with 3.21 gears and was getting 15mpg. Lately it has been declining pretty rapidly and this last trip was all highway miles and I was getting 11.5mpg. I was driving around 70 and RPMs were around 2100-2500 depending if I was in 5th or 6th.

Questions.

Does tire pressure make a big difference on mpg? Running 30 right now but had it up at 35 at one point.

Will gears help out much?
Click to expand...

Yes, PSI will make a difference but, as mentioned, will cause uneven wear of your tread. What will make even a bigger difference is the type of tread you are running as a mud terrain will have a much greater rolling resistance than an all terrain or even street tread. Also, regearing will help especially if you have an automatic.

I also have an issue when filling up gas. At times I can only pull the handle 1/4 otherwise the nozzle will turn off as if gas is full. Could there be an issue with vacuum/pressure in the tank causing issue with mpg? Might be a stretch but curious.
Click to expand...

Sounds like there is an issue with the venting and that is causing a build up of pressure. This would be unrelated to your MPG.
 
hbkid22

hbkid22

Member
I will try the PSI and see but can't see it making 4 mpg difference. I just don't know why the drop was so big and was curious if anyone has experienced it.

And I have a manual so the shift points are not the issue.

As for the venting wasn't sure if that tied into anything and also wasn't sure what it was called.
 
wayoflife

wayoflife

Administrator
Staff member
hbkid22 said:
I will try the PSI and see but can't see it making 4 mpg difference. I just don't know why the drop was so big and was curious if anyone has experienced it.
Click to expand...

4 MPG is about the difference I saw between running a set of Toyo MT's vs. a set of Falken Wildpeak AT's. Same size only different tread.
 
hbkid22

hbkid22

Member
wayoflife said:
4 MPG is about the difference I saw between running a set of Toyo MT's vs. a set of Falken Wildpeak AT's. Same size only different tread.
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I should clarify that I have not changed a thing on the jeep from when I was getting 14-15mpg to know only getting 11.5 on the last trip. I run BFG ATs now.

I have not purchased my chip yet to recalibrate but again nothing has changed from when I was getting the higher MPG for a couple months.

Sorry for the confusion. As I look back at my original post it did not clarify that.
 
wayoflife

wayoflife

Administrator
Staff member
I thought you said that you changed your PSI? Still, tire wear alone will cause more rolling resistance.
 
hbkid22

hbkid22

Member
wayoflife said:
I thought you said that you changed your PSI? Still, tire wear alone will cause more rolling resistance.
Click to expand...

Actually you are correct. Sorry about that. We just got done driving 800 miles and I have not been to sleep since yesterday morning. Still out of it.
 
hbkid22

hbkid22

Member
So I am a noob. For some reason my pressure was at 21 psi. Don't know how but that is what they were. Went up to 31 right now and was back up to 13.5. Will go up to 34 again for the rest of the trip home.

How often do you check your pressure? I don't have a gauge so I can't tell unless I actually use a gauge.
 
hbkid22

hbkid22

Member
Question. Since I have not reset the speedometer with the new tires I know the MPH will be off but can that also mess up the odometer and throw off the miles you actually get?
 
cozdude

cozdude

Guy with a Red 2-Door
hbkid22 said:
Question. Since I have not reset the speedometer with the new tires I know the MPH will be off but can that also mess up the odometer and throw off the miles you actually get?
Click to expand...

Yes it can because the computer still thinks it's turning a smaller tire
 
cozdude

cozdude

Guy with a Red 2-Door
hbkid22 said:
Ok. That is what I thought so I should retract this thread. I was wondering why the miles were off so bad. Until I reset I can't get a good reading.
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True you can not till you reset. Even after I reset I still don't trust the computer. I still do the old pen and paper way of figuring out my average mpg from time to time. :crazyeyes:
 
hbkid22

hbkid22

Member
cozdude said:
True you can not till you reset. Even after I reset I still don't trust the computer. I still do the old pen and paper way of figuring out my average mpg from time to time. :crazyeyes:
Click to expand...

Oh don't worry I still do that and I have a log in the jeep in case I want to get all crazy.
 
wayoflife

wayoflife

Administrator
Staff member
cozdude said:
True you can not till you reset. Even after I reset I still don't trust the computer. I still do the old pen and paper way of figuring out my average mpg from time to time. :crazyeyes:
Click to expand...

Ummm, pen and paper? :cheesy: Might want to try your iPhone next time, just saying ;) :D
 
Red Knight15

Red Knight15

Caught the Bug
hbkid22 said:
Question. Since I have not reset the speedometer with the new tires I know the MPH will be off but can that also mess up the odometer and throw off the miles you actually get?
Click to expand...

I went from 245/75 to 285/75 and my speedo is off 4 - 5 mph. Checking it with GPS. I've got to get mine recalibrated
 
robx251

robx251

Caught the Bug
I'm running 35" duratrac at 30 psi, with 4" lift with 4.88 gears on my 2010 2dr 6spd. I procaled my tire size I can get 17-18 doing real world driving at 45-55 on back roads here in Maine turning 2300-2500rpm that is an increase of 2mpg from my worn discover stt
 
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