Quick MPG question
09-25-2015 | 05:58 PM
#1
Thread Starter
JK Enthusiast
Joined: Mar 2015
Posts: 149
Likes: 0
Quick MPG question
Alright so I don't care too much about MPG as my last jeep got 8 mpg and was a DD but my current JK has the 3.8L with 4:10 gearing, I'm upgrading to 35's soon and would like to know what kind of mpg I should expect. Also would it be wise to regear to 4:56's or something different.. I have stock sized duratracs and the jeep is pretty sluggish with those but I can go 85 all day on the highway getting about 15 mpg and then 20 in city according to my trail dash.
09-25-2015 | 06:24 PM
#2
JK Jedi Master
Joined: Jan 2008
Posts: 11,463
Likes: 162
From: Austin <--> Colorado Springs
Yes, going to taller tires will make it more sluggish and will cause the loss of mpg's. Regearing will bring the engine rpm's back up to an appropriate range, and has been known to bring back some of the lost mpg's.
For what ratio is best ... open a few of the thousand previous threads on it. General concensus seems to be 4.88 for a 3.8 manual, or 5.13 for a 3.8 auto. But then you need to take all of the variables into account. 2door or 4door. Actual tire size. Tire and wheel weight. Where you live, altitude or sea level, lots of hills/mountains or absolutely flat. Lots of city with minimal highway, or mostly 80+ on the freeway. Overall build and weight. Personal preference. Whatever else I forgot to mention. (many people like 4.56 for manuals on 35's instead of 4.88s, and many people like 5.38's or even 4.88's for auto's instead of 5.13. Just depends)
A good start would be to search for the 'JK' gearing charts, they are broken down by engine and transmission. Not a definitive guideline that will work for everyone in every situation, but a good place to start...
For what ratio is best ... open a few of the thousand previous threads on it. General concensus seems to be 4.88 for a 3.8 manual, or 5.13 for a 3.8 auto. But then you need to take all of the variables into account. 2door or 4door. Actual tire size. Tire and wheel weight. Where you live, altitude or sea level, lots of hills/mountains or absolutely flat. Lots of city with minimal highway, or mostly 80+ on the freeway. Overall build and weight. Personal preference. Whatever else I forgot to mention. (many people like 4.56 for manuals on 35's instead of 4.88s, and many people like 5.38's or even 4.88's for auto's instead of 5.13. Just depends)
A good start would be to search for the 'JK' gearing charts, they are broken down by engine and transmission. Not a definitive guideline that will work for everyone in every situation, but a good place to start...
Last edited by nthinuf; 09-25-2015 at 06:27 PM.
09-25-2015 | 06:50 PM
#3
JK Enthusiast
Joined: May 2015
Posts: 210
Likes: 2
From: Richmond, MI
I have only had my 2007 for a few months, 4.10 gears and manual trans on 35 KM2's. I have not calculated the gas mileage myself, the computer tells me I get about 17.4 MPG, it doesn't seem to change much on the highway either.
09-25-2015 | 07:03 PM
#4
JK Enthusiast
Joined: Sep 2013
Posts: 161
Likes: 0
From: prairie village ks
2013 2 dr sport with 35" trail grappler, full metal front bumper, full metal rear bumper, full metal tire carrier, winch, full metal flat fenders, added prob another 1,000 pounds of heft to this damn thing.
373 gears, auto trans. I average around 16-16.2 in the day to day actives. Seen 17-18 on the highway as long as it's not super hilly, but I live in Kansas..... So it's flat as a pancake.
373 gears, auto trans. I average around 16-16.2 in the day to day actives. Seen 17-18 on the highway as long as it's not super hilly, but I live in Kansas..... So it's flat as a pancake.