4.10 + 35's = better MPG?
12-23-2009 | 11:38 AM
#1
Thread Starter
JK Enthusiast
Joined: Jul 2008
Posts: 134
Likes: 0
From: Calgary, Alberta, Canada, Canada
4.10 + 35's = better MPG?
Hi,
Just wondering if you go with 35's and keep the Rubi 4.10. Will you get better MPG? I know its a dog for the automatics, and that 6th gears is pointless with the manual. But if you had the speedo reprogrammed, would you get better MPG compared to the 32's with 4.10s?
Thanks
LAHAL
Just wondering if you go with 35's and keep the Rubi 4.10. Will you get better MPG? I know its a dog for the automatics, and that 6th gears is pointless with the manual. But if you had the speedo reprogrammed, would you get better MPG compared to the 32's with 4.10s?
Thanks
LAHAL
12-23-2009 | 11:44 AM
#3
JK Freak
Joined: Jul 2009
Posts: 555
Likes: 0
From: Crandon, WI
I have the 3.73's in my Jeep with a manual and 35" tires and 6th gear is fully functional. I may have to downshift when I reach a hill but everything else seems to work fine.
On a side note, the closer you get back to your stock gear ratio with the larger tires the more gas mileage you are going to get. I believe it is called the "drive by wire" system that will automatically lessen the fuel used when at higher RPMs kind of like that fancy displacement on demand thing in the larger motors.
On a side note, the closer you get back to your stock gear ratio with the larger tires the more gas mileage you are going to get. I believe it is called the "drive by wire" system that will automatically lessen the fuel used when at higher RPMs kind of like that fancy displacement on demand thing in the larger motors.
12-23-2009 | 12:36 PM
#6
JK Enthusiast
Joined: Oct 2009
Posts: 306
Likes: 1
From: Cedar City, Utah
Hi,
Just wondering if you go with 35's and keep the Rubi 4.10. Will you get better MPG? I know its a dog for the automatics, and that 6th gears is pointless with the manual. But if you had the speedo reprogrammed, would you get better MPG compared to the 32's with 4.10s?
Thanks
LAHAL
Just wondering if you go with 35's and keep the Rubi 4.10. Will you get better MPG? I know its a dog for the automatics, and that 6th gears is pointless with the manual. But if you had the speedo reprogrammed, would you get better MPG compared to the 32's with 4.10s?
Thanks
LAHAL
Rotational mass, added friction, poor gearing and not enough HP to push it, all add up to a loss.
If your going with 35's. The 5:38's are the way to go..You'll gain some MPG back. More than that your 3.8 will operate in its powerband.
12-23-2009 | 01:01 PM
#7
JK Junkie
Joined: May 2009
Posts: 3,074
Likes: 1
From: Denton, TX
I still average about 17mpg mixed driving with my 35s and 4.10. I have no desire for "speed" on my normal drive. I have done some extended trips where I held 80-85mph in 6th and rolled right along. Didn't track mileage on those however. I would not be happy with 6th gear highway rpms with anything lower than 4.88. No need to run higher cruise rpm with so many gears to be able to use. If i need more pull i shift, just using the 6spd to my advantage..
Trending Topics
12-23-2009 | 01:45 PM
#8
JK Super Freak
Joined: Apr 2007
Posts: 1,866
Likes: 3
From: Eastern Long Island, NY
we've got same specs and similar heavy shit added to JK, I get 11.5 around town, gets up to 13.5 on highway. Someone posted that the JK computer over estimates the milage, so we're probably in 10-12 area - I'd hate it if it weren't a Jeep - Love it...
12-23-2009 | 02:19 PM
#10
JK Junkie
Joined: May 2009
Posts: 3,074
Likes: 1
From: Denton, TX
The main difference is that you live in Vegas at a much lower elevation that me or the OP.
You lose a fair amount of horsepower for each additional 1000 feet elevation above sea level.
If you drove your JK more frequently at elevations over 5k feet above sea level, in the mountains, you would have the same experience as us--stock gears and 35s are quite poor, and gas mileage improves with lower gears.
At our elevation, even with a programmer (Hypertech or Superchips), 6th gear can only be used down hill with no headwind with 35s and stock gears.
You lose a fair amount of horsepower for each additional 1000 feet elevation above sea level.
If you drove your JK more frequently at elevations over 5k feet above sea level, in the mountains, you would have the same experience as us--stock gears and 35s are quite poor, and gas mileage improves with lower gears.
At our elevation, even with a programmer (Hypertech or Superchips), 6th gear can only be used down hill with no headwind with 35s and stock gears.