gears tires and speed questions.
01-29-2014 | 11:34 AM
#1
Thread Starter
JK Newbie
Joined: Jan 2014
Posts: 5
Likes: 0
From: Grove, Ok
gears tires and speed questions.
Looking for some help and ideas..
Bought my first JK over the weekend and don't know much about it. 07 auto with a small lift, tires are 325-70-17 Nitto terra grapplers. they rub very little at full lock.
I guess my question is what gear ratio do I have.... there's no tag on the diffs.. and seems being I have a 180 mile commute too and from work I want to gain the best Mpg's possible.
I plan to purchase a smaller tire, somewhere in the 33''/35'' range, if im not going to be over geared.
Its unknown if the jeep has a performance tune or not. Future plans for the jeep will follow the lines of an exploration rig not rock crawling.
Speedo reads about 6MPH slower than im actually traveling according to my gps.
At 70MPH (GPS) 64 SPEEDO in OD I'm turning 1900/1950 RPM'S and out of OD about 2600RPM'S.
Thanks In advance! Miles
Bought my first JK over the weekend and don't know much about it. 07 auto with a small lift, tires are 325-70-17 Nitto terra grapplers. they rub very little at full lock.
I guess my question is what gear ratio do I have.... there's no tag on the diffs.. and seems being I have a 180 mile commute too and from work I want to gain the best Mpg's possible.
I plan to purchase a smaller tire, somewhere in the 33''/35'' range, if im not going to be over geared.
Its unknown if the jeep has a performance tune or not. Future plans for the jeep will follow the lines of an exploration rig not rock crawling.
Speedo reads about 6MPH slower than im actually traveling according to my gps.
At 70MPH (GPS) 64 SPEEDO in OD I'm turning 1900/1950 RPM'S and out of OD about 2600RPM'S.
Thanks In advance! Miles
Last edited by tiny_tj; 01-29-2014 at 11:51 AM.
01-29-2014 | 11:48 AM
#2
JK Super Freak
Joined: Jan 2011
Posts: 1,531
Likes: 0
From: Cape Cod
You need a programmer or procal the recalibrate your computer to the tire size you have now. Chances are your gear ratio is 4.10 because you have a rubicon. A 285/70/17 (33") or 285/75/17 (34") would be the biggest I would on stock gears. I highly suggest a superchips programmer to gain little bit more power and to recalibrate for you tire size.
01-29-2014 | 12:56 PM
#3
JK Jedi Master
Joined: Feb 2008
Posts: 12,882
Likes: 172
From: Maine
In '07, the automatic would have come with 4.10 gears whether or on it's a Rubicon, and whether or not it had the tow package.
Because you bought it used, a previous owner could have re-geared it.
Jack a front tire off the ground.
Rotate it by hand 2 complete revolutions while you count the drive shaft turns.
If the drive shaft turned a little over 4 turns, you have the original 4.10 gear ratio.
If the drive shaft turned a little over 4¾ turns, you have 4.88 gears.
A little over 5 turns is 5.13 gears.
A little over 5¼ is 5.38 gears.
A chalk mark on the tire and the drive shaft will make counting turns easier.
Because you bought it used, a previous owner could have re-geared it.
Jack a front tire off the ground.
Rotate it by hand 2 complete revolutions while you count the drive shaft turns.
If the drive shaft turned a little over 4 turns, you have the original 4.10 gear ratio.
If the drive shaft turned a little over 4¾ turns, you have 4.88 gears.
A little over 5 turns is 5.13 gears.
A little over 5¼ is 5.38 gears.
A chalk mark on the tire and the drive shaft will make counting turns easier.
01-30-2014 | 07:06 AM
#4
Thread Starter
JK Newbie
Joined: Jan 2014
Posts: 5
Likes: 0
From: Grove, Ok
I have been looking at programmers!! The car fax shows a dealer front and rear diff ""SERVIVE"" in 09 out of state... I will try the tire drive shaft deal before removing the diff cover and trying to count teeth or look for a number on the ring gear. I do know I have at least a 4.10 gear. Thanks for the ideas!!