What gears do I have?
01-28-2018 | 02:47 PM
#1
Thread Starter
JK Newbie
Joined: Jan 2018
Posts: 0
Likes: 0
From: Tulsa, OK
What gears do I have?
I’ve got a 2015 JKU Sport and know from the original window sticker that it came with 3.73 gears. I bought it used and believe it’s got about 4” of suspension lift with 35” tires. I’ve read a lot about why you’d want to upgrade the gears when lifting and going to bigger tires and understand all of that. But it drives great with this setup rather than sluggish like all the info says... so I’m wondering if the previous owner already replaced the gears. How can I tell?
Like I said, I love the way it drives now so don’t have any concerns. But I’d like to add some selective lockers someday and maybe go to 37’s.
Like I said, I love the way it drives now so don’t have any concerns. But I’d like to add some selective lockers someday and maybe go to 37’s.
01-28-2018 | 02:50 PM
#2
JK Jedi Master
Joined: Feb 2008
Posts: 12,882
Likes: 172
From: Maine
Jack one front tire off the ground.
Put a chalk mark on the tire and the drive shaft.
Rotate the tire by hand 2 complete revolutions while counting the drive shaft turns.
The number will be your gear ratio.
A little less than 3¼ turns will be 3.21 gears.
About 3¾ turns will be 3.73 gears.
A little over 4 turns will be 4.10 gears.
About 4½ turns will be 4.56 gears
A little less than 5 turns will be 4.88 gears
Put a chalk mark on the tire and the drive shaft.
Rotate the tire by hand 2 complete revolutions while counting the drive shaft turns.
The number will be your gear ratio.
A little less than 3¼ turns will be 3.21 gears.
About 3¾ turns will be 3.73 gears.
A little over 4 turns will be 4.10 gears.
About 4½ turns will be 4.56 gears
A little less than 5 turns will be 4.88 gears
01-28-2018 | 05:30 PM
#3
Thread Starter
JK Newbie
Joined: Jan 2018
Posts: 0
Likes: 0
From: Tulsa, OK
Jack one front tire off the ground.
Put a chalk mark on the tire and the drive shaft.
Rotate the tire by hand 2 complete revolutions while counting the drive shaft turns.
The number will be your gear ratio.
A little less than 3¼ turns will be 3.21 gears.
About 3¾ turns will be 3.73 gears.
A little over 4 turns will be 4.10 gears.
About 4½ turns will be 4.56 gears
A little less than 5 turns will be 4.88 gears
Put a chalk mark on the tire and the drive shaft.
Rotate the tire by hand 2 complete revolutions while counting the drive shaft turns.
The number will be your gear ratio.
A little less than 3¼ turns will be 3.21 gears.
About 3¾ turns will be 3.73 gears.
A little over 4 turns will be 4.10 gears.
About 4½ turns will be 4.56 gears
A little less than 5 turns will be 4.88 gears
Thank you. Nice & simple... Why 2 revolutions? Everything I’m reading says the gear ratio is the relationship between how many times the drive shaft rotates in correlation to one revolution of the axle/wheel.
01-28-2018 | 05:58 PM
#4
JK Jedi Master
Joined: Feb 2008
Posts: 12,882
Likes: 172
From: Maine
It's because of the action of the spider gears in the differential. The ring gear turns at exactly half the speed of the axle when only one tire is off the ground.
If you lift both wheels it would be one turn, but you have to make sure both wheels turn exactly together. That is a little difficult if you are by yourself.
If you lift both wheels it would be one turn, but you have to make sure both wheels turn exactly together. That is a little difficult if you are by yourself.
Last edited by ronjenx; 01-28-2018 at 06:00 PM.
01-30-2018 | 12:44 AM
#5
Former Member
Joined: Jan 2018
Posts: 134
Likes: 4
From: Nor-East Uni-Stat
@janes1108 Even though the window sticker (if you're lucky enough to have one included within your purchase) does reflect the gear ratio. It's not uncommon to have the previous owner sway the gear themselves (if their good enough to do so) or have the gears change by a professional installer. We've been very fortunate to have special ordered a 2017 wrangler with the 3.73 gear ratio as reflected on our build sheet & built just for us. So unless you have data sheets indicating what has been done to the jeep, or you've run the vin via Jeep's site.. you'll have to perform the technique @ronjenx described above.