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RPM Question

657 views 9 replies 4 participants last post by  AusRotten 
#1 ·
I just bought a '07 JK and not knowing anything about jeeps I found a lot of after market parts on it. My question is about the gearing. It has BF Goodrich All Terrain KO's 315/75R16's with a 3" Terraflex suspension kit. At 65mph, its about 2200rpm in 6th gear. Is that normal or does it look like it was re geared for tire size?
 
#2 ·
34.6 inch tire - in 6th at 70 would be 2300 with 4.10s according to the chart. So unless its a rubi - it seems it was minimally regeared.
 
#3 ·
If you like to work on your Jeep, and you want to know for sure,
do this:

Chock the front tires, fore and aft.
Put the transmission in neutral.
Emergency brake off.
Jack the left rear tire off the ground.
Put a jack stand under the frame, just in case the jack fails (had to add this).
Put an index mark on the aft end of the drive shaft, visible from the left rear wheel.
Put an index mark on the left rear tire at the 6 o'clock position.
Rotate the left rear tire 2 complete revolutions while counting how many times the index mark on the drive shaft passes its original position.
That number will be your axle ratio.
Remove jack stand and lower jack.
Put transmission in gear or Park, apply emergency brake.
Remove chocks.
If you have limited slip, jack up both rear wheels and rotate one revolution, making sure both tires rotate equally.

If the drive shaft rotated almost 3¼ turns, you have 3.21
If the drive shaft rotated almost 3¾ turns, you have 3.73
If the drive shaft rotated a little over 4 turns, you have 4.10
If the drive shaft rotated 4½ turns, you have 4.56
If the drive shaft rotated a little under 5 turns, you have 4.88
If the drive shaft rotated a little over 5 turns, you have 5.13
 
#5 ·
07 could of had the towing package that would of thrown in 4.10s
 
#7 ·
In '07, the ratios available were 3.21, and 4.10.
Automatic would have been 4.10, with or without the tow package.
6 speed would have been 3.21; 4.10 optional without tow package, required with tow package.
Rubicon was 4.10 in any configuration.
 
#6 ·
Thanks I did not know the 7 had that option - in 11 when I bought mine it was 3.21 standard, 3.73 tow pack and 4.10 Rubi and rubi tow pack.
 
#10 ·
Yes I know that, I will do the wheel spinning thing to help determine the ratio. Ya I have no idea if its factory or just added. Thats what sucks about buying something with changes.
 
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