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Unread 06-14-2013, 08:17 PM   #1
cj7guy
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What gears do I have in my axles?

I assume it is stock, I bought it with ~90k on it.

It seems like my revs are pretty high for 70mph.

Can anyone back-calculate the gear ratios I have in my axles?

speedo.jpg  
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Unread 06-14-2013, 08:19 PM   #2
MrSmiley
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My guess would be 3.73. But im not for certian
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Unread 06-14-2013, 08:24 PM   #3
ronjenx
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Why not jack up one tire, rotate it 2 revolutions while counting drive shaft turns?
That number will be your gear ratio.
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Unread 06-15-2013, 09:17 AM   #4
HappyTrails
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What size tires?
Take a look at this chart: http://www.jeepforum.com/forum/attac...atio-chart.jpg

If you have an 07 with a 6-spd, I figure you have 4.10 gears, according to that chart.
I believe all 07's came with 4.10 gears. Should pull pretty well with only 30" tires.
But do like ronjenx suggested to get a true calculation of your gear ratio.
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Unread 06-15-2013, 09:23 AM   #5
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Email Jeep and ask for the build sheet. If you do it today you should know everything you need to know Monday.
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Unread 06-15-2013, 09:43 AM   #6
HappyTrails
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Quote:
Originally Posted by switters88 View Post
Email Jeep and ask for the build sheet. If you do it today you should know everything you need to know Monday.
That would be too easy! Don't we Jeepers always like to take apart our Jeep to figure out how things work, and to make better what the Jeep engineers designed?
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Unread 06-15-2013, 11:55 AM   #7
Tanimal
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Quote:
Originally Posted by HappyTrails View Post
That would be too easy! Don't we Jeepers always like to take apart our Jeep to figure out how things work, and to make better what the Jeep engineers designed?
Jeep has engineers? I thought it was just a bunch of monkeys throwing pieces together.
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Unread 06-15-2013, 10:16 PM   #8
Rtone1583
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Jeep has engineers? I thought it was just a bunch of monkeys throwing pieces together.
It's all a matter of perspective.
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Unread 06-15-2013, 10:30 PM   #9
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Going to have to know which transmission and tire size to figure it out.
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Unread 06-15-2013, 10:41 PM   #10
cj7guy
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Sorry forgot to include my Jeep is a 6 spd manual. I was in 6th gear when I took the photo. I fail to see how tire size has any impact on the vehicle's speed sensor.
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Unread 06-15-2013, 10:51 PM   #11
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Quote:
Originally Posted by cj7guy View Post
I fail to see how tire size has any impact on the vehicle's speed sensor.
Tire size is part of the equation when trying to determine gear ratio by looking at the speedometer and tachometer.
For example...
If you put bugger tires on your Jeep, the speedometer will read slower for the same physical speed of the Jeep.


It takes only a few minutes to get your answer if you jack a tire and spin it by hand, 2 revolutions.
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Unread 06-15-2013, 11:31 PM   #12
Rtone1583
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Tire size plays a huge part.

For instance, for the indicated numbers provided in your picture, you could be running any one of the following setups and obtain the same numbers.

3.21 gears with 23" tires runs at 2757 RPM's at 70 MPH.

3.73 gears with 27" tires runs at 2729 RPM's at 70 MPH.

4.10 gears with 30" tires runs at 2700 RPM's at 70 MPH.

4.56 gears with 33" tires runs at 2730 RPM's at 70 MPH.

4.88 gears with 35" tires runs at 2755 RPM's at 70 MPH.

One other thing to take into account. If the tires are considerably larger than stock, the speed sensor system needs to be recalibrated for the larger size (can be done by the dealer up to a point or can be done with an AEV ProCal or similar programmer).

With the above numbers in mind, I would say that the speed sensor system needs to be calibrated to your tire size as none of the above tire size/gear ratios makes sense (with the exception of maybe 4.88's with 35's) in the world that Jeeps typically operate in.
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Unread 06-16-2013, 08:49 PM   #13
cj7guy
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Quote:
Originally Posted by Rtone1583 View Post
Tire size plays a huge part.

For instance, for the indicated numbers provided in your picture, you could be running any one of the following setups and obtain the same numbers.

3.21 gears with 23" tires runs at 2757 RPM's at 70 MPH.

3.73 gears with 27" tires runs at 2729 RPM's at 70 MPH.

4.10 gears with 30" tires runs at 2700 RPM's at 70 MPH.

4.56 gears with 33" tires runs at 2730 RPM's at 70 MPH.

4.88 gears with 35" tires runs at 2755 RPM's at 70 MPH.

One other thing to take into account. If the tires are considerably larger than stock, the speed sensor system needs to be recalibrated for the larger size (can be done by the dealer up to a point or can be done with an AEV ProCal or similar programmer).

With the above numbers in mind, I would say that the speed sensor system needs to be calibrated to your tire size as none of the above tire size/gear ratios makes sense (with the exception of maybe 4.88's with 35's) in the world that Jeeps typically operate in.
The stock JK speedo is using GPS to determine my speed?
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Unread 06-16-2013, 10:32 PM   #14
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The 2007 JK and JKU came with a 3.21 ratio with the 6 spd, and 4.10 with the auto. 4.10 was optional with the 6 spd. If it was the Rubicon, it was 4.10 with both standard and auto.
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Unread 06-16-2013, 10:48 PM   #15
cj7guy
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Quote:
Originally Posted by PaXJ View Post
The 2007 JK and JKU came with a 3.21 ratio with the 6 spd, and 4.10 with the auto. 4.10 was optional with the 6 spd. If it was the Rubicon, it was 4.10 with both standard and auto.
4.10 if it had the factory tow package?
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