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maxum3300 01-14-2010 05:46 PM

2?'s Which speedo gear and actual gear ratio
 
I'm about to put 315/75-16 BFG MT's on my Rubicon LJ. It still has the stock gears but what is the actual gear ratio in the Rubicon? I've heard 4.10's and 4.11's. Which is it. Also what speedo gear would I need? Quadratec states that for 4.10's and 35's I should use a 33 tooth gear but yet they don't list one. They have a 32 and a 34 but no 33. Does anyone know if this is correct and where I can get one? Thanks.

Moses2564 01-14-2010 06:09 PM

I believe that the Rubi 44's are geared to true 4.10, while the 4 cylinder Jeeps have 4.11's.

Your Rubicon can not use a tooth gear, as it has an electronic speedometer sensor. You can have the speedo sensor flashed at the dealership for the new tire size, or buy an aftermarket "flasher" that allows you to program multiple tire sizes, and plugs in to the OBDII port.

Jerry Bransford 01-14-2010 06:09 PM

Most TJs with that ratio have a combination of 4.10 and 4.11 because they have different axles front and rear. Your Rubicon has matched Dana 44 axles so they are both the same. I forget which it is, 4.10 or 4.11, but it really doesn't matter... treat them as the same ratio when you look up various things that ask for the axle ratio.

Your Rubicon does not have or use a speedometer gear, it has an electronic speedometer pickup and it needs be reprogrammed for different size tires to re-calibrate the speedometer. Your dealer can reprogram it for some larger tire sizes but not all. Or you can use something like a Truespeed speedometer calibrator which is a small external electronic module that is wired into the speedometer wiring out of the transfer case so you can reprogram it via dip switches for different size tires.

There's another electronic speedometer calibrator module floating around for $80 or so but its name escapes me at the moment. It'd be cheaper and it works as well as the Truespeed from what I undersand.

Jerry Bransford 01-14-2010 06:11 PM

Quote:

Originally Posted by Moses2564 (Post 8692012)
4 cylinder Jeeps have 4.11's.

All Jeeps except the Rubicon have a mix of 4.10 and 4.11 at the front and rear axles when they have that ratio. This is because of the different sizes of ring gears inside the front Dana 30 and rear Dana 35c or Dana 44 axles. Just like 3.54 and 3.55, 3.73 and 3.74, and 4.10 and 4.11... there is always that .01 difference between the non-Rubicon Wrangler's front and rear axles.

The Rubicon has matching Dana 44 axles front and rear so its front and rear ratios match exactly. I don't recall if that is 4.10 or 4.11 but for all intents and purposes, it doesn't matter because they are the same ratio in effect.

Maxxram 01-14-2010 07:06 PM

Quote:

Originally Posted by Jerry Bransford (Post 8692017)

There's another electronic speedometer calibrator module floating around for $80 or so but its name escapes me at the moment. It'd be cheaper and it works as well as the Truespeed from what I undersand.

This would be the Dakota Digital SGI-5. I just ordered one for my 06 LJ Rubicon.
I will be installing it this weekend.

maxum3300 01-15-2010 05:52 AM

Thanks for all the info guys. One more question, if I decide to change the gears do I have to reprogram it again for the new gears?

Maxxram 01-15-2010 06:40 AM

With the electronic speedometer calibration devices, if you should change tire size and/or gear ratio's you simply readjust the device to correct the error.


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