TJ Gearing types?

[Fishtaco]

I have seen a lot mentioned about factory gearing especially in the tire/wheel upgrade discussions but to tell you the truth I dont really understand the numbers as I have never taken any notice of diff gearing, all I know is its better to have Dana 44,s, I need to go look what I have on my 06, I know it has a 44 rear but have no idea of the gear ratio's.
Why were different gear ratio's used in different years/ models, was it due to gearboxes/transmissions used?
My TJ is totally stock but if I ever decide on lift and bigger tires or buy another already modded looks like its something I would need to know.

Cheers.

 

[Jerry Bransford]

I have seen a lot mentioned about factory gearing especially in the tire/wheel upgrade discussions but to tell you the truth I dont really understand the numbers as I have never taken any notice of diff gearing, all I know is its better to have Dana 44,s, I need to go look what I have on my 06, I know it has a 44 rear but have no idea of the gear ratio's.
Why were different gear ratio's used in different years/ models, was it due to gearboxes/transmissions used?
My TJ is totally stock but if I ever decide on lift and bigger tires or buy another already modded looks like its something I would need to know.

Cheers.

Different axle gear ratios are used to compensate for engine sizes, transmission types, and tire sizes. Jeep used 3.07, 3.55, 3.73, 4.10, and 4.56 depending on all that, with a couple of them based on model year. With your Dana 44 on a non-Rubicon, your axles have a 3.73/3.74 ratio installed into your rear axles... the front and rear ratios are .01 apart on all non-Rubicons.

 

[Fishtaco]

Different axle gear ratios are used to compensate for engine sizes, transmission types, and tire sizes. Jeep used 3.07, 3.55, 3.73, 4.10, and 4.56 depending on all that, with a couple of them based on model year. With your Dana 44 on a non-Rubicon, your axles have a 3.73/3.74 ratio installed into your rear axles... the front and rear ratios are .01 apart on all non-Rubicons.

So for bigger tires I would ideally need a lower diff gearing of at least 4.10 or could a manual 4.0 handle say 33,s with the
3.73/3.74.
Also the front gearing has to be the same as the rear?

 

[Jerry Bransford]

So for bigger tires I would ideally need a lower diff gearing of at least 4.10 or could a manual 4.0 handle say 33,s with the
3.73/3.74.
Also the front gearing has to be the same as the rear?

With your 6-speed, you could get away with 4.10 on flat terrain. If you have many hills/mountains/grades you drive up much I'd go with 4.56.

Yes the front/rear axles have to be running the same ratio... with 4.10/4.11 and 4.55/4.56 being considered the same ratios since they do vary by .01 front to rear. You just can't mix 3.73 and 4.10, at least if you ever want to shift into 4Hi or 4Lo.

 

[UKTJ]

Different axle gear ratios are used to compensate for engine sizes, transmission types, and tire sizes. Jeep used 3.07, 3.55, 3.73, 4.10, and 4.56 depending on all that, with a couple of them based on model year. With your Dana 44 on a non-Rubicon, your axles have a 3.73/3.74 ratio installed into your rear axles... the front and rear ratios are .01 apart on all non-Rubicons.

I don't think that is always true for export models. I have a UK (RHD) 4.0 manual 2002, Dana 30 front / Dana 44 rear, with 3.07.

 

[Fishtaco]

I don't think that is always true for export models. I have a UK (RHD) 4.0 manual 2002, Dana 30 front / Dana 44 rear, with 3.07.

Just re visiting my Build sheet and yes I too have 3.07 gears with the dana44 rear on my 06.
just as well it has stock wheels and almost stock tires on!
If most exports came with 3.07 gears there's a lot in Australia who swap to 33,s as soon as they buy one.

 

[Fishtaco]

So running 31,s with 3.07 would be like running 33,s with 3.73?

 

[HornedToad]

The six speed is the most forgiving of all the manual transmissions with running bigger tires due to its uniquely low 1st gear and the fact that it has 6 gears overall vs 5. This makes it easy to run bigger tires without regearing by simply ceasing to use 6th on the highway. I’ve run 33s with mine for some time and the only good reason to regear that I see is to get it lower for off-roading purposes.

 

[pc1p]

So running 31,s with 3.07 would be like running 33,s with 3.73?

Mathematically, it would be like 33"s with 3.27 gears - the closest would be 33"s and 3.55's (all of which suck donkey d*$%)

 

[HornedToad]

Also I know there are several vehicle speed calculators out there but this one is my favorite:

https://www.marlincrawler.com/java/getspd_calc.html
A good rule of thumb established by other members here is 3000 rpms at 75mph in your highest gear should be the end goal with regearing

 

[Fishtaco]

Why would the export Dana 44,s have 3,07 gears?

 

[sierradmax]

To some degree. While the math equates to diameter equivalent, other factors need to be considered. Such as rolling mass. I will say though, if you're considering going from 3.07 to 3.73, you might be the first person to ever do so.

 

[Fishtaco]

To some degree. While the math equates to diameter equivalent, other factors need to be considered. Such as rolling mass. I will say though, if you're considering going from 3.07 to 3.73, you might be the first person to ever do so.

Not considering changing any gears lol, I just needed an understanding of the gears!
So my 3.07 gears are totally shit for off road? and if so why would the factory even bother adding a dana 44 with 3.07 gears?

 

[pc1p]

Not considering changing any gears lol, I just needed an understanding of the gears!
So my 3.07 gears are totally shit for off road? and if so why would the factory even bother adding a dana 44 with 3.07 gears?

For many years (at least in the US), vehicle emissions were all theoretical, based on simple EPA calculators that utilized engine RPM as a major contributor. It is possible that the same was done for the AU market as well.

 

[Fishtaco]

Mathematically, it would be like 33"s with 3.27 gears - the closest would be 33"s and 3.55's (all of which suck donkey d*$%)

So 31,s are no good on 3.07 gearing?

 

[Fishtaco]

For many years (at least in the US), vehicle emissions were all theoretical, based on simple EPA calculators that utilized engine RPM as a major contributor. It is possible that the same was done for the AU market as well.

Maybe this is why I have never needed to go over 2500 RPM on any gear change?