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2 hours ago, Mopar1973Man said:

Optimal final ratio should be 3.55 to 3.73. 

 

Example stock mine came with 265/75 R16 tires and 3.55 gears (31.6 inches). Now drop to a 245/75 R16 tire (30.5 inches) not changes the final ratio to 3.69:1 which I'm currently running. When figuring it out you need to start from the stock design typically 265/75 R16 tires.

Ive been reading through a few of your older posts that cover this issue. I found another more “in-depth calculator” where I was able to put in the 47re gears and see what rpm Is at what speed. http://Www.grimmjeeper.com/gears.html

So I’m looking at Falken A/T3W 285/70r17 which are exactly 33” in diameter. With 3.73 gears the final ratio is 2.57. 70mph = 1834 rpm. Does that sound about right? What is the ideal cruising rpm for long haul gas mileage?

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I agree that is the best way to measure.  I don't know what size lift you got but I am 36" front and 36.5" back and I'm about 12" front and 10" back.  So just going by that I would guess that you are

This is the stock 2500 rear blocks, 02 any way. Dont remember the height of the block but can measure later if need be.

It's been a while since I've had them but I measured before and I think I remember measuring a hair over 4 inches...maybe 4.25ish?  

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10 minutes ago, BennyGGG said:

So I’m looking at Falken A/T3W 285/70r17 which are exactly 33” in diameter. With 3.73 gears the final ratio is 2.57. 70mph = 1834 rpm. Does that sound about right?

 

 

Do you mean 3.57:1 ratio final?

 

3.69:1 final like myself I'm at 66 MPH is perfect 2,000 RPM and at 80 MPH is 2,450 RPM's I've documented several runs at 82 MPH still getting 21 MPG. Remember for every 1 pound of rotational weight you drop is like dropping 8 pounds off the frame. Consider the weight of the wheels and tires too. 

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2 minutes ago, Mopar1973Man said:

 

 

Do you mean 3.57:1 ratio final?

 

3.69:1 final like myself I'm at 66 MPH is perfect 2,000 RPM and at 80 MPH is 2,450 RPM's I've documented several runs at 82 MPH still getting 21 MPG. Remember for every 1 pound of rotational weight you drop is like dropping 8 pounds off the frame. Consider the weight of the wheels and tires too. 

Yes. According to this site 3.57:1 final ratio. If I go 4.10 ill be at 2.83 final ratio. 70mph at 2016rpm 

 

now that I’m looking at it I don’t think tire size is included in the final drive ratio Calculator 

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