Gear Ratio vs MPG

TNP1978

TNP1978

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Oct 13, 2020
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Charlotte, NC
I have a 04 X with the NV3550 transmission and NV231 transfer case with 3.73 gears. My current tires are 32X11.5 MT. I'm in the process of installing a suspension lift and will run 33s. I've read very good write-ups showing the appropriate gear ratio for specific tire sizes. From what I have determined, I I should go with a 4.56 for overall good daily performance. My question is if I were to go to 4.88 or 5.13 but remain on a 33" tire, what type of MPGs might I get doing basic driving around town with some combination of city / highway? Is anyone running this setup? II may at some point decide to run 35s and wouldn't want to have to regear twice.
 
How many miles do you drive, if a lot maybe try to run a cheap beater. I do that with a 120 mile round trip commute. If no to much then likely not enough to make a big difference. I get a beater is another expense, I do it for the mpg and avoid winter salt and reduce daily mileage.
 
15mpg give or take. Depends on where and how you drive.
 
Chris said:
My best advice to you is not to even keep track or care. You’re going to get shit MPGs in a TJ even with stock tires and the appropriate gears.

With 35s you’ll be lucky if you get 10 MPG 🤣
Click to expand...

I must be very lucky.
 
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Ha...not many. I just passed 70K miles. I bought it 6 years ago and am averaging about 3000 miles per year or just a bit less. Your jeep looks good. What size lift are you running?
 
Here is the other way to get a close idea of what it would be like with 4.88 gears.

32" x 3.73 = 2785 RPMs @ 70 MPH in 5th gear
33" x 4.88 = 2755 RPM's @ 70 MPH in 4th gear

This will give you an idea what it will be like.

Screenshot (4).png
 
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TNP1978 said:
Ha...not many. I just passed 70K miles. I bought it 6 years ago and am averaging about 3000 miles per year or just a bit less. Your jeep looks good. What size lift are you running?
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4.25 zone on 33x12.5x15. 3 suspension, 1.25 body, and 1 Motor mount
 
Keep in mind that a lower rpm will not necessarily give you better mpg so don't be afraid to gear correctly for those 33's. Personally I'd go for 4.56. Don't go for 4.10, you'll always be having to downshift for even minor grades. My mpg actually went up by just over 2.5 mpg from sub-12 to 14.6 after regearing from 4.88 to 5.38 to get a little higher rpms so the engine wouldn't have to work as hard.
 
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Jerry Bransford said:
Keep in mind that a lower rpm will not necessarily give you better mpg so don't be afraid to gear correctly for those 33's. Personally I'd go for 4.56. Don't go for 4.10, you'll always be having to downshift for even minor grades. My mpg actually went up by just over 2.5 mpg from sub-12 to 14.6 after regearing from 4.88 to 5.38 to get a little higher rpms so the engine wouldn't have to work as hard.
Click to expand...
Yes, I would 4.56 or shorter. What size tires are you running?
 
Jerry Bransford said:
Keep in mind that a lower rpm will not necessarily give you better mpg so don't be afraid to gear correctly for those 33's. Personally I'd go for 4.56. Don't go for 4.10, you'll always be having to downshift for even minor grades. My mpg actually went up by just over 2.5 mpg from sub-12 to 14.6 after regearing from 4.88 to 5.38 to get a little higher rpms so the engine wouldn't have to work as hard.
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So, with an automatic and 33s would you go lower than 4.56 to, say 4.88?
 
voodooridr said:
How much lower, I still want to be able to keep up with the demented zombies on the freeway
I have no serious rock crawling plans, more of a back road exploring rig
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Assuming your automatic is the 4 speed...

33" tire
42rle/32”/4.56=2478rpm @ 75mph
42rle/32”/4.88=2652rpm @ 75mph
42rle/32”/5.13=2788rpm @ 75mph
42rle/32”/5.38=2923rpm @ 75mph
 
jjvw said:
Assuming your automatic is the 4 speed...

33" tire
42rle/32”/4.56=2478rpm @ 75mph
42rle/32”/4.88=2652rpm @ 75mph
42rle/32”/5.13=2788rpm @ 75mph
42rle/32”/5.38=2923rpm @ 75mph
Click to expand...
that explains why I feel like I need to get out and push on every uphill with my 33s and 3.73s
 
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If you keep it at 60 you will get decent MPG for the vehicle. Every MPH after 60 its going to go down hill fast.
 
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voodooridr said:
that explains why I feel like I need to get out and push on every uphill with my 33s and 3.73s
Click to expand...

Does that look about right for where you are now?

33s
42rle/32”/3.73=2027rpm @ 75mph
 
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L J said:
5.13
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X2, nothing less than 4.88 but 5.13 would be my choice if I had your TJ. And that is a highway ratio recommendation, your 70 mph rpms will be perfect... not too high at all.

I run 5.38 with 35's and 4-speed automatic like yours and wish the highway rpms were a tad higher.
 
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