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Discussion Starter · #1 ·
So I have been home sick all day, which means using google tv to catch up on netflix shows I have missed, and lots of youtube.

I was screwing around on youtube going through my feed, watching jeep vids, when one of the videos I was watching, the guy mentioned how crappy his gas mileage was with the 4.10's gearing.

I included the video at the bottom, but I am curious this guy is little crazy right? now I realize there is a difference in gas mileage, but this guy is talking 6 MPG that is more than the drop I have seen from gearing in other vehicles.

So what type of gearing do you have? and what is your gas mileage? include tire size, lets see how fun this becomes.

REVIEW: 10th Anniversary Jeep Rubicon- BEST Jeep And Off-Road Vehicle EVER? - YouTube
 

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That guy is a little off with his opinions if you ask me. I've changed from 3.73 gears to 4.10 gears on a couple of different vehicles, and most people would be hard pressed to be able to tell a difference. He makes it out to be a dramatic difference, but at highway speed you're only talking about a 150 RPM difference in engine RPM between those two ratios.

As far as gas mileage goes, here is mine:

6.4 Hemi, 4.10 gears, 35" tires, auto trans = 14.6 mpg combined city and highway
 

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Some of the stuff he said was funny.
You can't get 4.10's on all Wrangler's, just Rubi's...and I doubt if if he got 17.5 mpg IN THE CITY and over 25mpg on the highway (at 70-75mph) in a Sahara.

His averages for a new 4 door Rubi on 4.10's is close to the averages people were getting in the MPG thread.

At 60 mph, with the 5 speed auto and 32" wheels, the difference between 3.73's and 4.10's is 200 rpms. At 70 mph, that difference is 225 rpms.
 

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OK here's a question kinda on topic..

If you are increasing your tire size with 4.10 gears to close to what factory tires and 3.21 gears would give you, would your mileage improve over 4.10 gears and factory Rubi tires?

I understand you may use more in the city because of the increased energy needed to move a larger rolling mass, but on the highway in theory should mileage improve?

(Just ordered a new '14 JKUR and am looking for ways to Justify to the wife to upgrade to '35s and 2.5 inch lift soon after arrival... "Honey, the Jeep Rubicon comes from the factory with lower gears so that you CAN install larger tires AND get better mileage...")
 

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Not to argue, just checking to see if my math is accurate:

At "1850" rpm with 3.73/32.8 Kelly Safari treads producing indicated average ~67 mph.....on the right/best kind of easy hiway trip, that gives me close to 22mpg at times....NOT 'average" mpg by any means.

If 4.10 gives 'only' 225 more rpm at 70, sounds innocent enough, yet is in excess of 10% more power strokes per minute....which in a 200 mile trip @ 70 mph gives 2.857 hours x 60 mins= 171.42 mins x both 1850 and 2075 (225 rpm more) = a whole lot more power strokes and thereby more a)wear; b)power; c)fuel consumption.

My calculation suggests that bare "10%" difference accounts for close to 15% difference in fuel consumption.

But maybe I'm wrong.
 

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re: better mileage with 4.89??? I saw an elaborate formula/practical experiment by one of the old time posters here, who demonstrated how & why he got better mileage with his lower gears & larger tires....but at moderate highway speeds, not 'high speed' IIRC.

There's a lot of variables hard to standardize, it's a tough argument to prove whichever the premise may be.

Good luck in figuring it out.
 

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OK here's a question kinda on topic..

If you are increasing your tire size with 4.10 gears to close to what factory tires and 3.21 gears would give you, would your mileage improve over 4.10 gears and factory Rubi tires?

(Just ordered a new '14 JKUR and am looking for ways to Justify to the wife to upgrade to '35s and 2.5 inch lift soon after arrival... "Honey, the Jeep Rubicon comes from the factory with lower gears so that you CAN install larger tires AND get better mileage...")
Yes and no....

Theoretically....yes...because it all works out to a certain final drive ratio. However, you are also talking about added drag from the lift you will add to fit those 35's, and if you have Nitto's, you are talking about heavy wheels. If you run light 35's on 4.10's with the new engine/tranny, I think it is more of you not taking a huge hit to your fuel economy.

Also, 3.21's don't always give the best MPG....it depends on the driving conditions. No wind, driver only, 60 mph, table flat road....3.21's win. But when you starting throwing in head winds and hills, the 3.21's have to downshift, and they lose their advantage.....especially on the heavier 4 doors.
 

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Well my JKU is in shop getting 4.88s and I am running 315/70/17 Duratracs right now on 3.73 do and average of 16.5ish on highway 15ish mod in town. Well check back after I get it back from shop and see what averages are.
 

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OK here's a question kinda on topic..

If you are increasing your tire size with 4.10 gears to close to what factory tires and 3.21 gears would give you, would your mileage improve over 4.10 gears and factory Rubi tires?

I understand you may use more in the city because of the increased energy needed to move a larger rolling mass, but on the highway in theory should mileage improve?

(Just ordered a new '14 JKUR and am looking for ways to Justify to the wife to upgrade to '35s and 2.5 inch lift soon after arrival... "Honey, the Jeep Rubicon comes from the factory with lower gears so that you CAN install larger tires AND get better mileage...")
Just use what ever logic it takes to convince the war department to loosen purse strings for lift and tires/wheels!!!:thumb:
 

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Not to argue, just checking to see if my math is accurate:

At "1850" rpm with 3.73/32.8 Kelly Safari treads producing indicated average ~67 mph.....on the right/best kind of easy hiway trip, that gives me close to 22mpg at times....NOT 'average" mpg by any means.

If 4.10 gives 'only' 225 more rpm at 70, sounds innocent enough, yet is in excess of 10% more power strokes per minute....which in a 200 mile trip @ 70 mph gives 2.857 hours x 60 mins= 171.42 mins x both 1850 and 2075 (225 rpm more) = a whole lot more power strokes and thereby more a)wear; b)power; c)fuel consumption.

My calculation suggests that bare "10%" difference accounts for close to 15% difference in fuel consumption.

But maybe I'm wrong.
Definitely wrong. I'm not an engineer but I have studied some physics. You can't use a simple linear equation to prove something like that. It's just not that simple. Calculations for mechanical advantage and angular momentum would need to be factored in as well as a host of others. Ultimately, it would depend on how well your ratios are matched with the torque and power curves of the engine AND the demands presented by your particular driving conditions - mass, speed, slope, rates of acceleration, etcetera. These tend to vary widely.
 

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Discussion Starter · #14 ·
MOPWR2U === Props on the Hemi!! still not that bad considering!

Look I know no one buys a jeep for the gas mileage so I just want to get that point across, but this guy is a total tool! Love the off-road footage, from other videos.

panthermark === Totally agree those numbers seem inflated.

HAFICON === look forward to seeing the results.

FXnut === Just tell your wife all the cool kids are doing it, and you need a winch, and bumpers, and a snorkel, and so the suspension needs heavy duty coils, you know to "even" everything out. :)
 
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