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Unread 08-05-2010, 10:17 AM   #31
Poor Boy
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35" Yoko Geos running at 32psi

5.13 gears

6 speed

15ish city, 18ish hwy.
Quote:
Originally Posted by jstrubberg View Post
Going to a higher gear ratio will likely give you worse mileage, not better.
not true. you need correct gearing.

Quote:
Originally Posted by JeffinWesternWA View Post
Try to shift at about 2K~ rpm's, coast more into stops and smooth slow starts will add 1-2MPG to your number. Keep tires 2-3 lb over rec pressure. I've averaged OVER 20 MPG on first 3K miles of my JK w/ 6 sp/3.73's. Even got 23 mpg on highway on nice cool day at 65 mph level interstate. Keep the tires well inflated, the "junk" ota the Jeep and the idling to a minimum all will help...
i think 2k is way too low of a shift point for this engine.
~i've found that my engine is happiest running between 2500-2750.
~chalk test your tires. you won't be saving any money on gas if you are prematurely crowning or cupping your expensive tires. 2mpg does not equate a pair of $280 tires.
~i will second keeping crap out of your jeep. take out your back seat if you don't need it. if you feel you safely can, leave the spare at home (and the jack with it). it takes 7hp to move 100lbs.

fwiw, i was seeing similiar numbers to jeff when my rubi was still stock.

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Unread 08-05-2010, 10:26 AM   #32
tavic
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I'm running a Stock 2010 Sport 2 Door (With the most recent Jeep Software), 6 spd Manual, Soft Top, 2.72:1 Gears and P225/75R16 Goodyear Wrangler HT Pizza Cutters. I get an average around 18-19 Highway at 75-80 mph, 21-22 at 60-65 mph.
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Unread 08-05-2010, 12:52 PM   #33
tennistom1
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Quote:
Originally Posted by drowe303 View Post
Truck?

But why is that? Is one not supposed to wonder about his/her gas mileage if they are driving a Jeep?
(My second by the way..)
Yah, I'd call it a truck, anything with a heavy-duty frame that you can haul 3/4 ton of bricks in without breaking the axle would qualify as a truck.

Right, you shouldn't wonder about your mpg. First you'll wonder and then you'll worry and then your hair will fall out, don't do it.

If you want good gas mileage in a 4x4 those Subaru Baja's look cute and have a bed in the back but I wouldn't consider them a truck, but they look real utilitarian for running around town in.

What I'm wondering is why do my Jeeps come from the dealer with 42lbs of air? And if I take it in for service, they fill it air it back up to that.
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Unread 08-05-2010, 01:27 PM   #34
jstrubberg
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Quote:
Originally Posted by Poor Boy View Post
not true. you need correct gearing.
Very true. Unless regearing is preventing you dropping out of overdrive, you gas mileage will go down as gear ratio climbs. You can't run at higher RPM's without using more fuel, all else being equal.
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Unread 08-05-2010, 01:30 PM   #35
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Quote:
Originally Posted by tennistom1 View Post
Right, you shouldn't wonder about your mpg. First you'll wonder and then you'll worry and then your hair will fall out, don't do it.
it was beat to death in the TJ forum when i had that. now we have it here. i think the point isn't that "wahhhh! my mileage sucks!" as it is "i love my jeep, how can eek a couple more MPG's out of it?" If they were all the misguided "my prius is greener than your jeep!" tree-hugging ultra-liberals, they wouldn't be in a unleaded powered brick to begin with.
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Unread 08-05-2010, 01:42 PM   #36
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"my prius is greener than your jeep!"
My hubby always says he wants to hemi mod a prius
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Unread 08-05-2010, 02:42 PM   #37
drowe303
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Im not worried about my gas mileage like your saying I am. I simply asked if everyone was getting around the same numbers as me..

Like I said, this is my second jeep, so gas guzzledge isnt new to me. And I am in no way interested in buying a Suby Baja. But I would love to have an STI!
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Unread 08-05-2010, 04:27 PM   #38
Cavi
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2008 stock with manual and 3:73, I get 17 to 18 consistently, it will sometimes go up to 19, and if I keep it below 70 it goes way up, one trip I did I was following a guy with a trailer so we did at most 60mph and I got 24MPG, so I think I would love the milage if I kept it below 60!!! Not enough self control.....
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Unread 08-05-2010, 04:44 PM   #39
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When I bought my jeep I had a 200+ mile drive home. Thought the thing was going to beat me to death before I got home. I got 18.5 mpg driving 65 mph. That was checked with a calculator, not just the computer reading. Checked the tires the next day and they had 42# pressure. They are stock 245R/75-16 tires. I let them down to 28#. MUCH better ride and I'm still getting 18.5 mpg under the same driving conditions. Set the air pressure in your tires to where you get even tread wear.

An even 22 mpg is the best I've done and 14.8 the worst. I thought the 14.8 was pretty good considering I topped out at 12,888' on a mountain in Colorado and a couple of miles was in 4 low.
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Unread 08-05-2010, 05:17 PM   #40
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Quote:
Originally Posted by jstrubberg View Post
Very true. Unless regearing is preventing you dropping out of overdrive, you gas mileage will go down as gear ratio climbs. You can't run at higher RPM's without using more fuel, all else being equal.
if you put 5.13 in the diffs, with 32" tires, you are correct. if you are running 37" tires on 3.73 gears, you will also lose mileage, due to your engine having to work that much harder to turn your tires.

if you put 5.13 gears, matched with 37" tires (6spd, i'd go 5.88 in an auto, to compensate for d/t power loss), you will find yourself within the factory power band. then you are just losing mpg's from the added weight of all that rubber.

like i said, correct gearing.
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Unread 08-06-2010, 10:40 AM   #41
wimcle
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The JK needs to be cruising down the highway at 2700-3000 rpm. Even if that means never using 5th/6th gears with 3.21 gears!
The torque peak (max efficiency) on this motor is high: 4k rpm.

At 2500rpm you don't make the power to handle wind gusts, small hills, pedestrians...

With 32s, 4.56 gears, and 6speed:
at 3000rpm (74mph) I get 19mpg
at 2700rpm (69mph) I get 22mpg

(I paid real close attention to this when I drove to Colorado last week to test the new gears)
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Unread 08-06-2010, 10:55 AM   #42
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I'm not quite understanding this running at higher RPM thing.

If I set my cruise control for highway speeds on flat stretches it does not run at the RPM ranges I've seen listed.

Getting 18+mpg on the highway, so I'm not sure how running at 3000 RPM is going to make things better. I'm not even sure it would be possible to force it to run that high.

I'm still learning though.
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Unread 08-06-2010, 12:24 PM   #43
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Sounds normal.

The right combination of gears, gas, and a light foot will get up and around the 18 mpg mark.
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Unread 08-06-2010, 12:33 PM   #44
Poor Boy
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Quote:
Originally Posted by McKBrew View Post
I'm not quite understanding this running at higher RPM thing.

If I set my cruise control for highway speeds on flat stretches it does not run at the RPM ranges I've seen listed.

Getting 18+mpg on the highway, so I'm not sure how running at 3000 RPM is going to make things better. I'm not even sure it would be possible to force it to run that high.

I'm still learning though.
you may not be able to get it that high. 3.73 gears are more appropriate for 30" tires. if you put 4.56, or 5.13s in there, you'd be surprised the power you got back. i'm going out. if no one has broken it down by the time i get back, i'll start from beginning to the end
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Quote:
Originally Posted by Hank Venture
It's like someone with a fever is yelling at my pants!
Feed my girlfriend.

Follow my girlfriend

Brew what you drink, drink what you brew

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Unread 08-06-2010, 03:48 PM   #45
jstrubberg
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Quote:
Originally Posted by wimcle View Post
The JK needs to be cruising down the highway at 2700-3000 rpm. Even if that means never using 5th/6th gears with 3.21 gears!
The torque peak (max efficiency) on this motor is high: 4k rpm.

At 2500rpm you don't make the power to handle wind gusts, small hills, pedestrians...

With 32s, 4.56 gears, and 6speed:
at 3000rpm (74mph) I get 19mpg
at 2700rpm (69mph) I get 22mpg

(I paid real close attention to this when I drove to Colorado last week to test the new gears)

There is no way you can run at 4k RPM and improve gas mileage. None.

Don't believe me? Automatic owners, turn off overdrive, drive 50 miles, then turn it back on and do the same. Report your mileage.

If running at high RPMs meant better CAFE numbers, I guarantee you noone would have gone to the trouble or expense to come up with a 6 speed tranny to keep RPMs down!
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3.8L V6 , 35" tires , JK Wrangler , mileage , miles per gallon , mpg , wrangler
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