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Old 03-22-2013, 04:12 PM   #1
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05 Rubicon Unlimited gearing/speed question

I sold my scrambler and picked up a 2005 rubicon unlimited. It has a rubicon express 3.5 inch lift and 33x12.50 15 rites on 15 x 8 mickey thompson wheels. The jeep only has 17500 miles. It is supposed to have the factory gearing of 4.10s but at 65 on the speedo which is actually 69 per the gps I am turning 2500-2600 rpms. Anybody else getting the same numbers with similar set up?

This thing is a complete gas hog. My scrambler had 33's and a tune port 350 with a 4 speed and was a prius compared to my new to me purchase.

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Old 03-22-2013, 04:38 PM   #2
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I'm doing about the same RPM's with mine. Similar setup.

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Old 03-22-2013, 05:37 PM   #3
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which transmission?
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Old 03-22-2013, 06:27 PM   #4
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Check, check, check... we have the Jeep (except mine is an 04), lift, wheels and tires. At 65mph indicated (gps says 68), I'm turning 2,000 rpm.

Mine is a 5-speed manual. But final ratio of the NV3550 transmission is the same whether a 5 speed (2003-2004) or 6 speed (2005-2006). I'm not sure about the final ratio on automatics.
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Old 03-22-2013, 07:21 PM   #5
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Yours being a Rubicon has the 4 spd and overdrive. Guessing stick? You lost some dropping from a 16" to 15", but then what, 2" bigger on the tire dia? I have a bone stock Rubicon w/auto and it's at 2K @ 65 Mph.
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Old 03-22-2013, 07:38 PM   #6
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its a 6 speed manual. if I had the 16 inch stock wheel with the same overall diameter that I have now, wouldn't my numbers be the same as I have now?
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Old 03-22-2013, 08:44 PM   #7
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It has nothing to do with the trans. or the gearing in this case. When Jeep builds the vehicle the speedometer is calibrated to the size of the tires and gearing. When you install bigger tires or re gear the speedometer will be off. It looks like the tires are reason. Stock 31s circumference is about 97 inches and the 33s are about 103. The speedo sees 97 inches per revolution (65) and you are actually going 103 (69) inches per revolution.
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Old 03-22-2013, 09:22 PM   #8
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speedo is off.

stock 4.11's with the 6-speed is fine for 33s.

buy a speedo recalibration tool, like the Speedohealer, Dakota Digital, etc, and fix the speedo.
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Old 03-22-2013, 09:32 PM   #9
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I am not questioning the speed. I believe my dash mounted GPS is on the money in terms of the speed. It just seems to be really rung out rpm wise to go only 69 mph like the dash mounted GPS is saying. I just figured with adding the taller tire is would have reduced the rpm in relation to the speed traveled. I hate to think what a stocker is spinning at the same speed. Or is my mind full of mud?
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Old 03-22-2013, 09:33 PM   #10
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Quote:
Originally Posted by lavern23 View Post
I am not questioning the speed. I believe my dash mounted GPS is on the money in terms of the speed. It just seems to be really rung out rpm wise to go only 69 mph like the dash mounted GPS is saying. I just figured with adding the taller tire is would have reduced the rpm in relation to the speed traveled. I hate to think what a stocker is spinning at the same speed. Or is my mind full of mud?
mud.

the rpms are fine
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Old 03-22-2013, 09:54 PM   #11
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If you didn't recall your speedo that would seem to be the reason for the false readings. You say same overall tire dia? from Stock 245/75/16 Vs = to a 33/12:50-15? really? If your overall tire diameter gets bigger, its should be more sluggish and readings higher. Smaller diameter and readings should be lower (better low end snap). Recall speedo would seem to be needed.
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Old 03-22-2013, 10:02 PM   #12
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I guess I wasn't clear on the tire size comparison. I was meaning same size overall if I had the 16 inch with 33s vs 15 inch wheels with 33s. It's the overall diameter of the wheel that changes the pep, snap, etc... If you don't re gear. I am just wanting to know if those with similar set up have the same numbers. I purchased this Jeep as is and would have thought that the addition of the tires in this diameter would have made it better on the highway in terms of the Rpms in relation to the speed. Meaning lower rpm number.
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Old 03-22-2013, 10:04 PM   #13
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Same here def tire size plays into the speedmeter
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Old 03-22-2013, 10:33 PM   #14
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Yeah, the comparison is the "overall" dia of the tires. Does't really matter the wheel size, really. A 245/75/16 shows @ 30.5" dia, a 33/12:50-15 Is roughly well 33" (tires dia's differ by brand) so aprox a 2-1/2" dif... "that's significant"... At that dif, your going to see & feel the difference in response and economy (turdy/sluggish feel Etc).
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Old 03-22-2013, 10:46 PM   #15
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Similar, but I'm running 35's on my Rubi LJ. I can watch the gas needle move to the E lol
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Old 03-22-2013, 10:55 PM   #16
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Sounds about right for 4.10's. My '04 5spd indicates 65 and 2150rpm when it's doing 71. 4.10 gears and 35's. Makes sense that 33's would bump the revs up a bit, and push the speedo off slightly less.
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Old 03-22-2013, 10:56 PM   #17
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Quote:
Originally Posted by lavern23 View Post
I am not questioning the speed. I believe my dash mounted GPS is on the money in terms of the speed. It just seems to be really rung out rpm wise to go only 69 mph like the dash mounted GPS is saying. I just figured with adding the taller tire is would have reduced the rpm in relation to the speed traveled. I hate to think what a stocker is spinning at the same speed. Or is my mind full of mud?
You're correct- stock rubicons on 245/75/16 tires run higher rpm at that same speed. Speedometer correction aside, mine ran about 3,000 rpm on the stock tires at 70 mph (GPS reading). After I went to 33's, the rpms dropped down to just over 2,250 rpm at 70 mph (GPS reading).

I personally think they were geared too low from the factory for 245/75/16s (just under a 31" tire). I rarely used 1st gear on streets. I think the 4.11 gearing with 33's is perfect for on-road driving.
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Old 03-22-2013, 11:55 PM   #18
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Oh ya. Our 06 is almost exactly like yours. I find the best way to deal with the problem is to not measure the gas mileage. All kidding aside, unless you calibrate your odometer to your tires, how do you know what MPG your really getting?
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Old 03-23-2013, 05:02 AM   #19
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Oh ya. Our 06 is almost exactly like yours. I find the best way to deal with the problem is to not measure the gas mileage. All kidding aside, unless you calibrate your odometer to your tires, how do you know what MPG your really getting?
Well.........for the price of a speedometer re-calibrator you can get a very nice GPS that will not only accurately read out your speed abut will keep track of the actual mileage you travel on each tank of gas...............Just sayin'
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Old 03-23-2013, 06:08 AM   #20
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Actually switching speedo Gear in MOST TJs is about a 20 min $40 job....OP I understand what you are saying, I have 3.73s and 33's in an '04..and while not the same, and I have had "discussions" on here in the past, I like it when my tach is about 1750-2000rpm.......but alot of people think nothing of winding it up to 3K and running down the highway...they will try and convince you that is where the I6 likes to be/ run for best MPGs
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Old 03-23-2013, 07:52 AM   #21
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What are getting for gas milage on highway? Im running 35 on my Rubi LJ also and calculated 13 mpg on a summer vacation trip while highway driving.

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Originally Posted by DetroitRodeo View Post
Similar, but I'm running 35's on my Rubi LJ. I can watch the gas needle move to the E lol
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Old 03-23-2013, 07:56 AM   #22
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Quote:
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Oh ya. Our 06 is almost exactly like yours. I find the best way to deal with the problem is to not measure the gas mileage. All kidding aside, unless you calibrate your odometer to your tires, how do you know what MPG your really getting?
GPS. Fill your gas tank, reset trip milage on GPS. Go 100-150 miles on highway and refill tank to determine gallons used. Then calculate.
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Old 03-23-2013, 09:02 AM   #23
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What are getting for gas milage on highway? Im running 35 on my Rubi LJ also and calculated 13 mpg on a summer vacation trip while highway driving.
I've never calculated it to be honest....something to do this weekend!
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Old 03-23-2013, 09:56 AM   #24
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If you know that you speedo is off 5 mpg at 50 you can add 5 miles for every 50 miles that you travel or figure out the percentage. This would add 10%. Per speedo and gallons calcuates at 15 mpg, actual mpg is 16.5. Not going to be that easy in most cases.
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Old 03-26-2013, 09:43 AM   #25
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The only time I ran it on the freeway long enough to get a true reading was when I drove it home after buying it around 500 miles away. I got 18.75 MPG at around 72 - 74 MPH with the cruise.

I was running 31's at the time with the stock 4:11 Rubi gearing and 4 speed auto.

I seem to be getting 10 - 12 around town with lots of short trips, stop signs etc..

All of these numbers are based on the GPS as I now read about 5% low on the factory speedo and have no intention of buying a re-calibration device as I'll probably go to at least 33's and maybe 35 in a year or 2 when the current tires wear out......and I have a better idea of just how much off-roading I will be doing.
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Old 03-26-2013, 09:48 AM   #26
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Originally Posted by lavern23 View Post
I sold my scrambler and picked up a 2005 Rubicon unlimited. It has a Rubicon express 3.5 inch lift and 33x12.50 15 rites on 15 x 8 mickey thompson wheels. The jeep only has 17500 miles. It is supposed to have the factory gearing of 4.10s but at 65 on the speedo which is actually 69 per the GPS I am turning 2500-2600 rpms. Anybody else getting the same numbers with similar set up?

This thing is a complete gas hog. My scrambler had 33's and a tune port 350 with a 4 speed and was a prius compared to my new to me purchase.
my 06 with auto and 32's runs almost exactly 2K RPMs at 65 MPH (GPS).....my friends 06 with 6 speed runs almost exactly like yours with the 6 speed.

I looked it up and the final drive in the 6 speed is .84 and the Auto is .68.....obviously this is the difference. Not sure how this affects mileage but one would think that the auto might get better mileage than the 6 speed.....does anyone know if this is the case in the "Real World"??
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Old 03-06-2014, 01:43 AM   #27
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I have an 05 Rubi, auto trans, on 35x12.50x15, I'm assuming it has the stock gearing of 4.11.

•Odometer is -0.115 per mile avg. @ 100 miles (GPS) <miles: 88.5odo=100gps, 177odo=200gps>*

• RPM Speed
-1500 RPM @52 MPH
-1750 RPM @60 MPH
-2000 RPM @69 MPH
-2250 RPM @79 MPH

*-To figure MPG, multiply odometer miles by 0.115, add that number back to odometer miles (+3), and divide by gallons of fuel used. Example below from my last tank of gas / fill up:
193.1x.115=22.2
22.2+193.1=215.3
215.3+3=218.3
218.3/16.135gal=13.5MPG
(Actual GPS mileage was 218.5)

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