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Old 02-18-2015, 08:40 AM   #99
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Picked up the truck yesterday afternoon and just drove it home. It seems at 60 or so in sixth gear it has only increased the RPM by 100, so should not make any major difference in highway fuel mileage. I did notice the gear change more at lower speeds in the lower transmission gears, which makes sense to me, and this should give me what I wanted..... more power at lower hill climbing speeds.
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Old 02-18-2015, 11:10 AM   #100
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Question for owners of late model Ram 2500 6.7 Cummins Diesel Owners

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I have not. There have been too many variables in different trailers, different tire sizes, and different areas driven.

I just know the best I ever got on a long trip without the trailer was 19.5, and that was all highway with speeds up to 80, but mostly 75.

With tail winds pulling the 31 at mostly 67-70 it would get 14, but not with the 34. More like 9 to 10.5.

Everyone would like to get good fuel mileage, but it's not my primary concern.

Tracking fuel burn versus miles is one of the simplest ways of monitoring truck health, it is not just cost accounting. Engine hours versus miles gives average mph. Those two numbers -- average mpg and average mph -- tell quite a lot about present and likely future costs.

A gear ratio change affects one of them specifically.

If this is a dedicated TV, then analysis is pretty easy.
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Old 02-18-2015, 11:24 AM   #101
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Picked up the truck yesterday afternoon and just drove it home. It seems at 60 or so in sixth gear it has only increased the RPM by 100, so should not make any major difference in highway fuel mileage. I did notice the gear change more at lower speeds in the lower transmission gears, which makes sense to me, and this should give me what I wanted..... more power at lower hill climbing speeds.

I imagined you'd enjoy the change. Though it really makes no difference on what the truck can do outside of higher altitude driving. About the only reason I hesitate in changing mine is a consideration of changing my home to such a place.

There are gear ratio calculators online that will give exact change. If one likes to tow at 60-mph, the rpm will be clear as to the difference made by the ratio change. Worthwhile to see if the prediction is met.

The auto trans is essentially a 4+2 arrangement as I recall. Two overdrive gears. Or, why I wish my truck had a seventh gear: one OD for towing on the flats, and a second higher OD gear for running empty/solo.

What is your predicted 60-mph rpm and actual?

My 10k rated trailering & 13k GN/5er GCVWR is 20k with 3.73 gears and I run 60-mph right under 1,800-rpm when in Overdrive. I'll check the Direct rpm at 60-mph today as I can't remember the number.
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Old 02-18-2015, 11:36 AM   #102
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My truck has the 3:73 gears. I find that 65 - 68 mph on the interstate seems to be a good mph to tow that has the least amount of transmission shifting on the hills. You truck may do better since it has slightly more horsepower and much more torque than my 09.
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Old 02-18-2015, 01:01 PM   #103
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In this 2004 305/555 CTD with six speed manual:

60 is a few hairs shy of 1,800-rpm in Overdrive.

And right under 2,400-rpm in Direct.

With that double OD in yours you can see why theoretically an auto trans truck otherwise the same could get better mpg on the highway. The manual trans in your year model is from a different supplier and has a longer OD gear. But still not as long as the 68 auto.

All this sums to different engine computer programming between auto and manual, but the change you've made shouldn't much affect it. I'd guess you've moved from one edge of the envelope to the other for an auto trans truck where 4.10 is not available. A half step versus a full step in change.

Fuel burn is just a way of looking to regen cycle frequency, etc.
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Old 02-18-2015, 01:33 PM   #104
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At about 60 mine was turning 1600 yesterday. In the past, I've noticed the best fuel mileage on the highway at 1700-1800 RPM.
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Old 02-18-2015, 07:19 PM   #105
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That is about right ,mine runs 60-65 at a1500-1600, speedo might be a little fast according to the garmin, I would like to try the 3.42 , I did have a 4.10 with a 7.3 and a 5 speed , 2200 running about 62 , not good. My model a had 4.11, and I changed it to 3.54, I like it better.
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Old 02-19-2015, 05:11 PM   #106
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We just bought a 2015 Ford F-250 diesel long bed after having a Ford F-150 EcoBoost. My hubby thought it was pretty funny that shortly after our purchase I came home with the newest issue of "Diesel Power" Magazine. To your point this article talks about the mystery of to how to determine the Gross Combined Weight Rating (GCWR) of a vehicle and trailer combination. Apparently they are going to standardize this so you can shop and compare vehicle to vehicle. SAE J2807 Tow Tests - The Standard
Maybe I'll subscribe!
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Old 02-20-2015, 03:56 AM   #107
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The J2807 Towing Standards have been around since 2009 when they were agreed to by the auto manufacturers beginning with the 2013 model year; however there has been some "back pedaling" mainly by Ford.
http://www.autonews.com/article/2013...-isnt-standard

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Old 02-20-2015, 08:05 AM   #108
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The J2807 Towing Standards have been around since 2009 when they were agreed to by the auto manufacturers beginning with the 2013 model year; however there has been some "back pedaling" mainly by Ford.
http://www.autonews.com/article/2013...-isnt-standard

Bill
Not saying it's not true, but that article is dated February 11, 2013, or over two years ago.

It would be interesting to know for sure what all the manufacturers are doing today.
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Old 02-20-2015, 09:58 AM   #109
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I believe Ford/GM/Ram are J2807 compliant with the 2015 models. Toyota adopted the standard immediately. Nissan will be compliant with 2016 models.
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Old 03-08-2015, 01:56 PM   #110
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OK, went to a rally this weekend of about 300 miles round trip, and if anyone is interested, the truck towed the trailer noticeably better with the 3.73 gears, but I won't say significantly better. Winds were not good for checking fuel mileage, but it looks to be about the same.
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Old 03-09-2015, 01:43 AM   #111
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When ever one spends some monies on something ,that alone will make it better!
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