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 > Need some advice, gearing/fuel mileage.

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MikeRP

Westerville

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Posted: 10/28/20 06:18pm Link  |  Quote  |  Print  |  Notify Moderator

Hey

I know we have a big thread on fuel mileage going. I’m considering a 2020 Ram 3500 Crew Cab with the HO Cummins/Aisin and it has the 4.10 gears and it’s a dually. On a test drive it appeared to be doing around 2000 rpm at 70 mph.

My 2018 3500 is a SRW SB with the HO Aisin and it gets 18-20 in mixed driving and 11 mpg towing my 14,500 lb fifth wheel with the 3.42 gears.

Looks like these sales guys are ordering 4.10’s on everything but I could go w 3.73 gears and hopefully some better fuel mileage.

I tow usually around 65-68 mph. Like I said any ideas on the fuel mileage for this new truck? I live in Ohio and I try to generally stay within the speed limits.

Lwiddis

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Posted: 10/28/20 06:35pm Link  |  Quote  |  Print  |  Notify Moderator

If improving mileage is your priority, decrease your speed to 55 mph. “If combined truck/trailer combo exceeds 8,000 lbs, speed limit is 55 mph.” See...

https://drivinglaws.aaa.com/tag/trailer-speed-limits/


Winnebago 2101DS TT & 2020 Chevy Silverado 1500 LTZ Z71, 300 watt solar-parallel & MPPT, Trojan T-125s. TALL flag pole. Prefer USFS, COE, BLM, NPS, TVA, state & county camps. Bicyclist! 14 year Army vet-11B40 then 11A - (MOS 1542 & 1560) IOBC & IOAC grad


jdc1

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Posted: 10/28/20 07:45pm Link  |  Quote  |  Print  |  Notify Moderator

Well, let's start with Ohio's 55mph towing speed limit......That alone will improve your mileage by 15% or more.

ksss

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Posted: 10/28/20 07:54pm Link  |  Quote  |  Print  |  Notify Moderator

jdc1 wrote:

Well, let's start with Ohio's 55mph towing speed limit......That alone will improve your mileage by 15% or more.



And increase your road rage factor by 150%. Pulling a trailer in Cali is extremely frustrating.


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ShinerBock

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Posted: 10/28/20 07:54pm Link  |  Quote  |  Print  |  Notify Moderator

Not sure what your power/towing requirements are. If mileage is your utmost concern then I would not get the HO or performance series as it is called in the medium duty world. The standard output(efficiency series in medium duty trucks) will net you better fuel economy due to it's much higher compression ratio of 19:1 versus 16.2:1 of the HO.

MikeRP

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Posted: 10/28/20 08:13pm Link  |  Quote  |  Print  |  Notify Moderator

Jdc1: Ohio hasn’t been 55 for a long time. I think it is 65 mph now on Freeways.

ShinerBock: you are right I will consider stepping back to the standard Cummins and the 3.73. Plenty enough to tow 14,500 lbs.

jdc1

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Posted: 10/28/20 08:17pm Link  |  Quote  |  Print  |  Notify Moderator

MikeRP wrote:

Jdc1: Ohio hasn’t been 55 for a long time. I think it is 65 mph now on Freeways.

ShinerBock: you are right I will consider stepping back to the standard Cummins and the 3.73. Plenty enough to tow 14,500 lbs.



I just looked it up.....towing speed limit in Ohio is 55mph.

mkirsch

Rochester, NY

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Posted: 10/29/20 06:23am Link  |  Quote  |  Print  |  Notify Moderator

jdc1 wrote:

MikeRP wrote:

Jdc1: Ohio hasn’t been 55 for a long time. I think it is 65 mph now on Freeways.

ShinerBock: you are right I will consider stepping back to the standard Cummins and the 3.73. Plenty enough to tow 14,500 lbs.



I just looked it up.....towing speed limit in Ohio is 55mph.


That's on secondary roads. On expressways like I-80 it's 65, but the regular speed limit is 75, so you're still getting passed by like you're standing still.


Putting 10-ply tires on half ton trucks since aught-four.

valhalla360

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Posted: 10/29/20 07:06am Link  |  Quote  |  Print  |  Notify Moderator

jdc1 wrote:

Well, let's start with Ohio's 55mph towing speed limit......That alone will improve your mileage by 15% or more.


Not always...depends on the full power train and where it's optimized.

Not sure on the specifics of the Dodge but with a 2008 V10 F250 (I realize it's not apples to apples), running at 55mph has the drivetrain struggling to hold overdrive. Bump it up to 60-65mph and it holds nicely and we get an extra 1 MPG. Much above that and MPG quickly goes back down.


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otrfun

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Posted: 10/29/20 08:45am Link  |  Quote  |  Print  |  Notify Moderator

Our '16 Ram Cummins' overall gearing in 5th gear with a 3.42 rear end is more or less equivalent to a 4.10 in 6th gear. After numerous cross-country trips with various 10k-12k 5th wheels and TT's we've noticed no difference in fuel economy driving at 65 mph in 5th or 6th gear. We always tow in 5th to reduce downshifting (and wear and tear to the tranny) and to keep the Cummins more responsive (at 65 in 5th it's at 1,700 - 1,800 rpm, operating at peak torque). Another added plus, the exhaust brake is also much more responsive.

IMO, the only situation where the 3.42 or 3.73 gears *may* have an mpg advantage is driving at 80 mph EMPTY in 6th. I could see a possible 1 mpg increase in fuel economy vs. a 4.10 in 6th at 80 mph.

Me, I can't see the logic in purchasing a $70k-$80k truck that's main purpose in life is towing/hauling heavy, then reduce its tow capacity via higher driveline stress with a 3.42 rear end . . . over a possible or, at most, a negligible increase in fuel economy. IMO, it's a no-brainer to go 4.10---unless your main goal is a slight increase in fuel economy driving at 80 mph EMPTY.

YMMV.

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