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M.R.E.

MI, usa

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Posted: 05/18/20 08:50am Link  |  Quote  |  Print  |  Notify Moderator

I have a '16 Ram 2500 CTD that I love except towing. I wish it had the 3.73 rearend instead of the 3.42. What is your rpm at 7o mph in 5th and 6th gears ?


toolmaker

valhalla360

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Posted: 05/18/20 10:03am Link  |  Quote  |  Print  |  Notify Moderator

M.R.E. wrote:

I have a '16 Ram 2500 CTD that I love except towing. I wish it had the 3.73 rearend instead of the 3.42. What is your rpm at 7o mph in 5th and 6th gears ?


You do realize the newer trucks have an 8 speed transmission, be careful that you are comparing apples to apples. The link below shows the gear ratios.

https://www.cars.com/research/ram-2500/specs/

Assuming you pick a transmission gear ratio that is the same (it might not be exactly the same)...going from 3.42 to 3.73, should bump the RPM up by about 9% but in reality, the newer truck will likely select a different gear such that the overall gear ratio from crank shaft to wheel stays where the engine is happiest and with more gears to choose from, it can do a better job.


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ShinerBock

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Posted: 05/18/20 10:06am Link  |  Quote  |  Print  |  Notify Moderator

The math is telling me that a 3.73 CTD with a 68RFE at 70 mph, 5th will put you at 2,170 rpm (which is too high IMO) and 6th with put you at 1,652 rpm (which is too low for EGT's). The 3.42 rear end at 70 mph in 5th is around 1,990 which is ideal rpm to keep EGT's low without revving higher than necessary. This is why many recommend towing in 5th with 3.42 gears which will actually have more torque multiplication than a 3.73 geared truck in 6th while putting you at the most efficient rpms for towing per Cummins.

ShinerBock

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Posted: 05/18/20 10:07am Link  |  Quote  |  Print  |  Notify Moderator

valhalla360 wrote:

M.R.E. wrote:

I have a '16 Ram 2500 CTD that I love except towing. I wish it had the 3.73 rearend instead of the 3.42. What is your rpm at 7o mph in 5th and 6th gears ?


You do realize the newer trucks have an 8 speed transmission, be careful that you are comparing apples to apples.



Only the gas engines have the 8 speed. The diesel's have the same 6 speed trans as previous year models.

Grit dog

Black Diamond, WA

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Posted: 05/18/20 10:21am Link  |  Quote  |  Print  |  Notify Moderator

valhalla360 wrote:



You do realize the newer trucks have an 8 speed transmission,


The diesels don't.


"Yes Sir, Oct 10 1888, Those poor school children froze to death in their tracks. They did not even find them until Spring. Especially hard hit were the ones who had to trek uphill to school both ways, with no shoes." -Bert A.

Groover

Pulaski, TN

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Posted: 05/18/20 10:38am Link  |  Quote  |  Print  |  Notify Moderator

You would be looking at only a 9% increase going to the lower gear ratio, barely noticeable. As ShinerBock said, just lock out 6th gear when towing unless you have some other reasons for changing the gears. That way the engine will turn a more reasonable speed when not towing too. And don't forget that tire size affects rpm as well. Newer trucks seem to be trending towards larger tires so they need the lower gears to get the same power to the ground at any given speed.

Cummins12V98

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Posted: 05/18/20 11:19am Link  |  Quote  |  Print  |  Notify Moderator

M.R.E. wrote:

I have a '16 Ram 2500 CTD that I love except towing. I wish it had the 3.73 rearend instead of the 3.42. What is your rpm at 7o mph in 5th and 6th gears ?


PLEASE explain what you don't like. You towing at 70 all the time?


2015 RAM LongHorn 3500 Dually CrewCab 4X4 CUMMINS/AISIN RearAir 385HP/865TQ 4:10's
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Cummins12V98

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Posted: 05/18/20 11:20am Link  |  Quote  |  Print  |  Notify Moderator

"You do realize the newer trucks have an 8 speed transmission"

You know something I don't know???

Cummins12V98

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Posted: 05/18/20 11:25am Link  |  Quote  |  Print  |  Notify Moderator

My 11 HO DRW had 3.42's and I loved them. ONLY issue was getting the load rolling on a steep grade with the 68RFE. AISIN cures that issue. I was only towing a combined 29k.

I towed in 5th at 1,750rpm at 60. SAME rpm as my current DRW with 4.10's at 60. PERFECT rpm's.

IMHO 3.73's are the bastard gearing in the 4th gen trucks.

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JKJavelin

Milwaukee, WI

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Posted: 05/18/20 11:55am Link  |  Quote  |  Print  |  Notify Moderator

2018 Ram Cummins 3.42
When towing my 11,000 5er, if I let it shift into 6th at around 1200 rpm @65 mph, anything more than a slight uphill grade, will cause it to drop to 5th gear. If I keep it in 5th gear, around 1700 rpm @65 mph, it will stay in 5th for most hills...not talking mountains here.
So most of the time I keep it in 5th and I usually use the cruise control.
JK


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