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 ?

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.

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.

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.

valhalla360 wrote:You do realize the newer trucks have an 8 speed transmission, The diesels don't.

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.

2020 Ram 2500 CTD owners | Good Sam Community

17 Replies

CaLBaR
Explorer II
May 20, 2020
Me Again wrote:
So when I was towing the 5th wheel at 24,500 combined I towed at 60 MPH in 5th. Then came the little commuter TT with a combined 16K weight, and towing at 60 in 5th it got almost the same mileage was the heavier 5th wheel. So I have learned to tow without TH in slower areas like California and let it shift to 6th gear. In Az, Or and Wa I towed at 65-66 in 6th and mileage was better.

Thanks for the input. This sounds like a good idea as the Cummins and Aisin only shift to 6th over about 64 to 65 MPH from what I have noticed in tow/haul mode and I highly doubt that towing a 10,000 lb bumper pull will be a problem in 6th at 60 MPH.

Rob
Me_Again
Explorer III
May 19, 2020
So when I was towing the 5th wheel at 24,500 combined I towed at 60 MPH in 5th. Then came the little commuter TT with a combined 16K weight, and towing at 60 in 5th it got almost the same mileage was the heavier 5th wheel. So I have learned to tow without TH in slower areas like California and let it shift to 6th gear. In Az, Or and Wa I towed at 65-66 in 6th and mileage was better.
Cummins12V98
Explorer III
May 19, 2020
YES, I screwed up! I was looking for my pic with it in 5th gear.
bucky
Explorer II
May 19, 2020
NJRVer wrote:
??? Looks like about 1400 at 62:)

Got him!
Flan
Explorer
May 18, 2020
Was just out on the highway, 2019 6.7 2500 3.73s 68rfe

1800 in 6th 70mph
2375 in 5th 70mph
NJRVer
Explorer
May 18, 2020
??? Looks like about 1400 at 62:)
Cummins12V98
Explorer III
May 18, 2020
Looks like about 1,375 @ 62mph.
valhalla360
Navigator
May 18, 2020
ShinerBock wrote:
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.

Caught me on that one.

In that case 9% higher with the different rear end.
JKJavelin
Explorer III
May 18, 2020
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
Cummins12V98
Explorer III
May 18, 2020
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.