Need some advice, gearing/fuel mileage.

"Pulling a trailer in Cali is extremely frustrating."

That's you, KSSS. 55 mph is safer...you see more...you save on gasoline.

otrfun wrote:
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.

Good post!

I think a lot of the need or want for better fuel economy depends on how it will be used and how often the truck will be loaded/unloaded.

For the first 2-3 years of ownership, I used my truck as a daily 40 miles one way commuter, towing various trailers ranging from 4k-13k, and countless trips to the farm(50 miles away) and deer lease(153 miles away). I was putting around 30k miles on my truck a year during that time and fuel was about $3.00 a gallon. Slight mpg improvements had more of an impact due to how I was using the truck back then so a 3.42 was a no brainer even if another option was available. Now I have a diesel commuter car that gets 45 mpg so the fuel economy in my truck is not as important as it was back then even though I still like to get the best mpg possible for how I am using it. If I would have had my car back when I bought my truck, I would probably gone with the shortest gear available. However, the 3.42 was the only option.

I've towed a 19,000 pound trailer all over the country with 3.73 gears. Sure it might by nice to have lower gearing in the mountains but 3.73 is a nice compromise. Frankly, I don't concern myself with fuel mileage. If I did, I wouldn't be towing in the first place.

According to the BSFC map for the 6.7 Cummins that Shiner posted on another thread the 3.42 pulling in 5th vs 4.10 in sixth yield very similar MPG while towing. 3.42's should yield close to 10% better fuel economy while running empty at virtually any highway speed. Again, according to the same BSFC map, towing with 3.73 gears at 65 mph should offer a slight advantage in MPG over either 3.42's or 4.10's. Empty the 3.73 will fall half way between 3.42's and 4.10's.

I agree with Shiner in that it comes down to how you will use the truck ... if you run empty a fair bit 3.42's make sense. (I'd have a hard time not going for 3.42 no matter what) but if you're normally towing at 65 mph I'd go with 3.73's over 4.10's.

I also agree with Shiner that if you don't require the HO Cummins the regular output should do a little better on fuel.

RVing and fuel mileage isn’t a thing. Have fun.

MikeRP wrote:
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.

What the heck are they planning of hauling !

That a lot revs for that Cummins !

4x4ord wrote:
According to the BSFC map for the 6.7 Cummins that Shiner posted on another thread the 3.42 pulling in 5th vs 4.10 in sixth yield very similar MPG while towing. 3.42's should yield close to 10% better fuel economy while running empty at virtually any highway speed. Again, according to the same BSFC map, towing with 3.73 gears at 65 mph should offer a slight advantage in MPG over either 3.42's or 4.10's. Empty the 3.73 will fall half way between 3.42's and 4.10's . . .

"3.42's should yield close to 10% better fuel economy while running empty at virtually any highway speed" vs. a 4.10. Interesting. Not what I've experienced.

Are you making these observations based on BSFC maps of the crankshaft output of a Cummins in conjunction with gearing charts?

Or, are your observations based on BSFC maps formulated and based on on-the-road tests of production-ready, OEM Ram trucks? If so, I'd be very interested in seeing these. Could you supply a link? Thanks.

Wow everyone I appreciate the feedback a lot. My 2018 has only towed 10-11% of the time. So I have 57,000 miles on it and have towed I my slightly over 5800 miles.

I think, even though I want it to be more, I think the next three years I wil be towing 10,000-12000 miles per year for a total or around 25,000 miles per years w my Camper getting heavier, generator and combo washer dryer installed, as well as more stuff for longer trips.

So I will add another 500-750 lbs and the GVWR of the Cedar Creek is 16,2XX lbs.

I’m falling in love w this truck so unless someone talks me out of 4.10’s, I’ll probably make an offer.

Doesn’t seem like something to get worked up over now? Right? I’d be ordering 3.73’s instead of buying this one w 4.10’s if you talk me out of 4.10’s. Thanks for feedback.

Mike

If your tow vehicle of choice is marginal, go with 4.10's

If your tow vehicle of choice is formidable, then gears start to matter less, especially with newer 8 - 10 spd transmissions.

otrfun wrote:

4x4ord wrote:
According to the BSFC map for the 6.7 Cummins that Shiner posted on another thread the 3.42 pulling in 5th vs 4.10 in sixth yield very similar MPG while towing. 3.42's should yield close to 10% better fuel economy while running empty at virtually any highway speed. Again, according to the same BSFC map, towing with 3.73 gears at 65 mph should offer a slight advantage in MPG over either 3.42's or 4.10's. Empty the 3.73 will fall half way between 3.42's and 4.10's . . .

"3.42's should yield close to 10% better fuel economy while running empty at virtually any highway speed" vs. a 4.10. Interesting. Not what I've experienced.

Are you making these observations based on BSFC maps of the crankshaft output of a Cummins in conjunction with gearing charts?

Or, are your observations based on BSFC maps formulated and based on on-the-road tests of production-ready, OEM Ram trucks? If so, I'd be very interested in seeing these. Could you supply a link? Thanks.

I think part of the discrepancy here is emissions controls. Looking back at the report from where I got the BSFC map from, it does not mention emissions so the map may be without them since they are somewhat of an unknown variable. I do know that the EGR will open more under moderate load at low rpms as the combustion temps rise(which correlates to higher EGT's) since NOx creation rises significantly at 2,800F.

The EGR introduces spent exhaust gases that is already deprived of oxygen which has a major impact on the engines efficiency. It does not do this at higher rpms because the engine is receiving more air for the amount of fuel being injected to make the same horsepower and the higher rpms also allow more air to flow through the engine at a faster rate. Hence the reason why EGT's decreases when you shift into a lower gear putting you at a higher rpm.

Another factor is that the more cooled exhaust gases introduced, the more soot it creates which clogs up the DPF quicker. Clogging up the DPF quicker means it will need to regen sooner than normal. If the DPF is not hot enough to regen then it will perform an active regen and inject extra fuel on the exhaust stroke to heat up the DPF(at least for Ford and Cummins engines) so it is using more fuel than normal.

This may be a factor into why the BSFC maps may not align with what is happening in the real world. Especially when outside air temps are in or near triple digits since the temperature of the ambient temps have a significant impact on combustion temps and EGT's. As ambient air goes up, so will EGT's/combustion temps and the EGR will activate accordingly to keep NOx generation low. The more it activates, the less efficient the engine is because it is receiving less clean air with less oxygen. Our northern friends in cooler climates may not have to deal with this as much.