Highway Engine RPM

[turretplug]

What is ideal engine rpm for highway mileage at 60-70 mph? I have 35” tires with only a REVTEK leveling kit for clearance. I changed gears from the stock to 4.56 to give me better hill towing performance. Towing a 7000lb travel trailer I average about 9.5 mph. Empty I only average around 15.5mph. Unload rpm at 65mph is 1950. I also changed out the entire induction system minus the turbo for the banks products. Looking to improve my mileage both towing and unloaded.

2016 3500 4x4 Crew Cab w/long box, Automatic.
Jon

 

[Mikey-KE7LBB]

With as light as that trailer is, 3.73 would've been more than adequate, even with the larger tires.

 

[AH64ID]

What is ideal engine rpm for highway mileage at 60-70 mph? I have 35” tires with only a REVTEK leveling kit for clearance. I changed gears from the stock to 4.56 to give me better hill towing performance. Towing a 7000lb travel trailer I average about 9.5 mph. Empty I only average around 15.5mph. Unload rpm at 65mph is 1950. I also changed out the entire induction system minus the turbo for the banks products. Looking to improve my mileage both towing and unloaded.

2016 3500 4x4 Crew Cab w/long box, Automatic.
Jon

That’s a huge gearing change for 35’s. 33% lower gears for a tire that’s not even 5% larger than stock.

Best mileage empty would probably be with 3.73’s, and towing either 3.73’s or 4.10’s. That would around 1550-1650 at 65.

Did you adjust your speedo? 1950 rpms should be closer to 68-70 mph with 35’s and 4.56.

None of those intake mods will net you any appreciable fuel economy gains as the stock setup already flows more than enough air especially while cruising empty. Certainly never enough to cover the cost.

 

[Ozymandias]

You know that your truck was geared right for perfect milage and pulling power right from the factory?
Even with the 35er it was just perfect.
4,56 may be right for a gasser that screams down the road with 6000rpm like my buddy's 2500 HEMI but for a Diesel that decision was the wrong one, sorry. You'll never get that milage back that you sacrificed with that gearing.

 

[kthaxton]

Yeah, you're over geared.

 

[bcbender]

I had 4:10s in my 04 pulling 20k and I never thought I needed more... in fact often wished I had the 3:73s..

 

[Turbo Terry]

I thought that’s why you bought a diesel for the torque to pull grades etc

 

[turretplug]

That’s a huge gearing change for 35’s. 33% lower gears for a tire that’s not even 5% larger than stock.

Best mileage empty would probably be with 3.73’s, and towing either 3.73’s or 4.10’s. That would around 1550-1650 at 65.

Did you adjust your speedo? 1950 rpms should be closer to 68-70 mph with 35’s and 4.56.

None of those intake mods will net you any appreciable fuel economy gains as the stock setup already flows more than enough air especially while cruising empty. Certainly never enough to cover the cost.

Speedo has been properly calibrated for the larger tires. When I made the change to larger tires years ago it was definitely a hit to both mileage unloaded and towing. It also made for poor towing performance in the mountains of the west which is where I live and do the majority of my camping. Transmission would constantly be dropping two gears at least on grade even in tow/haul mode, long grades would put EGTs up very close to max. The induction changes were primarily to get rid of the grid heater since I had had two friends have the bolt melt off on the grid and ruin their #6 cylinder. I will recheck the Speedo and do some exact recordings of speed vs rpm to further refine my data. Thanks for the input.

 

[turretplug]

You know that your truck was geared right for perfect milage and pulling power right from the factory?
Even with the 35er it was just perfect.
4,56 may be right for a gasser that screams down the road with 6000rpm like my buddy's 2500 HEMI but for a Diesel that decision was the wrong one, sorry. You'll never get that milage back that you sacrificed with that gearing.

I know the Dodge engineers are far better than I am but I did take a larger mileage and towing performance hit when I decided to go with my larger tires. They have been on the truck for quite a few years and on long grades I would see near max EGTs as well as the transmissions doing a lot of shifting. Thanks for the input.

 

[turretplug]

I had 4:10s in my 04 pulling 20k and I never thought I needed more... in fact often wished I had the 3:73s..

I had the 3:73s originally and with the larger tires it did make a pretty big hit to mileage and towing performance since I live in the northwest and spend a fair amount of time camping in the hills as well as towing my horse trailer and other trailers in hill country. Appreciate the input and I will spend some time doing detailed recording of speeds and rpm’s to see exactly what is going on with my current setup.

 

[AH64ID]

I had the 3:73s originally and with the larger tires it did make a pretty big hit to mileage and towing performance since I live in the northwest and spend a fair amount of time camping in the hills as well as towing my horse trailer and other trailers in hill country. Appreciate the input and I will spend some time doing detailed recording of speeds and rpm’s to see exactly what is going on with my current setup.

Is the truck a DRW?

What tires are you running?

What are you running for a tuner? HO or SO?

 

[bcbender]

What tires are you running?

He said he was running a 35".. I dont know what the stock tire size is on a 16, but the stock OEM tire on my 2020 is 34.5" so I cannot imagine that impacting things greatly,..

I am confused about hitting the MAX Egts?? seems like dropping to 4th is not a bad thing IMHO, the truck should do what it needs, but I pull my 16k / 44' 5er up 10 mile 7% grades with stock 3:73 gears and she stays in 5th... no issues even at 70. My old 04 would run at the redline in direct (NV5600 5th gear / 4:10s) with zero issues and that was about 60ish, couldve run in 6th but didnt want to dump the trans..... My EGTs were never an issue on that truck and I was also running 34" tires, pulling over 16k.

 

[AH64ID]

He said he was running a 35".. I dont know what the stock tire size is on a 16, but the stock OEM tire on my 2020 is 34.5" so I cannot imagine that impacting things greatly,..

But what kind of 35? The type can make a huge impact on performance.

I am confused about hitting the MAX Egts?? seems like dropping to 4th is not a bad thing IMHO, the truck should do what it needs, but I pull my 16k / 44' 5er up 10 mile 7% grades with stock 3:73 gears and she stays in 5th... no issues even at 70. My old 04 would run at the redline in direct (NV5600 5th gear / 4:10s) with zero issues and that was about 60ish, couldve run in 6th but didnt want to dump the trans..... My EGTs were never an issue on that truck and I was also running 34" tires, pulling over 16k.

Yeah the EGT comment is why I’m wondering what tune he’s running… and that’s likely the issue over 35’s.

 

[turretplug]

Is the truck a DRW?

What tires are you running?

What are you running for a tuner? HO or SO?

 

[turretplug]

They are the newer Mickey Thompson’s that are very similar to BFG Mud Terrains. Aggressive pattern but a 50k tire with appropriate load rating for the work the truck does. Definitely has a much higher rolling resistance than a standard style tread pattern which I know I will simply have to live with since I like the style. I am not running any kind of tuner at all.

SRW with 68RFE.

 

[Ozymandias]

Why do you worry about EGTs when you have no tuner on it?
The EGTs will never go over the design limit of the Engine and its parts. No way.
You can floor that thing all day long without doing any harm.

 

[AH64ID]

So far all I’m getting is that you have an unrealistic expectation of your truck. Dropping 2 gears for grade in the PNW is normal with stock sized tires and 35’s won’t help that. Dropping 2 gears puts you in direct drive, and the appropriate gear for the grade when towing as overdrive reduces engine torque to the wheels from engine output torque. TH mode doesn’t change gear ratios, just shift patterns and even that’s designed to run lower gear more than higher gears. Some more recent model years can hold 5th, but the power output and gear difference adds up.

35’s just aren’t that much bigger than stock. 4.56’s is just a bit much, so you either got some really bad intel or advice. 4.56’s for 35’s is something that’s done in a Jeep with a small gas engine. Once you’re out of first gear the towing advantage to gearing starts to diminish. Gears are great for slow speed use, towing or off-road, but going that low for highway and interstate speed towing isn’t helping economy but I’ll bet it’s responsive.

The truck had 3.42’s from the factory, not 3.73’s. All 13-18 SRW’s had 3.42’s.

Without a tuner you don’t have to be concerned with EGT’s, let it run. It won’t hurt itself.

You have two very unlucky friends, the grid heater bolt failing is very very rare and easy to prevent with the jiggle test.

Drive it and enjoy it, because you’re where you’re at and even if you regeared to the proper gears for your tire size the mileage gains wouldn’t likely ever pay for the regear.

 

[kthaxton]

So far all I’m getting is that you have an unrealistic expectation of your truck. Dropping 2 gears for grade in the PNW is normal with stock sized tires and 35’s won’t help that. Dropping 6 gears puts you in direct drive, and the appropriate gear for the grade when towing as overdrive reduces engine torque to the wheels from engine output torque. TH mode doesn’t change gear ratios, just shift patterns and even that’s designed to run lower gear more than higher gears. Some more recent model years can hold 5th, but the power output and gear difference adds up.

35’s just aren’t that much bigger than stock. 4.56’s is just a bit much, so you either got some really bad intel or advice. 4.56’s for 35’s is something that’s done in a Jeep with a small gas engine. Once you’re out of first gear the towing advantage to gearing starts to diminish. Gears are great for slow speed use, towing or off-road, but going that low for highway and interstate speed towing isn’t helping economy but I’ll bet it’s responsive.

The truck had 3.42’s from the factory, not 3.73’s. All 13-18 SRW’s had 3.42’s.

Without a tuner you don’t have to be concerned with EGT’s, let it run. It won’t hurt itself.

You have two very unlucky friends, the grid heater bolt failing is very very rare and easy to prevent with the giggle test.

Drive it and enjoy it, because you’re where you’re at and even if you regeared to the proper gears for your tire size the mileage gains wouldn’t likely every pay for the regear.

This.
Except.....I prefer the jiggle test as opposed to the "giggle" test.

 

[AH64ID]

This.
Except.....I prefer the jiggle test as opposed to the "giggle" test.

lol, yeah it’s probably more effective

 

[kthaxton]

I do jiggle when I giggle however...like Santa.