Am I Crazy for Considering this 18 Dually

[Cummins12V98]

Guess you got a good one.

 

[cerberusiam]

What transmission, auto or manual? With 4.10's you will need some more tire to get better mpg, a 34 to 35 inch tire will help some. Monstir Mayhem wheels is a good solution for 20" rims that you can get multiple tires for. It will be spendy and rotation has to be dismount\mount tires.

Your mileage will vary based on driving style, speed, and terrain, there is no hard and fast rule. A tuner will help optimize that to a degree.

That is a good price on a very capable truck that has a lot of potential for heavy towing if needed. If you can deal with the reduced MPG and the increased costs on tires\wheels then do it.

 

[pwr2tow]

Guess you got a good one.

Going off of memory here.
1999 Ram Cummins DRW 48re - 16mpg
2005 Ram Cummins DRW nv5600 - 16-17 mpg
2006 Ram Cummins SRW 48re - 17-18mpg
2009 Ram Cummins SRW 68rfe 18-19mpg
2014 Ram ecodiesel 23-24mpg
2016 Ram Cummins SRW 68rfe 18-19mpg
2018 Ram Cummins DRW Aisin 18-19mpg.
All summer fuel reports. Winter can deduct 1-2mpg.

I do use a cell phone app to track mpg but after a few months of average always being +or- a couple tenths it's a waste of my time.

 

[pwr2tow]

Here's a liars photo for yah from my ecodiesel. I can guarantee the average was 23-24mpg.
The bottom picture is the total round trip which includes 13 miles of city driving. Notice the average mph? That's from slowing down for small towns and country stops at intersections. The exact same route I said about earlier. Been driving this exact same route for 38 years.

 

[pwr2tow]

My 2016 came with 3.42 gears, I swapped to 4.10 gears and actually gained a few tenths mpg on stock wheels and tires.

Now a stock 4.10 geared truck from factory is going to get what it is. I don't believe for one second putting on taller heavier tires is going to increase mpg. Not only is it 4 tires but 6 tires!!!

 

[HFolb23]

What transmission, auto or manual? With 4.10's you will need some more tire to get better mpg, a 34 to 35 inch tire will help some. Monstir Mayhem wheels is a good solution for 20" rims that you can get multiple tires for. It will be spendy and rotation has to be dismount\mount tires.

Your mileage will vary based on driving style, speed, and terrain, there is no hard and fast rule. A tuner will help optimize that to a degree.

That is a good price on a very capable truck that has a lot of potential for heavy towing if needed. If you can deal with the reduced MPG and the increased costs on tires\wheels then do it.

The 2018 is an automatic, 68rfe truck.

Can you explain needing a taller tire to get better fuel mileage with the 4.10 rear? I’m not doubting you, just don’t understand. My understanding is that the more rotating mass a tire has the less fuel mileage you should expect to get, however I don’t understand rear end ratios as well.

I have no interest in running aftermarket wheels, just increasing the tire size and using the stock wheels. I’d be looking at something in the 34in range, but skinny enough to stay on the stock wheels without having to worry about too much rubbing.

 

[AH64ID]

Not a lot of tire options but the 255/80R17 should fit the rears without a spacer.

Yes more rotating mass will take more power to turn, but if you can save enough fuel by dropping rpms then it can be a net gain on fuel. my 0.02 is that you won't see much of a net change with a tire size increase, even with 4.10's.

 

[Cummins12V98]

My 11 HO DRW 3.42’s basically same mileage as current 15 DRW 4.10’s towing or solo.

 

[Cummins2014]

Going off of memory here.
1999 Ram Cummins DRW 48re - 16mpg
2005 Ram Cummins DRW nv5600 - 16-17 mpg
2006 Ram Cummins SRW 48re - 17-18mpg
2009 Ram Cummins SRW 68rfe 18-19mpg
2014 Ram ecodiesel 23-24mpg
2016 Ram Cummins SRW 68rfe 18-19mpg
2018 Ram Cummins DRW Aisin 18-19mpg.
All summer fuel reports. Winter can deduct 1-2mpg.

I do use a cell phone app to track mpg but after a few months of average always being +or- a couple tenths it's a waste of my time.

That 2016 SWR 68RFE falls right in line with what my 2014 3500 Megacab gets. I have seen just over 21 hand calculated just once running empty. Most times right there at 18-19 running 70-75 mph.

 

[cerberusiam]

You won't get a 17" tire over 33" that will fit the rims or spacing. That is the problem with the 17" rims on the duals, not enough spacing to run a taller tire. With a 17" tire as you go taller you have to get wider to allow the tire to handle the weight.

Now, when go to 20 rims you can go taller with the tire and keep the section width narrower because the sidewalls are shorter. As for weight, the aftermarket rims are aluminum alloy compared to factory steel, that plus less sidewall and section width can equal less rotating mass depending on what you buy.

With 4.10 gears you have the extra leverage to get the mass rolling so you can upsize and actually gain efficiency, more leverage can mean less effort to get a heavier mass moving and keep it moving. Plus, dropping rpms never hurts unless it is so far it increases engine load. A little tuning in there won't hurt either. You have enough OD ratio to make it work.

The other aspect is ride quality, the 17's simply do not ride like a 20" tire. The 20's on aluminum alloy rims is hard to beat for all around performance.

 

[Cummins12V98]

As soon as you increase the diameter of the stock tire size you are making the gearing taller in reality and will have less pulling power.

 

[SnoKing]

As soon as you increase the diameter of the stock tire size you are making the gearing taller in reality and will have less pulling power.

I thought RAM duallies pulled great even with 3.42 gears? What would it take to turn 4.10's into 3.42's, 40" tires or larger?

 

[Cummins12V98]

I thought RAM duallies pulled great even with 3.42 gears? What would it take to turn 4.10's into 3.42's, 40" tires or larger?

I simply stated a fact. IF you want them to be more equal simply drop a gear as I have suggested in the past. You certainly can make a 4.10 truck a 3.42 truck by going with taller tires. I am not smart enough to give that specific info.

Anyone???

 

[Ozymandias]

There is no difference pulling into a drive through with a DRW because the mirrors on both trucks are the widest part.
No?

 

[Ozymandias]

I simply stated a fact. IF you want them to be more equal simply drop a gear as I have suggested in the past. You certainly can make a 4.10 truck a 3.42 truck by going with taller tires. I am not smart enough to give that specific info.

Anyone???

One point can not be talked away, with the 3.42 the steps between the gears are bigger.
So the 4.10 will gain speed faster, but at the end, yes, one can drive in 5th instead of 6th and call it a day.
Same with the EB, the 4.10 have 25% more retarding power at the same gear.

 

[AH64ID]

One point can not be talked away, with the 3.42 the steps between the gears are bigger.
So the 4.10 will gain speed faster, but at the end, yes, one can drive in 5th instead of 6th and call it a day.
Same with the EB, the 4.10 have 25% more retarding power at the same gear.

The steps between gears are not changed with gear ratio. The speed will be different, but the rpm change is identical.

 

[Ozymandias]

The steps between gears are not changed with gear ratio. The speed will be different, but the rpm change is identical.

View attachment 117999

Check again, the shift rpm is the same yes, but for each gear to shift the truck with 3.42 has to go average 4mph faster then the one with 4.10
First-second 4mph, second-third 8mph, third-forth 11mph, .....

 

[HFolb23]

The steps between gears are not changed with gear ratio. The speed will be different, but the rpm change is identical.

View attachment 117999

Do you know if these charts would be the same for the 68RFE trans?

Also not sure if I’m reading that right but does that chart say it won’t shift into 6th until 101 and 84? Is that kilometers per hour? My truck now with 3.42s shifts into 6th at like 55mph.

 

[AH64ID]

Check again, the shift rpm is the same yes, but for each gear to shift the truck with 3.42 has to go average 4mph faster then the one with 4.10
First-second 4mph, second-third 8mph, third-forth 11mph, .....

That doesn't change the gear steps, just the speed. Gear steps are based on engine rpms, or at least they are to me.

The speed increase is going to be the same percentage change at every shift too, it doesn't get wider as gears/speed increase.

For a given rpm/gear the 3.42 truck will always be going 19.8% faster... but the steps will remain the same.

Do you know if these charts would be the same for the 68RFE trans?

Also not sure if I’m reading that right but does that chart say it won’t shift into 6th until 101 and 84? Is that kilometers per hour? My truck now with 3.42s shifts into 6th at like 55mph.

The 68RFE does have some different gear ratios so it’s not exact.

That chart is also based on shifting at 2500 rpms. Depending on load/throttle your truck will almost always shift at lower rpms. So if you were to hold 5th until 2500 rpms you would be doing 101 mph, and drop into 6th at 2045 rpms...with a AS69RC

 

[SnoKing]

That doesn't change the gear steps, just the speed. Gear steps are based on engine rpms, or at least they are to me.

The speed increase is going to be the same percentage change at every shift too, it doesn't get wider as gears/speed increase.

For a given rpm/gear the 3.42 truck will always be going 19.8% faster... but the steps will remain the same.



The 68RFE does have some different gear ratios so it’s not exact.

That chart is also based on shifting at 2500 rpms. Depending on load/throttle your truck will almost always shift at lower rpms. So if you were to hold 5th until 2500 rpms you would be doing 101 mph, and drop into 6th at 2045 rpms...with a AS69RC

My Aisin in TH shifts at set speeds that are like 45 to 4th, 55 to 5th, 65 to 6th gear.