More MPG confussion

[Sailingmat]

The main reason for our decision to trade up to a diesel instead of the 3.6-liter gas; a 3200 lbs. Tab 400 travel trailer. The truck literally doesn't know it's back there. However, the gas 3.6 gasser is a great engine, I loved it! Don't get too caught up in MPG's, that's not why any of us purchased a Gladiator.

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[Volt0]

Fwiw, the tire/wheel combo on my wife’s HA is about 30lbs lighter per corner than my JTM. Also hers is a highway tread vs my AT, she’s routinely 2 mpgs better than mine, and more peppy onroad. This is going to sound strange, but I honestly don’t feel like my 21 JTM was broke in until it had 35k on it ( and maybe some satisfaction campaigns).

 

[sharpsicle]

There's a lot to consider here:

• Age of the engine/drivetrain
• Miles on the engine/drivetrain
• Weight of the vehicle
• Wheelbase of the vehicle
• Gear ratios
• Road being driven on (quality, material, grade, etc.)
• Maintenance status of the vehicle
• Tires (including size, tread, weight, etc.)
• Blend of gas used
• Traffic pattern around the vehicle
• Presence of head/tail winds
• Presence of installed exterior accessories
• Elevation
• Ambient air temperature (yes, this impacts it too)
• Inaccuracies in the instant MPG display

I'm sure there are more.

All of these factors compound and combine. Nobody truly can quantify and understand each variable. Some are easier to control than others, but there's always a difference somewhere. You'll drive yourself nuts trying to figure out where each MPG is going, especially on a flying brick like these at 75mph. A sneeze from a gnat at 75mph will affect your MPG.

 

[TheRealStreetcommander]

Tire rolling resistance. It's never been popular to measure in the US, but many European testing outfits will test and publish it. The delta in rolling resistance between identical tire sizes from 20 different manufacturers can be 20%. That could easily create the variations you are seeing.

Our all factor Willys 3.6ZF 3.73LS can achieve ~22-23MPG hand-calc'd at 75-80MPH on highway, summer. 42-44psi tire pressure.

Theres legitimate maths behind why hyper-milers run pizza cutters.

 

[AmosMoses]

I average about 1-2 mpg less with a 21 rubi than I did on my 20 sport. Same engine/trans, suspension, wheels and tires, side steps, tonneau cover etc. The rubi does have 4.11 gears and steel front and rear bumper though.

 

[MattKay]

How are people driving their rubis to get good gas mileage in the city? I’m seeing 14 mpg. Mine is used with 80k. Any tips would be greatly appreciated! Id love to see 17-18 avg tho.

 

[Gvsukids]

I guess that's what my next question was, if the Willys just naturally get better MPGs than the Mojave because of weight/aerodynamics.

And gearing.

The main reason for our decision to trade up to a diesel instead of the 3.6-liter gas; a 3200 lbs. Tab 400 travel trailer. The truck literally doesn't know it's back there. However, the gas 3.6 gasser is a great engine, I loved it! Don't get too caught up in MPG's, that's not why any of us purchased a Gladiator.

Did you tow the trailer with the gas engine first?

How are people driving their rubis to get good gas mileage in the city? I’m seeing 14 mpg. Mine is used with 80k. Any tips would be greatly appreciated! Id love to see 17-18 avg tho.

It's about the speed in which they are driving. Also stock will do better than modified.

 

[MattKay]

And gearing.


Did you tow the trailer with the gas engine first?


It's about the speed in which they are driving. Also stock will do better than modified.

Does speed matter - I was under the impression that rpm’s mattered more. I honestly don’t know. Im experimenting with manually shifting the auto to like gear 6 in town to keep rpm’s at like 1500. Also the red lights and stop signs kill any gains lol. I am wondering too if getting rid of the falkens and doing a more street friendly AT would help any? Like everyone says - it is what it is. Im just looking for “if you were set up like this with the stock 4.10 gears you’d be at the best condition you could be”

 

[BAT]

Give yourself a break and take some advice don't go any further in trying to figure it out. I can already tell you from experience its a rabbit hole you would be going down. Ever since 2020 when I got mine I have just been shaking my head and trying to figure out how people driving basically the same truck (Maybe a JT Rubicon or other) but theirs is on monster tires and all kinds of gear, etc are able to get way better than me in my JT Max Tow with nothing but Rubicon Take off Tires and rims.

 

[sharpsicle]

Does speed matter - I was under the impression that rpm’s mattered more. I honestly don’t know. Im experimenting with manually shifting the auto to like gear 6 in town to keep rpm’s at like 1500. Also the red lights and stop signs kill any gains lol. I am wondering too if getting rid of the falkens and doing a more street friendly AT would help any? Like everyone says - it is what it is. Im just looking for “if you were set up like this with the stock 4.10 gears you’d be at the best condition you could be”

Speed matters a LOT.

More speed = more drag.

More drag = more resistance.

More resistance requires more energy to overcome.

Energy required to move = MPG.

 

[Ryan...]

Winter blend will do that, drop MPG.
Mine just went from 19 to 17.

Yep, I just dropped from 18.2 to 16.3 basically overnight. Same commute (90 miles of straight highway every day), same everything. Oh well, just part of living where it gets cold

 

[ShadowsPapa]

Don't get too caught up in MPG's, that's not why any of us purchased a Gladiator.

Welllll.........
I went that way IN PART, not primary reason, but a fair part, because it trounced the mpg of the Silverado I used to have, and beat out my WJ and some other vehicles I had.
Primary, no - but a player, definitely on the list. I avoided another full size truck for many reasons - one of them mpg.

Does speed matter - I was under the impression that rpm’s mattered more. I honestly don’t know.

RPM is only a factory combined with other criteria. Speed matters due to drag. Wind resistance increases exponentially (look it up) and the reason we were limited to 55 mph national speed limits decades ago was due to the fact that science proved that anything over about 55-60 drastically reduced mpg. Of course the shape, size and weight matter, but take any given vehicle and keep increasing mph and once you hit that magic number, mpg drops fast.
RPM is only part of it and that's where the engine design, tuning, and too many other factors to discuss get into the mix. You can actually get better mpg with some engines at higher rpm, if the load balanced with heat rejection, hp and torque curves and other things are at their best at those higher RPM. I find I do just as well with RPM up in the mid-20s while towing as compared to trying to keep it at a lower RPM - working it harder, it's less efficient, etc. When not towing, it's the other way around with my particular JT
In the past I've seen cases where guys would take a I6 engine out of a mid to full size car and drop in a V8 and get better mpg. Then there are times that doesn't happen.
It's way too complex to cover in a few posts in a forum.
I went to college for some of this stuff and I still stumble and stub my toe now and then.

 

[Gvsukids]

I am wondering too if getting rid of the falkens and doing a more street friendly AT would help any? Like everyone says - it is what it is. Im just looking for “if you were set up like this with the stock 4.10 gears you’d be at the best condition you could be”

Yes. Weight matters, so a lighter tire helps mpg. A smaller tire helps too.

 

[Stan H]

So, to start this off, I have a 21 Mojave completely stock, the wife has a 22 Willys AEV 2.5" lift and 35s on fuel wheels with stock 3.73 gears (not seeing 8th gear continuously of course). I had the opportunity to jump in the driver's seat of both this weekend and noticed at 75mph/cruise control on both and noticed mine averaging 16mph while hers was averaging 19/20mph. Her tires are set at 32psi, and I have mine set at factory door specs of 37psi (I've also played with different psi's without better results on my Mojave). For the life of me I can't make this make sense to me. Can someone with a bigger brain than mine explain this to me?

I am going with..
An object in motion tends to stay in motion.
You said both at 75 mph. Once the big wheel get rolling at 75 they will tend to roll on better and will also take more to stop.
That's my theory on it anywho.

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