More MPG confussion

[0duksgvn]

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?

Sponsored

 

[Lunentucker]

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

 

[0duksgvn]

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

that doesn't make sense to me seeing as I drove both in the same weekend/ temperature.

 

[Mr._Bill]

Was the computer adjusted for the larger tires?

 

[ShadowsPapa]

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?

Two different trucks, different weights, shapes and so on. The tires and gearing will matter. How much time it spends in each gear, the load on the engine in each gear and more.
It's way too complicated to try to explain here - you are not comparing the same trucks with the same gearing and the same tire size. So the mpg will vary - quite a bit.
The tires themselves will matter and no playing with pressure is going to get rid of a difference.
Tire width, tire sidewall and tread flex, tire weight.
You just have way too many variables coming into play.
Even if they were both Mojaves, if they had different tires it would matter.

The bottom line is - you'll have to go get a degree in engineering, do massive calculations on the drag of each vehicle (Mojave vs. Willys), the impact of tire rolling resistance, the final ratio (engine RPM at a given speed, and the load on that engine at that given speed) and more.

I bet if you used an app like JSCAN and watched the torque output on each Jeep at a given speed, you'd find a difference.

75 mph is also a horrible area for mph on these bricks on wheels. The wind resistance increases exponentially above about 60 so if there's more drag on one than the other, that effect will be exaggerated at 75.

Did the wind change at all between driving one vs. the other?
Did the ambient temperature change between driving one vs. the other?
Did you drive the EXACT same route with both?? If not, then forget you even tried to compare.

 

[ShadowsPapa]

that doesn't make sense to me seeing as I drove both in the same weekend/ temperature.

Winter blend is the GAS, not the air temperature, although that matters. Unless you gassed up both from the same pump at the same station and the air temperature was the same, and I don't mean 71 for one and 78 for the other - that's not the same - then you can't compare.
IF one had a full tank and the other was down to 1/4 you are talking a weight difference there, plus the weights of the trucks regardless of fuel weight.
Mojave is a heavier truck.

Winter blend gas is what's used in the winter per EPA regs - different states may have different rules and different timing for introduction to the public, but it makes a difference in mpg. So if one had a tank of gas from last month and you just filled the other with fresh gas that is winter blend, that will account for some of it.
but seriously, stop trying to find "the difference" because it's going to be many differences - two different trucks.

 

[0duksgvn]

I guess that's what my next question was, if the Willys just naturally get better MPGs than the Mojave because of weight/aerodynamics. We actually both just filled up from the same gas stations within 24hrs of each other, so I don't think that plays a huge role. Her tire size was corrected using the Tazer with actual size, not just 35" lol.
I fully understand there are many factors that could possibly play a factor in the results. but I was just looking at it from the simplistic pov that a lifted JT with 3.73s and 35s gets better than a stock vehicle. Since its pounded in everyone's head here and everywhere else that it just won't/can't. Again, Willys vs Mojave, I know. But the fact that it's that much different in MPGs is kinda crazy. Also, hers has 10k miles my Mojave has under 2,500 miles. Just to add that in case someone asks or adds that to the equation. lol

 

[ShadowsPapa]

I fully understand there are many factors that could possibly play a factor in the results. but I was just looking at it from the simplistic pov that a lifted JT with 3.73s and 35s gets better than a stock vehicle. Since its pounded in everyone's head here and everywhere else that it just won't/can't.

It's true - the bigger tires and lift will drop mpg - Then again, you are comparing a lighter truck to a Mojave. Stop - you aren't even comparing the same trucks.

Mojave is heavier, it's not shaped the same - the hood shape will matter.
In fact, running boards or steps can change mpg.

Although you said you adjusted with the tazer - I'd bet I can make it closer.......... you used "actual size" but I bet didn't use rolling circumference. I bet you didn't do a 20 mile run and compare the odometer to a GPS app on the phone. I'd bet they are still off a bit.

Now compare to my Overland, if it was still stock........I'd have blown away that 19/20 mpg of your Willys.
Even now, I do get decent mpg. It's down a lot from what it was bone stock, the tires, and short lift and extra weight mattered a lot, but here's what mine was doing recently -

 

[Badunit]

Did you check her odometer (and therefore the speedometer) for accuracy? I get out on an interstate and check against the mile markers. The more miles the better so the difference has time to stack up. That could account for a small bit of the difference.

Her gearing and tires put her at about 2300 in 7th at 75mph. If yours is downshifting from 8th (2150rpm) to 7th (2700rpm) on every little hill while hers is sticking 7th (2300 rpm) the whole time, that might make a difference, too.

But, as has been pointed out already, there are way too many variables.

 

[0duksgvn]

It's true - the bigger tires and lift will drop mpg - Then again, you are comparing a lighter truck to a Mojave. Stop - you aren't even comparing the same trucks.

Mojave is heavier, it's not shaped the same - the hood shape will matter.
In fact, running boards or steps can change mpg.

Although you said you adjusted with the tazer - I'd bet I can make it closer.......... you used "actual size" but I bet didn't use rolling circumference. I bet you didn't do a 20 mile run and compare the odometer to a GPS app on the phone. I'd bet they are still off a bit.

Now compare to my Overland, if it was still stock........I'd have blown away that 19/20 mpg of your Willys.
Even now, I do get decent mpg. It's down a lot from what it was bone stock, the tires, and short lift and extra weight mattered a lot, but here's what mine was doing recently -

the only thing I've checked the MPH against is the speed limit digital tattle tale devices they put out, and it was spot on multiple times. (Btw, I'm pretty sure i got the highest score so far lol.) I guess I wasn't aware of the mpg difference between models. End of the day they all suck on gas. My 18 5.3L Tahoe with DOD tuned out got waaaay better mpgs. lol I appreciate your guy's input on this btw. Really left me scratching my head on this.

 

[Uparms]

2023 Sport MaxTow, 4.10s auto, 245/75/17 ---- 20.3 right now, highway and around town. 3300 miles.
2020 Sport, Max Tow, Auto 4.10s, 35x12.5, 17, 2 inch mopar lift. 17 around town and 19/20 on the big highway.

 

[Sailingmat]

ShadowsPapa is absolutely correct. However, just get a diesel
My 2022 Rubicon diesel on 38's with stock gearing, I average 21 mpg during the summer on my 55-mile one way commute. My prior Gladiator 3.6, built the same way, averaged 16 on my commute. Take off 3 to 4 mpg for the diesel and 2 to 3 for the gas during the winter (8 months up here).

 

[ShadowsPapa]

but I was just looking at it from the simplistic pov that a lifted JT with 3.73s and 35s gets better than a stock vehicle.

My bet - that Willys would get 21-22 once it was broke in (7,000-10,000 miles) if it was all stock, stock tires and wheels and no lift and stock bumper.

the only thing I've checked the MPH against is the speed limit digital tattle tale devices they put out, and it was spot on multiple times.

Still not ideal since your speedometer and those radar signs round numbers.
Odo is the best way - over several miles.
You can still be about 1 mph off when you compare things by speedometer.

However, just get a diesel

That's cheating - they don't care much what tires are on it or if it's a 6% grade - they'll still idle up hill in high gear.

 

[Badunit]

ShadowsPapa is absolutely correct. However, just get a diesel
My 2022 Rubicon diesel on 38's with stock gearing, I average 21 mpg during the summer on my 55-mile one way commute. My prior Gladiator 3.6, built the same way, averaged 16 on my commute. Take off 3 to 4 mpg for the diesel and 2 to 3 for the gas during the winter (8 months up here).

Those two mpgs equate almost exactly in $/mile using the "average" gas and diesel prices around here, though I've not seen prices as low as the so-called "averages". But diesel torque is awesome.

Gas: ($3.29/gal)/(16 mi/ga) = $0.2056/mi
Diesel: ($4.28/gal)/(21 mi/ga) = $0.2038/mi

I miss the days when diesel was cheaper than regular. The break even point on cost was so low. Now there is no break even point. You buy one because you want/need the torque or just love the sound of a diesel as it tractors up hills.

Sponsored