What Most Hurts MPGs: Weight, Diameter or Width

[Yawnie'sPapa]

When I changed from the stock H/Ts on my Gladiator Overland to A/T tires, I saw a decrease in mph (taken long term) of almost 2 mpg.
Then I added steel bumper and winch. That made it not only heavier but less aerodynamic (I know, 10 demerits for mentioning that word with a Jeep) - and I lost more mpg.
I started doing 21, even 22 pretty easily. I'm now lucky to get into the 19s although in the flats of Florida last fall I saw 20-21 again.
WIND is a huge factor on these, so on some days it's going to be the changes to make like letting air hit the fronts of the front tires, removing the air dam below the bumper, changing bumper SHAPE, etc. - other days, weight will matter more.
Once I had the tires changed and the steel bumper and winch, other changes like adding a 2" receiver and the heavy mounting brackets and mounting bar for a snow plow - it didn't matter much.

It's going to impact different Jeeps differently - a 2.0 vs a 3.6 vs. a 3.0............ one guy may have more problem with tire's rolling resistance and weight and other guy have more change with a bumper.

There's no magic formula.
I've made a lot of changes to two different Jeeps - including taking stuff back off little by little so I could trade one for another. Results were interesting and a bit contrary to what the "superior intelligence" of the internet says.

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[roaniecowpony]

Weight of the tire is way down the list of effects on mileage, IMO. If you could majically make a tire that is half again as heavy, yet the same diameter and tread, as well as rolling resistance, you'd likely barely be able to detect any mileage differences. Certainly not at sustained highway speeds speeds.

Which brings up "rolling resistance". Something rarely discussed when talking about tires and their effect on mileage. I think we all can agree that, all things being equal, additional width would increase rolling resistance. But, tread types have a big impact on rolling resistance too. Going from a mild street pattern to a more aggressive pattern has a significant impact on rolling resistance. The more aggressive the pattern, the more rolling resistance. Add in extra width, larger diameter, lower pressures for ride comfort, raised stance for tire and obstacle clearance, tires poking out of the fenders, narrow bumpers exposing the front tires and wheelwells to the slipstream, and yeah even the weight, and it all adds up.

From a practical standpoint, it's hard to put your finger on one characteristic that is the most influential on mileage. For example, if you increase diameter drastically, but keep a mild tread, narrow width, light weight, and inflated to the same pressures, the effect on mileage might be small, certainly smaller than if you went to a tall mud tire, that had half again more width, and you drop the pressure 10 psi.

 

[roaniecowpony]

If you want to see the effects of tread width and tread style, ride a mountain bike then ride a street bike with the same diameter tires. It gets pretty clear that those two characteristics are big swingers.

 

[five9dak]

Yes, my prior car was a 575 hp twin turbo V8 X6M that averaged around 16.5 MPG and I never gave the mileage a second thought. But with this 392 I’m hitting the pump every 4 days. It’s ridiculous.

In years past I’ve also had this same 6.4 engine in 4 chargers and challengers and once in a Durango and it was never this bad.

The jeep has more than double the frontal area of those cars, and worse C/D.

 

[ohthatguy]

Based on the limited data available, it appears that I improved my consumption from 4 days on a tank to 4.5 days per tank.

 

[3TV]

Why all this concern over fuel mileage on a 392? If you can afford to buy a 392 (and not just make the payments), then the cost of fuel is such a tiny portion of your yearly expenses that it doesn't even matter. Housing cost, eating at restaurants, and especially taxes for someone in that income bracket, are goiing to make fuel cost a very minor concern.

I get the impression you are checking fuel mileage with every drive, and sometimes several times per day. I've owned my 392 for nine months now, and I have no idea what fuel mileage it gets. I've never checked, not even with the dash computer. I don't really care, because it is the funnest driving Jeep I've owned in 48 years of owning Jeeps. I certainly can't tell you how much effect the suspension lift made, or changing to 37" tires, or adding weight with a winch, air compressor, and recovery gear.

The limited fuel range is a nuicance, I'll give you that much.

It doesn't sound like you're too happy with your 392. Hopefully it works out for you.

 

[ohthatguy]

Why all this concern over fuel mileage on a 392? If you can afford to buy a 392 (and not just make the payments), then the cost of fuel is such a tiny portion of your yearly expenses that it doesn't even matter. Housing cost, eating at restaurants, and especially taxes for someone in that income bracket, are goiing to make fuel cost a very minor concern.

I get the impression you are checking fuel mileage with every drive, and sometimes several times per day. I've owned my 392 for nine months now, and I have no idea what fuel mileage it gets. I've never checked, not even with the dash computer. I don't really care, because it is the funnest driving Jeep I've owned in 48 years of owning Jeeps. I certainly can't tell you how much effect the suspension lift made, or changing to 37" tires, or adding weight with a winch, air compressor, and recovery gear.

The limited fuel range is a nuicance, I'll give you that much.

It doesn't sound like you're too happy with your 392. Hopefully it works out for you.

Yeah, every vehicle I’ve owned offered a compromise of utility and fun weighed against its limitations and costs. I probably do glean less from this platform than most.

It isn’t because it’s not fun. This thing makes glorious noises. But there’s an old saying that comparison is the thief of joy. That likely applies in my case because I’ve been lucky enough to enjoy some pretty special vehicles.

Fuel economy has thankfully never been something I had to give much thought to over the years. The fact that it’s on my mind now probably is an indicator that the 392 is delivering too much compromise in various areas vs the enjoyment it delivers..

But given the percentage of the global population that wakes up to a dirt floor, I count myself lucky to have the opportunity to experience it.

 

[TheBirdie72]

Based on the limited data available, it appears that I improved my consumption from 4 days on a tank to 4.5 days per tank.

I think you hit the nail on the head here. Your weight is definitely a factor and is directly related to your consumption. if you went from spending 4 days a week at the donut shop to 4.5 days a week at the donut shop, then your weight will definitely increase!

Try staying away from the donut shop for a week and you’ll see consumption decrease dramatically as well.

Driver/passenger weight affects MPGs, too! ??

 

[GMONEY]

Yes, my prior car was a 575 hp twin turbo V8 X6M that averaged around 16.5 MPG and I never gave the mileage a second thought. But with this 392 I’m hitting the pump every 4 days. It’s ridiculous.

In years past I’ve also had this same 6.4 engine in 4 chargers and challengers and once in a Durango and it was never this bad.

You are driving a brick on wheels. Nothing you do is going to overcome the shit aerodynamics of a brick to give you truly meaningful gains.

Stay out of the throttle for the sound, coat to a stop. Stay under 65 mph that's good you'll get better gas mileage.

Also like mentioned you need to recalibrate everytime you change your size to truly know what you're at.

 

[GMONEY]

If you want to see the effects of tread width and tread style, ride a mountain bike then ride a street bike with the same diameter tires. It gets pretty clear that those two characteristics are big swingers.

Mountain bikes and road bikes are geared completely differently. Now move the tires to the same frame/ gearing and yes you'll see a difference but not as dramatic as comparing a mountain bike at up with a road bike set up.

 

[TheBirdie72]

Mountain bikes and road bikes are geared completely differently. Now move the tires to the same frame/ gearing and yes you'll see a difference but not as dramatic as comparing a mountain bike at up with a road bike set up.

But an overweight fat guy on a bike is still gonna get worse mileage than a skinny in-shape one. I stand by my earlier point about donuts. ?

 

[roaniecowpony]

Mountain bikes and road bikes are geared completely differently. Now move the tires to the same frame/ gearing and yes you'll see a difference but not as dramatic as comparing a mountain bike at up with a road bike set up.

They both have levers to change gears. You'll feel the difference regardless, just coasting.

 

[roaniecowpony]

You are driving a brick on wheels. Nothing you do is going to overcome the shit aerodynamics of a brick to give you truly meaningful gains.

Stay out of the throttle for the sound, coat to a stop. Stay under 65 mph that's good you'll get better gas mileage.

Also like mentioned you need to recalibrate everytime you change your size to truly know what you're at.

I had a career in aviation. Whenever I see a vehicle (plane, car, truck, etc,) with high drag, I see big opportunity for reducing drag.

If you take a plane like the 787 Dreamliner, there is very little opportunity for aerodynamic improvements.

I owned an aerobatic biplane that had tremendous (coefficient of) drag in comparison. There were many easy things I did that greatly improved aerodynamics. I increased the top speed of that plane by double digits and reduced cruise fuel consumption significantly.

With a Jeep, it likewise has a lot of low hanging fruit. A lot more than a new modern sedan or sportscar. Also, with a vehicle that gets low fuel economy, driving the same miles per year, an X% gain in fuel economy equates to more $$ per year than for the high efficiency car.

In other words, higher drag vehicles have higher gains in $$ for drag reducing efforts.;

 

[Antonio]

My foot is the biggest contributor to effect the MPG ??? honestly if you purchased a jeep and you’re worried about MPG you’re either not enjoying your jeep to its full potential or you purchased the wrong vehicle! ?

 

[TheBirdie72]

I had a career in aviation. Whenever I see a vehicle (plane, car, truck, etc,) with high drag, I see big opportunity for reducing drag.

If you take a plane like the 787 Dreamliner, there is very little opportunity for aerodynamic improvements.

I owned an aerobatic biplane that had tremendous drag in comparison. There were many easy things I did that greatly improved aerodynamics. I increased the top speed of that plane by double digits and reduced cruise fuel consumption significantly.

With a Jeep, it likewise has a lot of low hanging fruit. A lot more than a new modern sedan or sportscar. Also, with a vehicle that gets low fuel economy, driving the same miles per year, an X% gain in fuel economy equates to more $$ per year than for the high efficiency car.

In other words, higher drag vehicles have higher gains in $$ for drag reducing efforts.;

Also true. This is why a cow is more aerodynamic than a Jeep.

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