Diesel and Big Tires

[GARRIGA]

Since diesels get improved mileage over gas underload such as when pulling a trailer than is it fair to assume they also would have increased mileage with unsprung weight over gas? Going to 37 or even 42 would not be as big a drain on MPG as with a gas engine. Including adding beefier axles such as a Dana 60 swap and all the added weight that brings. Can see how this would help overlanders seeking extended range carrying all that gear.

Trying to determine all the benefits of waiting for The Holly Grail. I’ve waited this long.

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[GARRIGA]

Dumb question?

 

[JeepOn]

Its not a dumb question at all. Yes, diesel typically gets better mileage than a similarly equipped vehicles. And while I would advocate and say a diesel would do better in an overland situation where the Jeep would be loaded down with all the gear needed to transverse Siberia that’s not to say it can’t be done in a gas powered Jeep either. It really comes down to the efficiently of the diesel and the low end torque it provides for getting those bigger tires and heavier loads moving.

 

[GARRIGA]

I’m just assuming that diesels will deal better with unsprung weight such as heavier tires and another pro to consider if one is lifting their Jeep and putting on bigger shoes for both paved and unpaved roads.

 

[NFRs2000NYC]

This is where most people fail to understand the difference between a diesel and a gasser. Sure a gasser in stock form is close to a diesel, and will probably get close to the same mileage....but, load the Jeep with 1000lbs worth of armor and winches and lights, a fridge, 37" tires, etc etc etc and then tell me a gasser is the same. It's not even close, and the main reason why I want one. Also, a gasser will do 200-300 miles a tank, when a diesel can do 500-700 miles a tank....HUGE difference.

 

[JeepOn]

I could squeeze about 650 miles out of my last VW Jetta before the fuel light would come on, and that was with an average of about 45mpg. I can get over a 1,000 miles clocked onto my RAM before I need to refuel, but than again, it has a monster 55gal fuel tank strapped underneath it also. There are so many factors that one needs to take in to account when it comes to the rang and mileage. I diesel JL could possibly pull off a rang better than 500 miles yes, if your driving across Kansas in stock form. Loaded with gear and larger tires, maybe only if you kept it around 55mph, but this is just guess and Im basing that on a 27mpg estimate.

 

[NFRs2000NYC]

I could squeeze about 650 miles out of my last VW Jetta before the fuel light would come on, and that was with an average of about 45mpg. I can get over a 1,000 miles clocked onto my RAM before I need to refuel, but than again, it has a monster 55gal fuel tank strapped underneath it also. There are so many factors that one needs to take in to account when it comes to the rang and mileage. I diesel JL could possibly pull off a rang better than 500 miles yes, if your driving across Kansas in stock form. Loaded with gear and larger tires, maybe only if you kept it around 55mph, but this is just guess and Im basing that on a 27mpg estimate.

On ultra long highway rides, say like what I do, 2000 miles from NJ to Utah, at 75mph, it would be closer to 30 with the 8 speed. I regularly get 30+ with my dad's GC on long highway rides. Having said that, even at 27mpg, with a fully loaded rig, a gasser will barely stay above 15mpg, so it's a massive delta between the two. Having said that, fuel economy is not why I care about the diesel...it's the fact that it performs basically the same empty as it does loaded to the gills, where a gasser doesn't.

 

[JeepOn]

Okay, I see where your mind is going with this. I will tend to agree with you in all of this. I'm really hoping all these numbers being thrown around are even close to what real life numbers will be. I'm sure the diesel will do just fine fully loaded mated to that eight speed and still be able to pull decent numbers.

On the other hand of this, I didn't buy a Jeep because it got good fuel mileage, lets face it, its about as aerodynamic as a brick with wheels. The diesel should be the best of both worlds. Relativity good mileage in a vehicle that can go nearly anywhere.

 

[GARRIGA]

For me, this will also be my DD so more variables involved. Not going to change the fact it’s a box on wheels but perhaps make it more efficient and enjoyable box on wheels.

 

[pmcgeejr]

I agree with you both. Been holding off ordering my jl rubicon for seeing the diesel option and hoping its worth the wait. but whst you both are saying is my ideal jeep better mpg and im looking to put 40s or 42 and still will using for long travelings and will be my dd (which i don’t need to drive to work since i work at home)

 

[WXman]

Actually.....

The truth is that the more fuel efficient an engine is, the more sensitive it becomes to changes.

An engine that gets 30 MPGs in stock form with no load will lose significantly more fuel economy with large tires, armor, or when towing a trailer than an engine that normally sees 15-20 MPGs.

A good example would be found in the full size truck world. Those traditionally get bad fuel economy. But, you can load them up and they still get the same fuel economy.

From a driveability standpoint, the diesel will turn over large tires easier. But from a fuel economy standpoint, a diesel JL with huge tires and armor is going to get similar mileage to the gas counterparts.

 

[GARRIGA]

Since efficiency is dependent on wind resistance, overall weight and rpms then is the JL going to get better mpg because it’s lighter than full size trucks yet still overcoming being less aerodynamic or some other factor? My thought process is that how diesels operate is why underload they don’t lose as much efficiency and tried translating that to unsprung weight from larger tires.

Perhaps those with wrangler diesel conversions can chime in on mpg before and after putting on bigger shoes with everything else remaining the same. There’s also the impact of running gears appropriate to tire size but I’m still not clear on how that works with diesels.

At the end of the day. Trying to find every pro reason for going diesel. I’m trying to stack the odds in favor. Lol

 

[NFRs2000NYC]

Actually.....

The truth is that the more fuel efficient an engine is, the more sensitive it becomes to changes.

An engine that gets 30 MPGs in stock form with no load will lose significantly more fuel economy with large tires, armor, or when towing a trailer than an engine that normally sees 15-20 MPGs.

A good example would be found in the full size truck world. Those traditionally get bad fuel economy. But, you can load them up and they still get the same fuel economy.

From a driveability standpoint, the diesel will turn over large tires easier. But from a fuel economy standpoint, a diesel JL with huge tires and armor is going to get similar mileage to the gas counterparts.

This doesn't make sense. Of course the diesel will take a hit in fuel economy loaded with big tires and armor.....but the percentage of loss will be LESS than a gasser. A diesel just has more power to turn the tires and lug the weight, so you may drop from 30 to 25mpg, but a gasser with the same mods would go from 30 to 20, or even deep into the teens even.

 

[WXman]

This doesn't make sense. Of course the diesel will take a hit in fuel economy loaded with big tires and armor.....but the percentage of loss will be LESS than a gasser. A diesel just has more power to turn the tires and lug the weight, so you may drop from 30 to 25mpg, but a gasser with the same mods would go from 30 to 20, or even deep into the teens even.

I'm just reporting what I have personally experienced over the years with both gas and diesel Jeeps. The more fuel efficient a Jeep is, the more sensitive it becomes to changes.

Heck, even my current JL was this way. I just put on 285/75-17 tires and dropped from 22.5 to 19.0 MPGs. That's a 3.5 MPG hit. I've never in my life seen such a large hit on MPGs on my prior Jeeps and trucks with nothing but a tire swap, because those older vehicles weren't as fuel efficient to start with so they weren't as sensitive.

I think it comes down to the technology used today. The way they are getting these great numbers is with weight reduction and decreased friction. Well, those are the exact things that we're adding when we do tires, armor, suspension, etc. If you look at the Ram 1500, the EcoDiesel only has a rating of 3 MPG better than the Pentastar. That's a heavier vehicle, and once you start adding weight and resistance to the driveline, the diesel loses MPGs faster than the gas counterpart.

 

[Raylan Givens]

Obviously doing something that drops fuel economy by a certain percentage, use 10% for easy math, will cause a larger drop in mpg in the vehicle with the higher numbers. Using that 10% the vehicle with 20 mpg drops to 18, the vehicle with 30 drops to 27; the vehicle with 30 mpg loses 3 while the one with 20 loses 2.

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