Milage not what I expected

[Dilly’S Willy]

I forget the rule of thumb, but it's something like for every 200# it costs 2-4% mpg.

Bigger, heavier, chunkier tires drop mpgs.
Taller, heavier vehicles drop mpgs.
Towing drops mpgs.

But we already knew this going in - just looking at a Gladiator or Wrangler know it's not the most aerodynamic thing on the market.

We call this Power/Weight Ratio.

Added weight with same power means slower acceleration. That's just static weight. For rotating mass, it's even more harsh: Every 5lbs of rotating mass = 20lbs of static mass. So those bigger/meatier tires that now weigh 60lbs compared to the Sport with 35lbs tires, means you've essentially added 240lbs that your truck now must move too.

Rotating mass isn't limits to tires, but also wheels, axles, R&P, differentials/lockers, brake rotors, etc. Those HD chromoly axles, yup more weight.

The aero drag is another factor, but with a speed limited below 100mph, it's mostly irrelevant. But for funzies: if it takes 10sec for a vehicle with 100hp to go 0-60, it will take 200hp to make the same vehicle go from 60-120 in 10sec (not factoring drag coefficient) and 400hp to go from 120-180 in 10sec. Learned in motorcycle racing where we reach 180+ often.

Making more power also uses more fuel. But if you're buying a truck for mpg, go buy a car with a pickup bed. Their modern ABS-based AWD will do most of what you want, other than low range crawling. Man remember the Brat? Best of both worlds for its time.

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[MPMB]

We call this Power/Weight Ratio.

Added weight with same power means slower acceleration. That's just static weight. For rotating mass, it's even more harsh: Every 5lbs of rotating mass = 20lbs of static mass. So those bigger/meatier tires that now weigh 60lbs compared to the Sport with 35lbs tires, means you've essentially added 240lbs that your truck now must move too.

Rotating mass isn't limits to tires, but also wheels, axles, R&P, differentials/lockers, brake rotors, etc. Those HD chromoly axles, yup more weight.

The aero drag is another factor, but with a speed limited below 100mph, it's mostly irrelevant. But for funzies: if it takes 10sec for a vehicle with 100hp to go 0-60, it will take 200hp to make the same vehicle go from 60-120 in 10sec (not factoring drag coefficient) and 400hp to go from 120-180 in 10sec. Learned in motorcycle racing where we reach 180+ often.

Making more power also uses more fuel. But if you're buying a truck for mpg, go buy a car with a pickup bed. Their modern ABS-based AWD will do most of what you want, other than low range crawling. Man remember the Brat? Best of both worlds for its time.

Yup. Parasitic drag. All that makes a difference.

And correction on aerodynamic drag - anything over 30mph matters (it's actually slightly less, but it's easier to say 30mph). Spent 16 years building racecars.

Our 2700# car with 415hp ran against 2900# cars with 575-600hp on the same tires. Rookie driver, first time at the track, first long race (125laps), finished 3rd. It was comical after ~40 laps how fast the lighter cars went through the corners.

 

[JTGuy]

Jeep did the windshield and grill and 8 speed trans and FAD all for better MPG. The VVL and VVT are also for MPG. LOL and the MPG still sucks.

 

[Flanders]

For rotating mass, it's even more harsh: Every 5lbs of rotating mass = 20lbs of static mass.

This myth gets repeated a lot. Here it's a factor of 4. I've seen worse.

The energy in the rotational component is less than that of the translational component.

It takes less than twice as much energy [power, torque, force transverse to the tread, or whatever real men care about] to accelerate the wheel on the axle as it would if the wheel were in the bed of the truck.

 

[Stan H]

This myth gets repeated a lot. Here it's a factor of 4. I've seen worse.

The energy in the rotational component is less than that of the translational component.

It takes less than twice as much energy [power, torque, force transverse to the tread, or whatever real men care about] to accelerate the wheel on the axle as it would if the wheel were in the bed of the truck.

Laymen terms please kidding .. wow now we are breaking out the dictionary

 

[Dilly’S Willy]

This myth gets repeated a lot. Here it's a factor of 4. I've seen worse.

The energy in the rotational component is less than that of the translational component.

It takes less than twice as much energy [power, torque, force transverse to the tread, or whatever real men care about] to accelerate the wheel on the axle as it would if the wheel were in the bed of the truck.

*Homer's voice: Nobody cares what YOU think, FLANDERS! (Kidding, unless you don't like the simpsons )

It's common knowledge to keep rotational weight down before reducing static weight, hence CF wheels vs alloy on motorcycles, or lighter flywheels to increase the rate the rpms increase, or smaller wheels and larger sidewalls in drag racing. It's not just about acceleration, but also the energy required from the engine to turn that added weight. The same reason why using a supercharger is (usually) less efficient than a properly sized turbo for forced induction, the engine now has to use the same power to spin the SC, vs exhaust gases you already create.

I'd still rather not need 400hp to rotate my (2x heavier) wheels/tires the same rate as it does stock (with your factor of 2). Yes THIS was rough math, not exact.

Jeep did the windshield and grill and 8 speed trans and FAD all for better MPG. The VVL and VVT are also for MPG.

They did it for emissions. Nothing they do is for mpg, not primarily though that's a huge factor.

NOTE: Most people have ZERO clue about what actually goes on regarding emissions standards, especially in the last decade. I am still getting caught up as I need to be able to comply with these requirements in my business since we're designing new vehicles for CARB compliance. And holy F&^% are these karens/politicians getting in over their heads.

 

[Flanders]

Laymen terms please kidding .. wow now we are breaking out the dictionary

A rolling wheel behaves as if its mass were multiplied by some factor. The multiple is less than 2. It would be exactly 2 if all of the mass were on the tread.

When you put heavier tires on your Jeep, it's safe to assume most of the incremental mass is near the tread, so go ahead and double it. If you add 25 lbs on each corner plus a spare, that's like adding 225 lbs of non-rotating mass.

This only applies to acceleration and braking. For everything else, use the actual weight of the wheel.

 

[Flanders]

Kinetic energy is proportional to mass and the square of speed. E equals one-half em-vee-squared.

The fastest moving point on a rolling wheel is the topmost, at twice the speed of the vehicle. Its opposite point in contact with road has speed zero - if it doesn't then it's in a skid. The mean square speed of the two points is twice the speed of the vehicle squared.

The last statement is true for any pair of antipodal points on the tread. This is why the mass on the tread gets counted twice in the energy formula.

Closer to the axis of rotation, speeds are lower and the contribution is less than 2.

 

[cb4017]

My 3 month old stock JTM is averaging around 16 mpg. This is tracked with Fuelly. If I remove the fills after hauling my 3,500 pound r-pod it's closer to 17.5 mpg. I suspect that will improve 1-2 mpg once they stop winter blend gas.

I've found it actually does better around town than when I'm pushing air on the freeway. Freeway driving I try to limit speeds to around 75 mph.

 

[Flanders]

@Dilly’S Willy

 

[FLY-DOG]

I recently traded a 22 grand Cherokee overland with a v6 penstar engine and replaced it with a 24 gladiator with the same motor. My question is this I was consistently getting between 18 and 20 mpg in the Cherokee but the new jeep seems to be much lower, 14 to 16. The rug has 10,000 on it now.should I be getting better mpg then that? For clarification it's a Rubicon on 33's with 4:10s and automatic

I recently traded a 22 grand Cherokee overland with a v6 penstar engine and replaced it with a 24 gladiator with the same motor. My question is this I was consistently getting between 18 and 20 mpg in the Cherokee but the new jeep seems to be much lower, 14 to 16. The rug has 10,000 on it now.should I be getting better mpg then that? For clarification it's a Rubicon on 33's with 4:10s and automatic

That's about right for everyday around town driving. You should get 17 - 19, maybe even 20 MPG average on the highway.

 

[Brucewillys]

I recently traded a 22 grand Cherokee overland with a v6 penstar engine and replaced it with a 24 gladiator with the same motor. My question is this I was consistently getting between 18 and 20 mpg in the Cherokee but the new jeep seems to be much lower, 14 to 16. The rug has 10,000 on it now.should I be getting better mpg then that? For clarification it's a Rubicon on 33's with 4:10s and automatic

Driving a 2021 gladiator Willys sport with the same 3.6. with 37" tires and 3:73 gears I average 19mpg for mostly work driving. My drive is around 40-50 mph the whole way. I rarely drive highway if I do the mpg drops. My super chips made a big difference in mpg and shift points. Honestly I pay attention out of curiosity, I love my Jeep and I live by smiles per gallon. I doubt there's anything wrong with your Rubi, they just love to drink.

 

[Nwjeepguy]

Driving a 2021 gladiator Willys sport with the same 3.6. with 37" tires and 3:73 gears I average 19mpg for mostly work driving. My drive is around 40-50 mph the whole way. I rarely drive highway if I do the mpg drops. My super chips made a big difference in mpg and shift points. Honestly I pay attention out of curiosity, I love my Jeep and I live by smiles per gallon. I doubt there's anything wrong with your Rubi, they just love to drink.

Thanks for your input. I would like to know some more about the super chip your running. I've been considering a tazer, can to provide me with some feed back?

 

[Brucewillys]

Thanks for your input. I would like to know some more about the super chip your running. I've been considering a tazer, can to provide me with some feed back?

I'm running the superchips flashcal +. I tried procal snap and it was horrible. Returned that after multiple failed pairing attempts and tried the flashcal. It has been great, you can set the tire size manually or have GPS do it for you. It uses an app for the settings instead of trying to navigate through the radio. When I switched from 34's to 37's I immediately noticed shift point issues, and annoying speedometer miscalculation. The flashcal fixed all that and more. I really like the start/stop and TCS memory. Surprisingly I enjoy the rear camera activation with blinkers also. Never tried a tazer but when my "basic" radio struggled with the procal snap I wanted something that did not rely on the radio. The superchips flashcal + seemed to be the best option. I doubt I'll be keep the Mopar radio forever anyway. Good luck! Pic because I have an unhealthy addiction to my jeep.

 

[Nwjeepguy]

I'm running the superchips flashcal +. I tried procal snap and it was horrible. Returned that after multiple failed pairing attempts and tried the flashcal. It has been great, you can set the tire size manually or have GPS do it for you. It uses an app for the settings instead of trying to navigate through the radio. When I switched from 34's to 37's I immediately noticed shift point issues, and annoying speedometer miscalculation. The flashcal fixed all that and more. I really like the start/stop and TCS memory. Surprisingly I enjoy the rear camera activation with blinkers also. Never tried a tazer but when my "basic" radio struggled with the procal snap I wanted something that did not rely on the radio. The superchips flashcal + seemed to be the best option. I doubt I'll be keep the Mopar radio forever anyway. Good luck! Pic because I have an unhealthy addiction to my jeep.

Thanks for the feedback, rig looks great with the 37s I'm going with 36s and just ordered a 2.5 lift , going to stay with the 4:10s for now and get a feel for it. We both be ave the same color too

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