Generally speaking, the differences are going to show up more in HOW you drive.
If you were to put the different configurations on a roller and let them run in cruise control at the same speed, you might see a difference in MPG.
You can drive the same set up hard and softly and get two different MPG rates.
Next, wheel weight vs. what will you be carrying in the car? How much do passengers weigh? Do you drive with a full tank of gas or a quarter tank? Anything to increase drag like roof racks?
A total of 25 pounds isn't something you're likely going to notice.
AT tires vs. street tires will reduce mileage in itself, even if they are the same weight just because of the tread design.
Another option is to get a set of wheels with tires for street driving and another set just for off-roading.

 

I'm really doing a lot of searching and attempting to figure out direction on wheels and tires.
2023 Outback Onyx (Non-XT). I love this car and love the decent mileage I get with it. I know that compromise is something I am going to have to deal with.
I have been looking a lot at tire/wheels. I knw what tire I want, the Falcon Wildpeak AT Trail. These tires are about 5lbs over stock. I want 17in tires, I do plan to do a fair bit of off road driving. Full skid plates arriving next week.
The wheels I am looking at range from 17.5lbs up to 28lbs or more. Stock seems to be about 25lbs. I know that with the added 5lbs being at the tire it has more effect than being at the wheel. (Like a pendulum)
So, my question is, if I go for a wheel that is 18lbs vs. 25lbs, am I really going to see any savings in MPG?
One wheel I am looking at, for several reasons is the stock Wilderness wheel. I like the look, I can get them for the same price as the mid range of the wheels I have been looking at($218 each), and I know they fit correctly and will not cause Subaru to point to my wheels as a warranty issue. I like the stock offset, stock lugs and no hub ring required. Only down side is they are 25lbs, so on the heavy end.
Am I getting wrapped up over nothing? Is the wheel going to really effect it, or is the MPG hit going to be all from the tires?

You are correct that the weight of the tire has a more negative effect than the weight of the wheel. Another member posted a very detailed thread on getting lighter wheels to offset the heavier tires, yet he still noticed a decrease in mpg and performance.

I don't know of any all terrain that weighs less than 30#. I also know that on a recent off-road trip with what is basically the same car as yours, I was pleasantly surprised at how well our Outback did with Continental Control Contact Tour A/S Plus tires. We did a lot of rock crawling, some small boulder crawling, and a lot of deep sand and the Outback did great. There were a few sections where I had to keep slow momentum and use X-mode, but it made it through. I finally had to turn around on a section with boulders big enough they probably would have stopped my lifted 4x4 truck. Bottom line is the Outback does amazingly good if you recognize its limits and have enough off-roading experience to make smart choices. The biggest limit is the approach and departure angle, and tires and even a lift aren't going to hep much there. I picked up a couple small scratches in one wheel where it was spinning in deep dirt and rocks, but otherwise made it through unscathed. It has helped steer me towards focusing more on better tires for winter than for off-roading for my next set of tires, because realistically I can't see the Outback doing much more than I have already put it through, and it exceeded my expectations.

If I were you I'd leave the vehicle stock and try it. If you feel the stock Yokos aren't good enough, try adding your all terrains and judge for yourself if the performance and mileage penalty justify swapping for lighter wheels. Keep in mind you'll only gain back some of that performance hit, because you already recognized the heavier tires have more impact than the lighter wheels. The stock Yokos are a decent tire, certainly better than the Duelers our 19 Outback came with. Give them a try, you might be pleasantly surprised. Good luck with your decision.

 

So called "academic" discussion....in the real life no difference....maybe just a difference of one Starbucks Latte a month. Do not sweat over it. Do what you wanted to do from the start... a compromise in the name of fuel savings will not compensate your lost "feel good" factor. (I went through the same agony before and it was not worth it)

PS Just noticed that this is my #100 post... and the best content ever... Can I get a cookie for that?

 

PS Just noticed that this is my #100 post... and the best content ever... Can I get a cookie for that?

🍪

 

Thanks, but what took you so long? (102 now) hehehe

 

Different time zones

 

While you mention MPG, another factor is the tires and wheels contribute to the unsprung weight. The ride is impacted by how much unsprung weight there is in comparison to the sprung. A pound or two (x4) is probably not an issue but bump that up to 5-10 pounds per wheel and you might notice the ride.

 

Good series of articles on unsprung and rotational weight, why it matters.
Wheel Tech, Part I: Wheel Weight Slows You Down | Tuner University

 

So, I guess a little understanding of my reasoning may be helpful. I do know that this is all going to be compromises and I am going to just have to life with what I decide.
My "Other" car is a 2008 Chevrolet Suburban. I love it, but 11.5 MPG on a good day is had to live with. Most weeks I drive 102 mile to the airport on Monday, and return home Friday(one stop light). My final destination is always different. Some weeks, like this week, I am driving my car about 400 miles each way to a customer. I do get paid for every mile I drive. With gas prices as they are, the reimbursement was just covering the cost of gas and maybe a very little towards wear.
I live in the middle of nowhere, so everywhere from my house is freeway/2 lane driving.
I have not had a "New" car in over 30 years. My job pays well, and I recently started getting a decent amount of money from the VA that allows me to easily afford this new 23 Onyx.
Part of my justification for the purchase was gas mileage, but also that I have always kept my wife in a new car while I drove the used junk. I can now afford for us both to have a new car. She has a 22 Outback Limited.
I also want to customize this car for light back road exploring and camping. I also want it to look good to me. So, new wheels and tires are going to be a big part of that. I do want it to look good, to not look like a soccer mom car, but more of an "Overlander" look. More "Manly" if you will.
So, in the end, I want it to perform good off road, this means more durable tires. I want it to look good, nice wheels/tires. I also want it to maintain decent gas mileage, otherwise the switch from the Suburban make no sense.

I think from the reading I have done, and the fact that most of my driving is all hwy, the weight of the wheel seems like it will have very little effect unless I go crazy heavy. Getting the look and the off road durability from the A/T tires is my main objective. The Wilderness wheel is still an option for me as I like the "Factory" fit of those wheels.

 

When it comes to city driving with a lot of stop and go, a heavier wheel and tire may affect fuel economy by requiring more horsepower and torque to accelerate,, but at steady high speed cruise aerodynamics are by far more important. Tesla has some pretty nice looking alloy wheels but they put this fan blade cover on it that's about 5 pounds each. Take off the cover and electric range decreases because of aerodynamics despite the weight decrease.

Stock alloys generally have a lot of flat surface area - they try to hide it, but a lot of open space in the front of the wheel increases drag as the wind catches the barrel of the wheel.

The extra power of the turbo motor may mask the slower acceleration of heavier wheels and tires, but it would be more noticeable on the naturally aspirated 2.5. 5 pounds per wheel may not feel different but 10 pounds per wheel is noticeable (at least to me).

On a truck or other vehicle with solid axles the unsprung weight is already high and an extra 10 pounds may not be noticeable for things like ride, but in a car with independent suspension with aluminum parts, the change is more significant in terms of letting the wheel and tire respond to the road.

So don't agonize over this - just realize that weight matters to some degree so avoid super heavy wheels especially if you're also getting significantly heavier tires. Weight is just one of many variables - a wider wheel is also less aerodynamic, and one that protrudes more from the wheel well (lower offset).

 

With all that highway driving, figure in that law of motion pertaining to momentum.
An object in motion tends to stay in motion.
You would have 4 "flywheels" keeping momentum.
I'm no engineer, but if someone did the calculations it would probably show that weight spinning at those speeds and distances would probably even itself out in energy used.
By offroading, do you mean that some of the "roads" you are driving on your trips aren't paved?

 

The heavy flywheel effect makes acceleration, stopping take more energy, but it doesn't increase fuel economy at steady state.

When I first saw the fuel economy figures for hybrid vehicles I was surprised to see that highway fuel economy was worse than city fuel economy, but now I realize that it's because regenerative braking stores up energy in braking that can be used to re-accelerate and wind resistance isn't a drag at low speeds, but on the highway drag is the main energy sink.

In a normal car all of the energy used to stop is wasted as pure friction/heat, so the flywheel effect of heavy wheels and tires means more heat on the brakes when slowing - that's where the stored energy goes. Rotational weight is said to be approximately 4x more than regular weight, so if you had 40 pounds (10 at each wheel) it would be roughly equivalent to 160 pounds in the car. Some resources suggest different ratios but it depends on where the rotating weight is in terms of being concentrated in the center (wheels) vs the perimeter (tires).

If you want more detail this post in a BMW forum is food for thought:

HP Gains -Understanding Unsprung vs. Sprung vs. Rotating...

There have been many discussions primarily focused on increasing the power and/or performance of our beloved e39s. To accomplish perceived power gains you basically have three or four options; increase engine power, modify power transfer to the wheels, decrease weight, decrease drag. There may...

www.bimmerfest.com

If you think of two identical carts, but one empty and the other with 400 pounds of weight, rolling at the same speed on a flat surface, the cart with 400 pounds will go further with its stored energy, BUT it will have taken that much more energy to get that cart with 400 pounds to be the same speed as the empty cart. If you put that same amount of energy into the light cart it would go at least as far.

 

The heavy flywheel effect makes acceleration, stopping take more energy, but it doesn't increase fuel economy at steady state.

I wasn't thinking it would increase economy at all, just maybe offset the added weight of the wheels with all that long stretch and minimal stop go.

 

As I recall from drag-racing..... 'Rule of thumb' is 1 pound of rotating mass is approximately equivalent to 7 pounds of static load within vehicle.

This is because, when traveling at a constant speed in straight line

• a static mass has ZERO effect
• a dynamically spinning mass is a CONSTANT load on the engine

 

As I recall from drag-racing..... 'Rule of thumb' is 1 pound of rotating mass is approximately equivalent to 7 pounds of static load within vehicle.

This is because, when traveling at a constant speed in straight line

• a static mass has ZERO effect
• a dynamically spinning mass is a CONSTANT load on the engine

This is true, but not the only dynamic at play. As nearly all of my on road driving is freeway with almost no stops, the load on the engine to get it rolling is only happening a couple of time in 100 miles. Once rolling the added weight will effect it, but not as dramatically.
I am not drag racing, and to be honest, I take off rather slowly.
With all the research I have done, it seems the design of the wheel can play a large part in MPG. The stock wheels with the mostly flat surface and small holes causes less aerodynamic drag then the open spoked wheels that the aftermarket is offering.
So, the question would be, in my situation would AT tires on the stock heavier wheels do better that the same AT tires on lighter less aerodynamic aftermarket wheels? Lighter vs. Aerodynamic?
Even if the Aftermarket wheels saved 2 MPG ( highly doubt it), the stock wheels save me $800-1200, that buys a lot of gas. At even 2 mpg, I don’t think the car or I will live long enough to get that $1000 back. So, aftermarket wheels would be for the looks, not savings.
Much to consider.