Larger lighter tire vs smaller heavier tire
 

Looking to get some new tires this summer and I’m contemplating size vs weight. I currently have heavy mt tires and wish to gain some mileage back. What I’m proposing is a change from:

285/70/17 Falken wildpeak mt load C 32.8” 62 lbs

To:

285/75/17 Firestone destination xt load D 33.9” 53.7 lbs

So gaining about an inch in height but losing about 8 lbs per tire.

Any speculation as to what effect this new taller but lighter tire would have on MPGs? Stock gears.


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A milder tread and lighter weight, but larger diameter. From having lots of different tires on 4wd trucks and SUV's, I'm going to guess there won't be much difference in MPG between the two.

Maybe a slight improvement.

no measurable improvement. any improvement from the weight savings will be so tiny that the multitude of other variables and their impact on fuel economy will come into play (what else you're carrying, what direction the wind is blowing, what you ate for breakfast, etc.)

if we just look at weight, thats 8 x 4 = 32lbs total weight savings. really not very much, less than 1% MPG improvement at the very very best and less than a penny on cost per gallon

From everything I've read on forums, it seems that deviations from stock always result in MPG reductions. I don't think I can recall anyone ever saying their mileage stayed the same or improved with an increase in tire size.

That said, since you already have tires that are larger than stock, I would speculate that the larger diameter would result in an MPG reduction. I agree that the effect of the actual tire weight would be almost meaningless.

I put BFG KO2 in load range E in stock size on my 4Runner. Heavy tires. I did not notice any significant degradation of MPG.

What is more important, IMO, is what you intend to do. I got the load range E because I do off road in western Colorado where the rocks are sharp granite, rather than the softer sandstone around Moab.

Interesting, I've never heard western Colorado offroaders talk about how sharp their rocks are, that's usually what I hear from the Arizona people. I took my '23 on P-metric Wildpeaks on the Alpine Loop near Ouray without result.

Don't expect a change in your MPG from that weight difference alone, if anything you'll maybe notice a slight difference in acceleration and braking feel. Expect changing to a different tread pattern and size will affect it more.

I'm currently running BFG KO2 285/70/17 in load range C. Before that I was running KO2 load range E in the same size, about 7 lbs or so difference per tire. So same tread design, same size, no noticable change in MPG.

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For your size change you may be saving weight but you are relocating the weight at a farther radius. IE less weight but increased inertia which counteract each other in terms of mpg changes. More inertia means more resistance to rotational acceleration.

It will probably feel a little less slugish during acceleration and breaking with slightly lower rpm ranges once you are up to speed. This is un-sprung weight savings which most people agree has a significantly larger impact on mpg than sprung weight reduction. I agree with most others here that think you will see no overall mpg change.

For reference those C load wildpeaks are pretty heavy because Falken developed them as one of the stock sizes for the Jeep Galdiator Rubicons when they first came out. I ran a set of their ATs in the same size and took a hit to mpg after that.

I switched to 255/80/17 wildpeaks after that set which is around 8 lb savings per tire. Almost no difference in mpgs :( I do love the 255s on and offroad though. Just taller than the 285/70s and it feels much lighter driving around town. Much better in snow and slush, the 285s wanted to float too much. I will probably stick with this size or go to 34x10.5 next.

I run the MT Baja Boss AT standard load in 285/70-17. 48 pounds each. Smooth, fairly quiet ride. Great reviews. I have always contemplated a 285/75-17, but the additional weight, cost, modifications, possible regear, speedometer being off as compared to the 285/70-17, spare tire fitment in the well, for ~1/2” more ground clearance is not worth it for me.

Keep in mind, too, that different size tires will affect the speedometer and odometer. Larger size tires will rack up less miles on the ODO than the actual distance traveled, which would look like you are getting poorer MPG.

Toyota vehicles, for the most part, show speedometer readings 1 to 2 MPH faster than you are really going (at 60 MPH).

Complete speculation but I'd wager no change worth talking about. I am not sure what MPG you get now but take that and add 5-10% and its such a small number that it's really nothing to celebrate.

Anything , imho, in the 285/70-75 range is going to suck. We own 2 5th gen 4runners, my wife's bone stock 2015 TEP and we can eak out high teens on the highway and mid teens intown and my 2014 TEP running 34 KM3, 4.88 gears, roof rack , bumpers, winch, sliders, gear yada yada and I will see low teens intown and mid teens on the highway.

In summary, if the Mpg is truly important, step down to OEM tire sizes, if its not just get what you prefer the look/performance of.

*not sure of the design or true size of those 285/75 but that's generally where rubbing gets more severe so keep that In mind pending what you have done to prevent rub already,

I'd agree with the group. The only example I can give is I ran the same tire in both 285/75 and 305/70 back to back. Same diameter different widths and about a 5# per tire difference. There was only about a 1/4 gallon difference in MPG

I can tell you from my line of work, offroad, tire DIAMETER is more of a power killer and fuel mileage killer than weight ever will be.
Example:
have a vehicle with 33 pound 29" tires stock
switch vehicle to 30 pound 31" tires
Vehicle gets slower acceleration and slower top speeds and worse fuel mileage
Diameter of the tire, changes how much load the vehicle senses, and will be harder for the engine to turn it.
Normally, we see going from stock 29-30" tires up to 32-33" tires. People are so invested in weight, and will take the 32" tires and shave and buff the sidewalls, lighten and sipe the treads to save weight and cut the weight of the 32" tire to as light or lighter than the OEM tire.
STILL kills power, acceleration, and top speed. A larger roll out of a tire is more load on the engine. Even if the overall weight is lighter, you are still moving the weight of the tire, belts/tread farther away from the center of the hub. The farther out you go with the weight, the larger the radius, the more power it takes to turn it.
Its been 15+ years ago but there was a GREAT video posted on YT i watched. Professional Import car track racers trying to get the fastest lap times on road courses. They changed brakes, brake diameter, and did dyno and lap times to see what the brakes changed. Smaller diameter brake rotors didnt show up on the dyno, but were measurably faster in acceleration tests on track. They also tried a ton of tire and wheel combos. They used a 15, 16, 17, and 19" wheel. They sourced different companies who had practically the exact weight wheel so they were like within 4 pounds for each set of wheels. They also sourced tires that would remain the EXACT SAME SIZE. So for the 15" wheel they had a tire that was say 28" overall and 10" wide. The same for the 16" wheel. 28" overall and 10" wide. Ect Ect for each set of wheels. This meant the only variable was the diameter of the wheel, because they tried to keep the overall mass of the tire and wheel the same. Dyno each set of wheel and tire and noticed a pretty signifigant change in dyno readings for each set of wheels. The smaller diameter wheel was noticably and measurably higher HP to the tire. The same exact results were seen on the track in lap times. The 15" wheel was measurably faster than the 16" combo. The 16" combo was measurably faster than the 17" combo, and the 19" combo was the slowest of all.

Each set of tire and wheel combo was the same overall height, and within a minimal amount of change in overall mass. Why was the larger wheel lower power on the dyno and slower on the track?

The larger wheel, moves the overall mass of the wheel (the hoop) farther away from the center of the hub, and requires more power to turn it.

The same will happen with your larger diameter tire. Your current setup has xxx amount of weight, and the larger tire, even though the weight might be lower, you are moving the weight (tire tread and steel belts) farther away from the center of the hub which will increase the load, rolling resistance, and no doubt hurt mileage and performance even more than your current tires.

This sounds like a great question to put on a calculus test.

Rotational Inertia of a tire = m*r^2

Falken: I = (28.123kg * 0.4165m^2) = 4.88 kgm^2

Firestone : I = (24.358kg * 0.4305m^2) = 4.51 kgm^2

So, the Firestone will actually take less energy to turn. The Firestone results in ~ 7.5% inertia reduction. Due to the squared radius, often the larger tire will have a higher moment of inertia however in this case the mass is reduced enough for the taller tire to be a lower moment of inertia.

If both tires have the same rolling resistance, you may be slightly better fuel economy with the firestone. I have no idea what their rolling resistances are.

In general, I wouldn’t expect to see any notable difference.