@D20foz Might be useful if we knew what model you have?

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@Kevin Ah how’d I forget ? Lol it’s a 2020 Forester sport 😄

 

The tires alone could contribute some, but there could be other reasons.
I went to WildPeaks from A/S radials and didn't see much of a mpg change.
Are the tires low in pressure?
Change in fuel?
Change in driving habits or traffic conditions?
Added a roof rack?

 

I think cold weather will have a decent impact as well.

 

I agree. I'm a gas-mileage-data zealot, and I calculate a running-time-average of all my tanks -- at each point in time, a calculation of minus 5 tanks through plus 5 tanks (11 tanks) worth of MPG. This greatly lessens the random variation effect of unequal tank filling levels. My car lives in the lowland PNW where winter temperatures are usually 40-50F over the 24 hours, and summer temperatures are usually 60-80F. We do plenty of short distance driving (< 5-10 miles between cold starts). I'm excluding long vacation trips in drawing my conclusion -- I would say that the weather variation effect is about 2mpg, up in the summer, down in the winter, after >4 years and 59,000 miles.

 

With your larger tires you are actually traveling farther with each wheel rotation so your car odometer is no longer accurate. You are traveling farther than your trip meter shows so it will automatically be lower. When you ad heavier and less efficient tires that add to it as you use more fuel to get up to speed, more to maintain your speed, and more to overcome the loss of aerodynamics due to being higher off the ground and having tires that stick out the side further.

 

When will subaru let you reconfigure that setting like other manufactures do.

 

I recently replaced the factory Yoko's on my 2018 with the Falken Wildpeak A/T Trails, same size as OEM. After driving 2,000+ miles on the new tires, I have noted just a 2 mpg loss in fuel economy.

 

Combination of change in tire size, tire material, wheels(material, weight), tread design ALL contribute to change in MPG. Given the fact that you went to wider tire, you creating more friction, combined with a more aggressive tread pattern for off-road use, likely heavier tire since you went with wider rims and tires. I am not surprised with the with MPG drop. Also stop n go driving makes your MPG even worse on top of the modification you made.

Maybe you need to do an ECU reset so the ECU relearns the fact that you have made these wheel and tire modification?

 

Yes cold weather has an impact on fuel consumption that's for sure. But OP is living in California if I'm not mistaken, surely winter in California is mild enough that the engine doesn't take too long to get to running temperature, no?

 

@D20foz you didn't specify which Falken Wildpeak model you had installed. There is the off-road Wildpeak AT3W and the light SUV/CUV-specific Wildpeak AT Trail.

The Wildpeak AT Trail version in 235/17R165 has an XL load rating, and weighs in at 35.1 lbs each. You did not mention which new wheels were installed, perhaps increasing the weight at each corner even more. This additional rotational weight will have a large impact on MPG. Plus with the +20 offset, your wheels are sticking out 25mm compared to stock (+45 offset) which affects MPG too.

You gain a little MPG back from the larger tire circumference (fewer rotations per mile) but that is only 4% gain compared to stock 225/18R55. So that 20 mpg you are seeing now, is really about 20.8 mpg.

 

Naidu has good advice- an all terrain tire by design (chunky and soft) will have much more rolling resistance and therefore worse fuel economy. I tried the pirelli scorpion verde on one of our cars and gained 4mpg (it’s a low rolling resistance tire).

Also unsprung weight has a dramatic effect- basically the worst weight to add. What’s the wheel+tire weight vs the stock setup? Try and lower the unsprung weight whenever you can- it effects braking, acceleration, fuel economy, ride and handling. In adding it you are asking the engine and brakes to deal with a larger rational mass, and the suspension has to control that weight on the end of a lever arm (your suspension).

If you must run a large off-road tire try and find a lighter wheel? I purchased a wheel on my forester from tire rack that was 18x8.5 vs stock 17x7 and weighed 7lbs less per wheel, 5lbs lighter with its tire vs stock. Saw a 5mpg increase on highway (huge on my little pzev 2.5 automatic) with a Thule snowboard box on top. Not sure of the rolling resistance of the tires but they are both all season touring so same basic type.

 

@Naidu @whobodym @P-Dawg @DragonSubie7
@Mrfox @oMc @bman400

Hi guys thanks for all the responses. The wheels are the LP7 ET20 from LP Aventure. Tires are Wildpeak AT3w.

After having the tire wheel combo installed, the car obviously felt more sluggish but more so than I thought it would. On different trips I would record an avg ~20-22mpg. On the highway I would record ~26.(Speedometer)

2 days ago I installed my ADF 1 7/8inch lift with multi link and I have gotten a return in power and mpg. Haven’t been through a whole tank just yet but have been recording
24.7mpg avg and 30.1mpg highway. Not much to show just yet but the car does drive a lot better. Any thoughts ? Maybe the centering of the multi link ?
Thanks for all the help guys

 

The wheels are the LP7 ET20 from LP Aventure. Tires are Wildpeak AT3w.

I looked those up -- the wheels weigh 27.9 lbs each, and the tires come in at 31.1 lbs, for a total of 59 lbs at each corner. The AT3w in that size is not XL rated, so it is lighter than the AT Trail of the same size. If I recall correctly, the OEM wheel+tire combo weighs 52 or 53 lbs I think. So that difference will show in your MPGs, especially in stop-n-go traffic.

Both come with excellent reputations, so they should be bullet proof in most conditions. The tire is also rated for snow duty, so it should do well in those conditions as well. I don't have any personal experience with either though.

How is the road noise with the AT3w? Are you planning to take your vehicle off-road -- the AT3w should do well there. Enjoy them, and please post reviews once in a while so we can all learn.