2018 Cruze drastic decrease in fuel efficiency

Heavier tires/wheels shouldn’t affect mpg on a long freeway trip. Try that, see if the mpg’s are still reduced. Heavier rotating components (like wheels tires) would show up more if the driving conditions included a lot of accelerating, esp accelerating from stops. Not much accelerating necessary during a long freeway trip at a fairly constant speed.

Also use that freeway trip to check the odometer is accurate. Sometimes messing with the wheels will affect that. Freeways usually have small signs posted along side the roadway exactly every mile. Partly to help the road crew find the exact location where they are supposed to go to work on something. At 60 mph you’ll pass those signs exactly every 60 seconds if the odometer/speedometer is correct. I rented a 2019 Corolla over the summer and I used that technique to notice the odometer was a little off on that rental car. Not much, but definitely not spot on.

How are you checking the fuel mileage?

MuchoMacho tires? Has marketing really sunk that low to use a name like that?

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The mind altering drug’s the marketing people use to come up with this stuff must not be as good as they used to be.

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well, I checked and sure enough weird names are the order of the day apparently. Cut and pasted.,.,…

Sexy Beast, MuchoMacho, Kitty Kat, and El Jefe H/T. Off road tires are Chubby Nubbys.


The weight of the rotating assemblies will have some affect on the fuel economy but not much. The majority of the decline in fuel economy is due to replacing low rolling resistance tires with odd ball replacements and wider tires than original equipment.

I suspect that half of the decline in fuel economy is due to the weather and change in driving conditions.

Ah …… Mmmmm …… Not exactly.

All other things being equal, the heavier the tire, the more the rolling resistance - ergo, worn tires get better fuel economy than new ones.

HOWEVER, the big differences in tire rolling resistance are tied to make and model. There can be as much as a 60% difference in RR for the same size.


The Cosmo MuchoMacho tires have a UTQG rating of 300/AA/A. The low treadwear rating and the high traction rating means the tires are designed for grip and not RR or wear.

The 225/40R18 is a Y speed rated, XL (Extra Load) tire. That means that not only is there extra material to get the Y speed rating, but there is even more because of the XL.

These tires ought to be awful for RR (Fuel economy.) They are also going to wear poorly. Whether they do what they were intended (grip) is not known.

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I think your fuel economy issue is well covered here. The vibration is another issue and it could be due to the wheels.

First, are the wheels hub centric? That means that the center hole in the wheel matches the outside diameter of the hub where they mate together.

If it is not hub centric, did the installer add hub ring adapters? If the answer is no to both the above, then the lugnuts are the only thing trying to center the wheel around the hub and that just doesn’t work very well, even with tapered lug nuts.

The wheels could also have a defect such as the hub hole not being centered exactly in the wheel or the plane of the hub mating surface on the wheel not being perfectly parallel to the the plane of the rim. That would essentially turn the wheel into a wobble wheel, but if it is only slightly off, you may not feel that until you get to a higher speed. This could also happen if there is any debris getting trapped between the wheel and the hub.

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Apparently, they’ve been around a long time.


Put the old wheels/tires back on. Mileage reverts to former glory? There ya go