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.
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.
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.
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.
Wow, just…wow. At least they’re “Kool Kat Approved”
If you got charged $150 per tire on these, you paid triple what you should’ve…well, actually, you paid $150 more than you should’ve, but that’s a separate conversation. What kind of shady mechanic would even install these?
The link maybe? I didn’t flag him, but maybe that’s why he was…(although given it was the website for Cosmo Tire’s “wonderful” mucho-macho brand I’m not sure I’d call that spam link)
I finally got new better tires. Michelin Primacy a/s. The car still vibrates. Its not constant and it comes and goes but I’ve noticed it intensifies when having to accelerate going up a hill at 70mph+. When coasting along a flat road at high speeds I don’t really notice any vibration. I don’t know if that helps identify the shaking issue.
Did you not say you still had the original tires and wheel ? Put them on and see if the vibration goes away . You are spending a lot of money with out seeing any progress . If the vibration is still there then maybe the vibration can be fixed under you warranty.
The absurdly named tires got a lot of the credit for the mileage loss… deservedly so! But cheap wheels are also no bargain. A few posters touched on the likely heavier weight and the lack of centering rings or piloting on the hub as possible problems. Basically, if you only paid around $125 a wheel, you bought cheap wheels that may be the source of your problems. The clue that you put GOOD tires on and still have a vibration problem, points to the wheels as the issue.
Cheap cast wheels can be out of balance from the factory, not completely round, not completely straight and a sloppy fit to the center pilot. If the tire shop just banged the wheels tight with an impact gun, that technique can cause a wheel to be mounted off-center. The lugs should be snugged and then torqued with cheap wheels. You might have to remove the wheels and rotate it a stud or 2 to allow for the sloppy tolerances. Easy to do if you do your own work. Very hard to get a wheel and tire shop to take the time.
