MPG/ride quality loss with bigger rims

[chasej805]

So I have just picked up a 2014 grand touring and have been searching through all the wheel threads about rims to try and figure out if I should go with 22s or 21s or 20s, but cant seem to find all the info I am looking for. I saw someone who said they lost .5 mpg city and 4! mpg highway with 22s.

so for all you guys with 20s , 21s, or 22s. Can you post what your loss in MPG has been, as well as ride quality , if any? maybe even a picture with your rims so I can see it also

as well as list your rim size and tire specs.

Thanks everyone!

 

[shingles]

You will get worse MPG when you go larger. It's just physics. Not in this car, but when we went from 18 to 20's, we lost about 10% highway mpg.

 

[MikeM.]

You will get worse MPG when you go larger. It's just physics. Not in this car, but when we went from 18 to 20's, we lost about 10% highway mpg.

That's true, there is also a loss of acceleration because it robs a lot more power to spin the larger diameter wheels and causes more brake wear to slow down again.

I call that a downgrade.

 

[erhayes]

If you stay with the same Circumference, I don't think you should loose any mileage but, I would expect a harsher ride due to the lower Aspect ratio. Ed

 

[MikeM.]

If you stay with the same Circumference, I don't think you should loose any mileage but, I would expect a harsher ride due to the lower Aspect ratio. Ed

Not really. A larger rim has much more rotational inertia that must be accelerated every time you want to speed up. Of course the lower profile tire on the larger rim has less rotational inertia than the same diameter tire on a smaller rim would have. But since tire sidewalls are so much lighter than wheel rims, it doesn't come close to equalizing the situation.

Bottom line is bigger rims will always add significant rotational inertia.

 

[erhayes]

Does not the smaller tire compensate for the larger rim to some extent? The the Grand Touring with 19" wheels should get less fuel mileage than the Touring with 17" wheels and, that is not true according to MAZDA. ed

 

[Beefy]

Does not the smaller tire compensate for the larger rim to some extent?

No. Even if they were the 17" and 19" rim plus tire were the exact same total mass, shifting the denser mass of the rim to a larger radius increases rotational inertia. In reality, the 19" are both heavier and with more of the mass at a larger radius.

The the Grand Touring with 19" wheels should get less fuel mileage than the Touring with 17" wheels and, that is not true according to MAZDA. ed

You cannot trust those figures to be accurate to the letter. The effect will not be huge, but it is absolutely there.

 

[MikeM.]

You cannot trust those figures to be accurate to the letter. The effect will not be huge, but it is absolutely there.

I agree. I don't think the EPA even requires manufacturers to test every model variation like tire/wheel sizes, etc.

 

[tibimakai]

Most likely, they tell you the lowest numbers.

 

[flymo]

Does not the smaller tire compensate for the larger rim to some extent? The the Grand Touring with 19" wheels should get less fuel mileage than the Touring with 17" wheels and, that is not true according to MAZDA. ed

Assuming the same diameter of the tire overall (with a lower profile tire being used on the larger rim, of course) then the weight of the tread part of the tires would be the same. The tradoff is between additional weight in the sidewalls of the setup with the smaller wheels, and the additional rim weight in the larger ones. Not only is there more metal in the larger-diameter rims, but the spokes have to be proportionally stronger as well.

Does that mean we'd get better mileage if today's vehicles didn't all have the fashionable monster rims? In general, yes. Fashion comes with a cost.

Flymo

 

[bhq91]

Hi, Im a newbie here.I was wondering is it okay if i were to use 245/55/19 tyres on the cx-5. the total diameter of the wheel will be .9 of an inch bigger than the stock 225s.
Thats about 3.3% increase in diameter.

 

[MikeM.]

3.3% speedometer error is quite manageable (because you could mentally compensate) but the 3.3% taller gearing would concern me in terms of loss of performance and moving the shift points to a higher speed range.

Perhaps it wouldn't matter as much if you didn't have a roof-rack, gear case or other drag inducing additions. Pulling a trailer, no, not good. This kind of change could also reduce the performance of systems like stability control systems that take vehicle speed into account.

 

[bhq91]

Thanks for your answer Mike.

 

[Latitude Adj.]

So I have just picked up a 2014 grand touring and have been searching through all the wheel threads about rims to try and figure out if I should go with 22s or 21s or 20s, but cant seem to find all the info I am looking for. I saw someone who said they lost .5 mpg city and 4! mpg highway with 22s.

so for all you guys with 20s , 21s, or 22s. Can you post what your loss in MPG has been, as well as ride quality , if any? maybe even a picture with your rims so I can see it also

as well as list your rim size and tire specs.

Thanks everyone!

Yes the ride will get harsher with smaller sidewalls and a pothole has a better chance of pinching your tire and killing the rim.

As for those MPG claims, did they tell the computer the new tire diameter? Because the onboard computer is too dumb to fix the hyperflashing when you upgrade to LED's it sure isn't going to compare it's mileage to the Tom-Tom's.

 

[FiveCX-5]

Larger rims will always get lesser MPG.......but you can get a little simular to OEM, if you buy Rotary Forged wheels, they are much lighter then cast wheels.........(drive)

The TomTom will always give a difference in speed, even with the OEM wheels, because this is factory installed and given by law of security..........(in Europe)

 

[Surfsup]

The best way to measure MPG is over several tank fulls of gas, recording mileage and gallons (or km/liters) and doing the math...

 

[V8toilet]

Large wheels have high polar moment of inertia. Think of a merry-go-round with all the kids on the outside. If you try to get the merry-go-round with all the kids on the outside moving it will be difficult. Now think of that same merry-go-round with all the kids on the inside. With all the kids on the inside it would be easier to get the merry-go-round moving. This would be an example of lower polar moment of inertia. With larger diameter wheels the mass of the wheel moves out towards the edges just like the merry-go-round with all the kids on the outside. This in turn makes it more difficult for the engine to get the wheels moving from a stop or accelerating from a set speed. For this reason larger wheels cause the engine to consume more fuel to get up to speed.

Larger wheels also dull transient response. This means that the mass of the wheels don't want to change direction when you turn the wheel as compared to a lighter smaller wheel. Think of a heavy flywheel spinning and trying to move it around or turn it while it's spinning. If you have ever tried this you know that it resists change in direction. You can get around this effect somewhat by purchasing as light of the wheel as possible. As someone already mentioned you will also have a harsher ride typically.

Hope this makes sense.