Kia Niro shows the importance of wheels on FE

[euromodder]

Having experimented with OEM "aerodynamic" wheels that weigh a lot, my advice is don't bother with them ...
On my Volvo, I could actually feel the extra weight in the steering, and more sluggish acceleration.

Go for smaller, lighter wheels , even with narrower tyres.
Narrowest allowed tyre size will still be OK

If you can make a light weight cover for an unaerodynamic but light wheel, fine

[Vman455]

Originally Posted by kach22i

The example shown on the first page of this thread as I read it has wider wheels, this would account for higher rolling resistance and higher drag.

I'll save CapriRacer the trouble of pointing out that, all else being equal, a narrower tire has higher rolling resistance than a wider tire. However, all else is probably not equal, but the wider tire doesn't have higher rolling resistance because it's wider. More aerodynamic drag, though.

[California98Civic]

Originally Posted by Vman455

I'll save CapriRacer the trouble of pointing out that, all else being equal, a narrower tire has higher rolling resistance than a wider tire. However, all else is probably not equal, but the wider tire doesn't have higher rolling resistance because it's wider. More aerodynamic drag, though.

Yup. I was thinking of CapriRacer, too. And I still suspect that the BMW i3's super-narrow & super-tall OEM tire/rim is a sign that some portion of the benefits of wider can be accomplished with larger diameter while avoiding the aero penalty of greater width. The i3 has what 19" wheels with like a 145 or 155 tire?

[ProDigit]

Makes no sense.
The type of tire does more than their size.
As long as the outer diameter is the same, the MPG should be the same.
Unless of course, you'd be comparing crappy tires with good ones.

In fact, larger rims should give you BETTER fuel economy, not worse.
My estimation is, this is just EPA ratings.
Nothing to do with real world fuel mileage.
My Chevrolet Cruze had a 32/34/40 MPG rating or something. Almost identical to the Honda Civic of the time.
Turns out my Cruze had nearly 40MPG AVG, and highway MPG was closer to 50MPG.
Honda on the other hand, had a lawsuit and fines to pay, to pay the difference to anyone owning a civic which's highway was rated 40MPG. Those people received cheques to pay the difference for cheating the EPA ratings.
Their next year model, Honda put 38 or 39MPG, which was the correct value.
Just to say, EPA values are to be taken with a grain of salt.

[freebeard]

Makes no sense.
The type of tire does [matter?] more than their size.
As long as the outer diameter is the same, the MPG should be the same.
Unless of course, you'd be comparing crappy tires with good ones.

In fact, larger rims should give you BETTER fuel economy, not worse.

You are, of course, conflating rolling diameter with rim size. There's an aspect ratio in between.

Tall/narrow gives an equal contact patch area with less frontal area, but also less cornering ability.

[royanddoreen]

I can confirm from install that larger o.d. As the 18” Niro option is has a big effect on mpg. Might consider trying a size smaller o.d. to check that effect.

[RedDevil]

Larger rims with the same outer diameter means shorter sidewall height.
Which means that when the sidewall flexes on contact with the road, it bends much sharper than a high sidewall would. Hence more friction.

Then, running them at higher than OEM pressure will have much more effect on FE, diminishing the difference with high sidewalled tires.

[royanddoreen]

Same circumference is not the case with the Niro as I stated earlier the circumference of the 18” option on the Niro is 1.1” larger than the 16” standard wheel which is unusual but i’m Thinking this is killing the mpg.

[RedDevil]

Originally Posted by royanddoreen

Same circumference is not the case with the Niro as I stated earlier the circumference of the 18” option on the Niro is 1.1” larger than the 16” standard wheel which is unusual but i’m Thinking this is killing the mpg.

Not to be pedantic, but:

Originally Posted by royanddoreen

The 18” tires have a 1.1% larger o.d. also.

1.1% is way less than 1.1", if your wheels are less than 8'4" tall.

In either case the sidewall on the 18" rimmed tires will be much narrower, so if it has to flex the same distance it will bend much sharper, and that's all extra friction.

[royanddoreen]

Originally Posted by RedDevil

Not to be pedantic, but:

1.1% is way less than 1.1", if your wheels are less than 8'4" tall.

In either case the sidewall on the 18" rimmed tires will be much narrower, so if it has to flex the same distance it will bend much sharper, and that's all extra friction.

Sorry for my shortness. 1.1% is correct which makes sense. The scenario I tried was 6% larger tire on 17” rim,about 11 kilos lighter total. I can see how low profile tires can work but usually the weight offsets the gain.