Impact of Wheel Style on Range

[dafuzztsu]

I've seen a lot of posts on here about the range impacts of shifting to a different size wheel/tire combo, or shifting from summer to all season tires. I'm curious about the design of the wheels themselves. Does anyone have thoughts or information about the impacts of different wheel styles (ex mesh vs open wheels) on efficiency. And, would that impact be enough to even notice/measure?

For reference I've seen tests where Tesla owners tried the standard 18" wheels with and without the aero covers and saw a measurable difference. Would more spokes (mesh) improve aerodynamic efficiency? Would the higher weight introduce more loss due to increased rotational inertia? Which effect do you think would be more significant?

There might not be a clear or data-driven answer but I'm curious what the hive mind thinks.

Mesh example (more surface area, but also likely heavier):

Open Example (more open area, but likely lighter weight):

*Please note: these are just google image search results, not specific wheels I am considering. They're just for visual reference to better explain what I'm on about.

 

[android04]

Probably not easy to tell just by looking at the wheels which will be more aerodynamic and by how much, because wheel offset and wheel width matter. So does the sidewall shape of the tire.

 

[MaxS]

I picked up some TSV (Uberturbine style) 19" wheels from T-Sportline about a year ago to install on my 2018 Model 3 Performance, and made some interesting observations. Below around 45mph, the TSV wheels are significantly more efficient than the (at the time of purchase) stock V1 sport 20" wheels. However, above that, they become exponentially less efficient, culminating at 400Wh/mi at 78mph. I also purchased some TS5 (open-spoke style) 18" wheels, and noted that they were more efficient at all speeds than the original wheels.

I hope this helps answer your question!

 

[gearchruncher]

Unless you are running exactly the same tires on your 20", 19", and 18" wheels, with exactly the same section widths, you cannot be sure it's due to the wheel shape.

Even with that, you still can't be sure it's wheel shape, since you're changing wheel diameter at the same time.

 

[rayrevolver]

The generalized answer: More holes in the rim = worse aero.

I was surprised at how many buses in Europe now run aero wheel covers:

Some light reading (which I have just skimmed). Includes data on full covered wheels vs 90%, 65%, and 40% coverage. Also lots of cooling discussions. Its very technical BUT you can find some graphs which show the coefficient of drag of the above wheel cover configurations.

https://research.chalmers.se/publication/510629/file/510629_Fulltext.pdf

I believe that lighter wheels are more beneficial with stop and go driving. The aero wheels help at higher speeds. The 18" Tesla wheels kinda give you both a decently light wheel and the ability to run an aero cover.

Below are my knockoff aero covers on 18" Tesla wheels (and I will again state that everyone hates these except for a random guy at Autozone). I have no idea how much difference there is with the standard cover. I just like they way they look and assume they are at least equal to Tesla covers.

 

[gearchruncher]

I believe that lighter wheels are more beneficial with stop and go driving.

We have regen. Where does the energy go in the heavier wheels?

Includes data on full covered wheels vs 90%, 65%, and 40% coverage.

An 18" wheel inherently has more "covered" area than a 19" or 20" wheel because much more of the diameter is tire, so all of the impact you are seeing could be from that, not the wheel spoke shape.

 

[dsgerbc]

Ugly wheels are more efficient. Prove me wrong

 

[tlr1000]

Ugly wheels are more efficient. Prove me wrong

 

[rayrevolver]

We have regen. Where does the energy go in the heavier wheels?


An 18" wheel inherently has more "covered" area than a 19" or 20" wheel because much more of the diameter is tire, so all of the impact you are seeing could be from that, not the wheel spoke shape.

Heavier wheels require more energy to accelerate.

Are you arguing that with Regen the heavier wheels will return more energy? I don't understand what you are getting at.

The article I posted doesn't compare 18 vs 19 wheels. But yes, the math shows an 18" wheel face has ~11% less open area. So sure, all things equal, the 18" will be a little more aerodynamic.

A screen shot of the wheel covers they tested (not showing the full 100% cover, which looks like an old moon wheel).

From the research:
It was found that, the coverage area had the greatest effect on the
drag coefficient, where increasing the coverage area decreased the
drag coefficient. An equation was found to describe this relationship,
and it was found to be inversely proportional, regardless of the
cooling flow configuration. The flowfield, pressure measurements,
and numerical model showed some reasons for this relationship;
increasing the coverage area typically reduced the flow through the
rim that otherwise fed the jetting vortex. As a result, the drag caused
by the jetting vortex was reduced. An increasing coverage area also
increased the base pressure, thereby directly reducing the pressure
drag of the vehicle.

This other attached picture came from the Internet somewhere and I had saved on my phone. Note that it calls the base wheel 100% and the 0% free area wheel cover is a solid disk.

 

[gearchruncher]

Heavier wheels require more energy to accelerate.

Are you arguing that with Regen the heavier wheels will return more energy? I don't understand what you are getting at.

Yes, heavier wheels return more energy as you decelerate as well. That's the point of regen- that you get back the kinetic energy used to accelerate.

Now, regen is not 100% efficient, so I will give you that *technically* heavier wheels do take some more energy. But let's look at the scale:

4,400 lbs at 60MPH is 718kJ joules of energy. 50 lb tire+wheels have about 11kJ each at 60 MPH. 40 lb wheels+tires have about 9kJ (because the wheel weight change is not at the max radius).

Assume a 90% regen efficiency. With heavy wheels, when we stop we recover 686kJ. With light wheels we recover 677kJ.
So if we accelerate to 60 MPH then stop with heavy wheels, we lose 75kJ. If we do it with light wheels, we lose 74kJ.

That's really not much in the scheme of things. To put it in perspective, 1kJ is 0.3 watt hours. This is the same as driving an extra 6 feet at 55 MPH from aero drag.

Also, to put into perspective just how much aero dominates acceleration/deceleration losses. If you floor it to 75 MPH, then let regen recover all that energy, and we assume it's only at an awful 75% efficiency: That's a loss of 225kJ. That's 62 watt hours. That's the same as driving a quarter mile at 55MPH. Regen really is a huge game changer in efficiency, which is the whole reason hybrid cars work.

A screen shot of the wheel covers they tested (not showing the full 100% cover, which looks like an old moon wheel).

They always took a 5 spoke wheel and widened the spoke. The OP claiming that they moved from a 12 wide curved spoke wheel to a 10 spoke open and that they can tell it changed aero efficiency. Despite also changing diameter, tires, and observing massive changes below 45 MPH where aero is irrelevant.

I'm not saying wheel aero doesn't matter. I'm saying that specific experience has way too may variables to give us any information about what wheel shape is most efficient.

 

[afadeev]

The generalized answer: More holes in the rim = worse aero.

True, but more holes in the rim == lighter wheel, thus marginally more efficient.

Yes, heavier wheels return more energy as you decelerate as well. That's the point of regen- that you get back the kinetic energy used to accelerate.
[...]Assume a 90% regen efficiency.

You get back SOME of the kinetic energy with regen. There are significant losses.
The actual regen efficiency is reported be in 60-70% range.
So heavier wheel is always less efficient.

The other, larger, problem with heavier wheels is that weight is side effect of cheaper construction with cheaper (cast) metal.
Cast wheels, in addition to being heavier, are also much more prone to bending and cracking. But they are cheaper, so Tesla is using them. Thus the 20" wheel fragility problems.

The LARGEST impact on efficiency and range comes from the tires, not the wheel.
18" and 19" wheels Tesla wheels come with cheaper all-season tires. 20" come with sticky performance summer rubber, that significantly improves traction at the cost of efficiency.
If you put Michelin PS4S tires on 18" or 19" Tesla wheels, their efficiency will go down, but performance and safety will go up. That trade-off and causal dependency are obscured in tire size vs. efficiency discussions (and by Tesla in its range disclosures).

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[gearchruncher]

So heavier wheel is always less efficient.

Yep, I said exactly that:

Now, regen is not 100% efficient, so I will give you that *technically* heavier wheels do take some more energy. But let's look at the scale:

Also, to put into perspective just how much aero dominates acceleration/deceleration losses. If you floor it to 75 MPH, then let regen recover all that energy, and we assume it's only at an awful 75% efficiency: That's a loss of 225kJ. That's 62 watt hours. That's the same as driving a quarter mile at 55MPH. Regen really is a huge game changer in efficiency, which is the whole reason hybrid cars work.

Ok, so let's re-run the wheel numbers with 65% instead of 90%:

4,400 lbs at 60MPH is 718kJ joules of energy. 50 lb tire+wheels have about 11kJ each at 60 MPH. 40 lb wheels+tires have about 9kJ (because the wheel weight change is not at the max radius).

Assume a 65% regen efficiency. With heavy wheels, when we stop we recover 495kJ. With light wheels we recover 490kJ.
So if we accelerate to 60 MPH then stop with heavy wheels, we lose 267kJ. If we do it with light wheels, we lose 264kJ.

That's really not much in the scheme of things. To put it in perspective, 3kJ is 1 watt hours. This is the same as driving an extra 18 feet at 55 MPH from aero drag.

18 feet at 55 MPH takes 0.2 seconds. And if you drive 5 miles between accelerations from 0-55 MPH, you added 0.07% efficiency. Which is the same efficiency gain as driving 0.02 MPH slower over those 5 miles. Which itself would only add 0.2 seconds to a 5 mile trip. And the longer you drive, the less the wheels matter.

Wheel weight just flat out doesn't make a difference in the car's efficiency, which is totally dominated by drag that occurs while you're moving, not just while accelerating. This is aero drag, and as you say, tire drag.

I know tire drag matters. I run 265 PS4S's on 19" wheels, and this is my efficiency: