Heresy! Smooth Wheel Covers- Myth Busted!!!

[Stubby79]

You could cut, sand and paint some pieces of foam to fill the larger gaps between the spokes. If they’re black, no one will notice without looking closely.

[COcyclist]

We are heading into winter here so I recently switched back to snow tires on steel rims from thin summer tires on alloy rims. I weighed the wheel and tire combinations on a digital bathroom scale and got a rough average weight for each set. The summer tire on the alloy rim was about 36.2 pounds each for a total of 144.8 pounds for all four. The worn winter tire and rim weighed 40.2 pounds each or 160.8 pounds for all four. That is only a difference of 16 pounds of unsprung/rotating weight. I really expected to see more of a difference. I always feel like the car rides more stiffly and seems to accelerate slower with the heavier wheels. Interesting.

I have new studded tires on steel rims that I will use during the worst of winter and brand new LRR tires in the shed waiting to be mounted. I purchased those before COVID hit the US but I am driving much less so I made it through the summer on the old Goodyears. Next spring I will get them mounted and report back on any change in mpg.

[aerohead]

Originally Posted by ACEL

Some ecomodders may inquire about the choice of the wheel cover mock-ups that were trialed. After reading a number of scientific articles, I decided to test the "open center - thick perimeter" wheel studied by Vdovin in 2013 and the "open perimeter" reported by Julian Edgar in his book and some ecomodder that fabricated some for his Tesla.

Attachment 28723

Attachment 28724

Vdovin, Alexei, in 2013 also commented on the results experienced in a wind tunnel with these types of wheels :

Attachment 28725

It is not fun to read an engineering thesis but Tesla came to the same results that were well summarized by Vdovin. He was supported in his research and working with engineers and aerodynamicists of Volvo. The people of this company sometimes come up with great ideas and innovations.

Cheers ecomodders!

The 2012, Coventry University research on annular rings with the full-scale Jaguar XJ reported that they 'can be more effective than using discs,' however the results showed the disc producing lower drag.
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Tata Motors European Technical Center's 2012 research on wheel drag for the Opel Calibra and Audi A3 indicated that 80% of wheel drag originated from the portion of the wheel extending below the belly of the vehicle.
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Goro Tamai, in his book, 'The Leading Edge,' commented that, from his experience with the MIT solar race car program, that a full wheel fairing package could ( did ) reduce wheel drag by up to 70%.
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Cranfield University, with respect to their 2012 research on faired wheel aerodynamic drag, indicated:
* uncertainty
* total drag for a rotating wheel was higher
* opposite results were obtained at a different wind tunnel
* at two wheel fairing depths, drag of the rotating wheel was virtually indistinguishable from the stationary wheel.
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with respect to the on-road wheel testing of the Tesla in Germany, 'convex' discs, similar to the MOON wheel cover were never evaluated.
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With rolling-road wind tunnels available to them, and in spite of any availability to 'superior,' aspirated wheel covers of their own design, General Motors, Ford Motor Company, Volkswagen AG, and Hyundai-Kia Motors, all chose the MOON, full, convex disc wheel cover for their Bonneville Salt Flats land speed record cars. Curious.

[Vekke]

I have studied all the free tests on this topic and one of the latests tests still say totally smooth is the best on that currenct tested body.


http://publications.lib.chalmers.se/...512/250512.pdf

- I say less you have the wheel open the better.
- Also some of those chalmers study tests use as a test wheel normal aluminum wheel, which is then covered with add on test covers. If you just put cover on top of normal wheel it will still create turbulence through the inner side of the wheel. Plus it will require force to push the air out of each pole on each revolution. --> not good.
- None of the new study test have tested to find out how the convex wheel cover effect.

- Best results is with steel wheel. Pole thickness minimal and also inner side of the wheel is almosts smooth.
- Aerodynamic convex wheelcover with minimal cooling holes on the outer edge of the cover. Like the XL1 covers.

My version looks like this:

https://www.youtube.com/watch?v=rXAVfvNYy8g

That is best in most cases. Of course the results are not some in all vehicles and thats why its better to test it yourself. I have done also lot of road testing and if its windy I would say better not test at all as you cannot estimate wind direction effect to your results.

Only reliable way to test changes is ABA testing on the same day and route with as fast changes as possible. Car can take up to 100km to fully warm up in tire testing! So when you get the car warm changes should take the exact same time to do. If you let it cool 10 minutes more to other direction the temperature of the warmed parts is not anymore same.

I have custom ecu program which limits injection to certain level and you can measure the test distance and after that measure the avg speed of the test. This makes it possible to test also on hilly roads.

[Vekke]

On this report is ID3 measurements (from VW I think) for wheel drag and the best is fully blocked wheel.
https://www.bolidenforum.de/artikel/...oautos-vw-id-3

[COcyclist]

Originally Posted by Vekke

On this report is ID3 measurements (from VW I think) for wheel drag and the best is fully blocked wheel.

I would agree, it looks like fully blocked is best in this study. What stands out to me is that even the highest drag 20" rim is only 0.008 worse than the smooth reference. That is not really "low hanging fruit".

I keep hoping others will A-B-A test and add to this post. FWIW I did get the Ecopias mounted and hope to do more testing soon.

[JulianEdgar]

Originally Posted by COcyclist

I would agree, it looks like fully blocked is best in this study. What stands out to me is that even the highest drag 20" rim is only 0.008 worse than the smooth reference. That is not really "low hanging fruit".

I keep hoping others will A-B-A test and add to this post. FWIW I did get the Ecopias mounted and hope to do more testing soon.

So, worst = about 3 per cent of total drag.

[ptjones]

Seems to me I have read .04% and I get 2 mpg better with my CMAX which also has rear wheel well partial covers.

Paul

[Vekke]

Originally Posted by JulianEdgar

So, worst = about 3 per cent of total drag.

They are showing delta cd. and the wheels shown there are as aerodynamic as oems at the moment are able to make them. If you try to put just some aftermarket 20" wheel on your car no chance to get even close to those figures.

[JulianEdgar]

Originally Posted by Vekke

They are showing delta cd. and the wheels shown there are as aerodynamic as oems at the moment are able to make them. If you try to put just some aftermarket 20" wheel on your car no chance to get even close to those figures.

You seem to be arguing a proposition that was never put.