Wheel cover options

[bitmap]

Hi
I would like to know your opinion on two different types of wheel covers.
I understand that consensus is, that completely smooth wheel cover without any holes is the best option drag-wise.

But recently I have come across an interview with Mercedes aerodynamicist who worked on CLA and he said that completely smooth wheels are good, but wheels with correctly placed holes are even better.

That got me confused and now I'm trying to figure out what he meant by that.
Do you think that it is aerodynamically beneficial to have some airflow through the rim and wheel cover or is it good only for brake cooling and actually makes drag coefficient worse?

I have these two options on my car:


This quite smooth wheel cover with blanked holes


or this Mercedes wheel cover which is basically a small radial fan and scaled down version of this:



So what do you think?
Which one should I use if lowest drag coefficient is what I'm after?

[NeilBlanchard]

It looks like a close call. The Mercedes may have a slight edge, especially if it is flatter.

[Arragonis]

What kind of car ? VAG (Skoda) maybe ?

Neither - the Mercedes one is from an early to mid 1990s Merc and has nothing to do with the CLA (my boss in 1994 had an E200 with those covers), the other is a standard Skoda one from the Octavia / Fabia. You can get the earlier one for very little money from most auto shops - I fitted them to my 1995 205 Turbo Diesel.

It really depends on your drive - if you do mostly motorway / highway then you can go extreme and fit a totally flat cover of some kind or just pump up your tyres, and use better technique for the most return. If you do mostly in town then better technique (search for videos here) will give you better MPG.

[deejaaa]

^^ what he said.
i don't see the need for brake cooling unless you're racing or city driving.
i am goint to get racing moons if i can justify the cost or build some for free.

[bitmap]

NeilBlanchard: both are slightly convex, Mercedes one just has some airflow through it and the other one has all openings blocked off.

Arragonis: yes it is Skoda Octavia combi TDI 1Z
I know that Mercedes wheel cover comes from W124/W201 models. I didn't mean to link it to the CLA, I just have them laying around in my garage and was wondering which one would be better to use.

I already adjusted the nut behind the wheel and done many other mods on my car. 70+ MPG(US) is my PB and 60MPG tank is not very hard to achieve

As a proper eco driver I try not to use brakes at all, so no cooling is needed.
Because I know there are many extremely knowledgeable people on this forum I just wanted to know if there is some merit to that statement or it would be better to stick with completely flat cover not allowing any airflow through.

deejaaa: living in a post-communist police state moon discs/pizza pans are not an option nere. I need something that looks OEM, so no wild aeromods for me

[aerohead]

If you compare the M-B covers to those of the 1991 100-mpg GM Ultralite,you get a fairly good balance of aero and brake cooling (panic stops,downhill mountain grades ).
Until the wheels are completely enclosed you're going to suffer some degradation anyway,so there's probably a bit of margin with respect to 'best' design.
AeroCivic is the way to go.

[bitmap]

So I did some testing today and there seems to be no measureable difference between the two types of wheelcovers

It was a nice windless day today so I did some level ground and downhill coastdowns and both types performed exactly the same. Both were very slightly better than plain 15" steel disc but I dodn't notice any difference the two types of covers.
I guess difference must be so small, that it is not possible to "measure" it by our crude methods

I also had an alignment done today and I must say that I'm very disappointed with the result.

I have done some research on toe and camber and their effect on rolling resistance and decided to go for 0 camber and 0 toe on the front axle and 1 degree camber with 2mm total toe at the rear.

Before alignment there was 0.5 degree camber and 2mm total toe on front axle and the rear was all over the place.
But after an alignment was done, car now coasts worse than before
How is that possible?
I thought that 0 camber and 0 toe was supposed to be the best setting but it doesn't seem to be the case on my car.

[Arragonis]

Given the only change is the one at the alignment place then their equipment might be out - not unusual. We had a Volvo which was supplied by the same dealer that did supercars so they did an alignment on it using the supercar garage equipment - "brilliant" I thought, it must be right.

Nope - worse, tyres wore more unevenly and handling was like driving on ballet shoes. Took it to a cheap tyre place and it was back to normal.

[bitmap]

Well, that s*cks. I had no idea that was even possible
Guess I will have to whip out the good old tape measure and check out how much did they mess it up.

[aerohead]

Originally Posted by bitmap

Well, that s*cks. I had no idea that was even possible
Guess I will have to whip out the good old tape measure and check out how much did they mess it up.

In the old days of the Mobil Economy Run,contestants would straighten out the wheels,but they were on a closed course with very low average velocities.
That little bit of tow in should really help tracking.Less fatigue on you.