Smooth wheel covers, measureable gains?
 

I just ordered the smooth racing wheel covers from JC Whitney for my Yaris (same ones ketelone has). The stock Yaris hubcaps look very draggy. Since the top of the hubcap is travelling at 120mph when car speed is 60 mph (approximating here), and aerodynamic drag is proportional to speed squared, it seems like it could have a significant effect. Has anyone been able to get a quantitative FE gain yet?
If not, I will report numbers when I can find a good testing area. Sounds like a good excuse to go out to the Black Rock Desert playa and do some land speed record attempts.

During this winter I might make up a set of flat wheel covers (hubcaps) and rear fender wheel arch covers to suit my Suzuki Swift (aka Geo Metro) out of fiberglass.

The winters are long dark and cold here , a good time to be in the workshop.

I've had no measureable FE gain over the last 2-3 tanks...

Hummmm I guess I could just take my spokey wheel covers off and run the steel rims with holes and no paddle wheels and see if there is any difference.

I have not seen a difference that is noticable either. I do think that at higher speeds they would be more useful. Since we attempt to keep our speeds down and deal with traffic the "benefits" are not as great. Also I have no idea at what speeds it would be noticable, just seems that if they are using a similar design at the salt flats speed must be a factor.

I saw someone mentioned doing a top speed run to quantify aerodynamic improvements. I don't remember who said it, but it sounds like a very good idea. At high speeds like 100 mph, aerodynamics are far more significant than anything else. Even a 1% change in aerodynamics could be easily measured in a A-B-A-B type test which would be easy to do since top speed can be measured in a few minutes. I live in Nevada which has some perfect highways to do testing like this, and mornings are usually wind-free. I might try it if JC Whitney ever sends me my smooth hubcaps. One problem is the car might be governed to limit speed. If that is the case, I could just set the cruise at 100 mph and average the FE over a mile distance.

Ok then .....

https://www.nationaljunkband.com/njb_hubcaps.jpg

Some rather odd people that like wheel covers

2 of those hubcaps are off of a 1974 Ford Pinto!

100mph MPG testing. I like it. Not exactly "real world" but i think you will see a difference at that speed.

I gotta believe that if we can see a difference with the rear view mirrors off then the hubcaps have to make some difference too.