Thoughts on wheel covers...
 

What's the consensus, is it the reduction of the volume of air that passes through them that is cut off/reduced (i.e., closing up the spokes and sealing them), or that they are flat (which does the same of course, but with the added benefit that they are flush to the tire) that is responsible for the drag the reduction?

I'm contemplating modifying my existing hubcaps by simply filling in the "spokes" and insuring no gaps between the hubcap and the tire, but this won't make them flush.

Trial it with duct tape, it will give you a ballpark of what you can expect, but minimal cost and time
invested.
Some cars have better results than others with respect to wheel covers.

Taped up the spokes, we'll see how it goes across this tank...report in a week.

Mostly closed is good, and flat and closed is better.

consensus
 

I've yet to read a complete discussion on wheel covers.
Observations have been reported and recommendations.
*An open wheel has no surface with which to 'support' airflow,so a solid surface is needed.
*A slightly convex disc won't 'tin-can',is extremely rigid for it's mass,and has a measurable drag advantage over a flat disc.
*Brake cooling should not be ignored,however solid 'MOON' style wheels have shown to be no disadvantage for many members including myself.
*The knock-on style covers are noisy and eventually come off.I've written them off.
* I was able to scrounge up a set of covers from a 1975 Buick Electra.They are absolutely 'silent,' securely hold to the wheel,and have modest ventilation for brake cooling.
*Many members have found covers which stay firmly attached which can be modified aerodynamically.

Flat coroplast circles zip tied around the spokes work well.

MetroMPG probably has an ABA test on wheel covers somewhere. I'm not sure of the % improvement but wouldn't expect more than 1mpg.

wiki link to wheel covers and data:
Smooth wheel covers - EcoModder

5 users did aba testing and got 1-1.5 gain or 2.4%-4.6% gain. not to shabby for an easy cheep mod

Well first tank down...big gain. Saw highest MPG yet, 35.88.

I simply taped over the spokes as the test. I'm working on a permanent solution:

http://www.mulsannescorner.com/pictu...2018.06.06.jpg

looks like a good start, what were you running before this tank?

The 16 week average prior was 33.59.