Experiment: smooth wheel discs tested A-B-A - 4.6% mpg improvement @ 65 mph

[azraelswrd]

Time to retape my hubcaps then! Good find tas!

[tasdrouille]

Originally Posted by MetroMPG

Those aftermarket rims are "air blenders"!

It's interesting to note that the exposed 19 inch rim is the worst case, but when masked, it's the 2nd best case - better than the masked 17 inch rim.

To me that suggests the shrinking gap between tire and wheel arch (you can see the progression in the photos) may be having a beneficial effect. And it may be even more significant if they didn't control for tire width as well (they apparently didn't control for overall circumference, so I'd be surprised if they did control for width).

You are right about the gap reduction. An interesting thing to note is that if all wheels were also blocked from the inside, the 17 inches and 19 inches wheels would do better than the steel rim. The reason for larger taped wheels to perform less than the 15 inches steel wheel with cover is that the disk brake cover most of the wheel opening from inside airflow in the smaller one, wheras there is a huge gap on the larger diameter wheels which increases ventilation resistance a lot. It would have be interesting to see them test something like a 205/75R15 with a steel cover. I'm pretty sure that would have been the best.

The tires tested were 195/65R15, 235/45R17 and 235/35R19.

[bgd73]

to argue the very thing that has many dynamics- left rights ups downs and even backwards...weight changes, gforce side winds front winds and brakes doing four different things. Accelerating, decelerating fwd , four wheel drive, auto and manual tranny, hubs or discs, independent suspension, solid axle...heat and torque for given engine curves as well as transaxles or axle enclosed. Electrical dissipation needed or not needed....

alloy or steel is the only question I answer. Keep the hubcaps. Alloys seem to be the champ on anything, unless they are badly made, and that is very rare today I would hope.

It seems comical in comparison to the engines to smooth wheels over a balanced part that needs to simply move every direction...when all engines have a wobbling idiot called a counterbalanced crankshaft. Fix the aero wheels, use a balanced engine. Watch the aero pursuits fade away into ridicule.

[Xringer]

My tape is still hanging in there.. And after seeing that chart, I'm going to keep my tape!

[achang1]

hmm im curious is it possible to put on a pizza pan thats bigger than the rim? so that it covers part of the tires?
maybe that will help reduce the gap of tire and rim.

[MetroMPG]

Originally Posted by Xringer

And after seeing that chart, I'm going to keep my tape!

After seeing that chart, I'd be going for pizza pans.

[groar]

Originally Posted by tasdrouille

If anyone still had doubts on that one...

Thanks a lot for these data.

What amazes me is the Cd difference with speed. I though that for cars' speeds (30-100 mph) the Cd was constant.

Is the cover has a better result because it's convex while tape masks are flat with some concave parts ?
In first case the air is moved away from wheel arch and turbulence is limited.

Originally Posted by tasdrouille

SAE paper 2007-01-1047 The Influence of Rotating Wheels on Total Road Load

I wished these documents were free... Wait, they have DRM... argh
SVOBoy, MetroMPG, why not add DRM protection on EM.com ? ;-)

Denis.

[Xringer]

So, where can I find some 17" pizza pans with a 1/4" rim??
A perfect 17" would over-lap the gap, and a 0.20" to 0.30" would seal the gap nicely..

Since the center of my steel rims sticks out about 1/4" above the outer edges of the rim,
I'll need to over-lap a flap disc, or buy some 17" OD discs that are concave inside..


Hummm, Hard Aluminum Sloped Side 17" Pizza Pan S17 | Pans Screens Peels And Separators | Pizza items from Wasserstrom

Is ,18 GA ALUM thick enough for this app?

[modmonster]

check out my wheel covers and skirts.

so far its really hard to claim a mpg gain. i think it is working tough. im getting 14.2miles per litre. this is close to my previous best and i was going slightly faster with less drafting.

[Xringer]

Originally Posted by achang1

hmm im curious is it possible to put on a pizza pan thats bigger than the rim? so that it covers part of the tires?
maybe that will help reduce the gap of tire and rim.

That's what I might try to do (if I buy some pizza pans).
Since the center of my rim sticks out about 1/4 inch.
That center area is where I would need to drill my mounting holes
and a flat disc would be floating about 1/4" above the outside edge of the rim.
So, if I could get the rolled edge of the pan to just kiss the rubber a bit,
I think that might be the perfect solution for my wheel..



What do you guys think about leaving the tape under the pizza pan?
Would it help?
The only problem I can think of, is loose tape balling up on one side
and making the wheel off-balance..