Moon Caps - Any Value on 1st gen. Honda Insight? (A-B-A coastdown test)

[MetroMPG]

Ron the hybrid-battery-repair guy had used velcro to attach moon discs to his Insight, and reported no problems over long distances. I don't know how he stuck the velcro to the wheel or disc though. (Useful, aren't I!)

I'd be more comfortable with something more secure. To avoid drilling the wheel, you could fashion a sort of plug that fits through from the back of the wheel and slots into one of the openings. Then drill/screw into the plug.

You will have to time the runs, not measure their distance. Using a video recorder on the speedometer would be more accurate than eyeball/brain/stopwatch. Changing your speedometer units to km/h should be slightly more accurate still (higher speed resolution).

I still don't think you'll be able to detect any difference, above the normal variability you'll get from multiple runs. Don't let me discourage you though!

[aerohead]

Originally Posted by jime57

Well somewhere between your opinion and mine, there is a real answer

I just don't know how to get at the answer, since the difference is probably very small and nearly impossible to separate from the noise, given the difficulty of testing on an Insight.

What would you suggest? I suppose that one could do some high speed coast down test from say 70MPH to 50MPH. That would eliminate many of the Insight specific variables that confuse Insight testing. What you think of that approach?

BTW, the Moons protrude more into the airstream than the rather flat stock wheels, so there is that arguement against them. If this protrusion were productive, then Honda could easily have done the same thing with an alloy wheel. I'm just kinda suspicious that flat is better with the other work that Honda did around the fender well.

Your thought welcome

In the mod-data sticky there is some data from GM's wind tunnel development work for their Pontiac Trans Am Firebird at the Lockheed Marietta,Georgia facility.
They did comprehensive evaluations of wheel covers and their 'MOONesque' cover delivered the lowest drag.
Boeing uses them on everything they build for Southwest Airlines,and all the fastest LSR streamliners typically use them at Bonneville,as does Danika Patrick on her Indycars (both in and outside application).
The subtle convexity lowers drag (as with GOODYEAR's streamline tires for aircraft) compared to a flat disc and they are very strong for their thickness and are not subject to flutter.

[COcyclist]

Originally Posted by aerohead

The subtle convexity lowers drag (as with GOODYEAR's streamline tires for aircraft) compared to a flat disc.

When I picture this from above I see the back half of a truncated Kamm tail. Perhaps the slight frontal area penalty is more than offset by the air coming together more smoothly behind the tire phantom boattail.

[jime57]

Well, my first attempt to experimentally measure the Moon benefit, if any, failed. Tried to attach them with double sided tape. One flew off at about 60 MPH and I spent 20 minutes looking for it in the grass. Glad it didn't stay onthe road and wind up in someone's windshield

[jime57]

Originally Posted by aerohead

In the mod-data sticky there is some data from GM's wind tunnel development work for their Pontiac Trans Am Firebird at the Lockheed Marietta,Georgia facility.
They did comprehensive evaluations of wheel covers and their 'MOONesque' cover delivered the lowest drag.
Boeing uses them on everything they build for Southwest Airlines,and all the fastest LSR streamliners typically use them at Bonneville,as does Danika Patrick on her Indycars (both in and outside application).
The subtle convexity lowers drag (as with GOODYEAR's streamline tires for aircraft) compared to a flat disc and they are very strong for their thickness and are not subject to flutter.

I checked all nine pages of that thread and could not find that data.

Are you sure it isn't somewhere else?

[Sven7]

LOL, jeez. Find a way to zip tie em to the spokes

[aerohead]

Originally Posted by jime57

I checked all nine pages of that thread and could not find that data.

Are you sure it isn't somewhere else?

I found what I was thinking about at the mods-data #7 Wheels /Tires.
Larry Shinoda had a secret-weapon MOON-esque wheel cover they tested on the Trans Am 'bird.Compared to an open steel wheel they lowered the Cd by 0.027.
They were lower than the OEM wheel which ended up on the car.I thought I might have posted that comparison.I'll dig it out.

[jime57]

Originally Posted by aerohead

I found what I was thinking about at the mods-data #7 Wheels /Tires.
Larry Shinoda had a secret-weapon MOON-esque wheel cover they tested on the Trans Am 'bird.Compared to an open steel wheel they lowered the Cd by 0.027.
They were lower than the OEM wheel which ended up on the car.I thought I might have posted that comparison.I'll dig it out.

Thanks Phil. Found it.

Quote,"1982,Pontiac Trans Am Firebird wind-tunnel studies show Larry Shinoda's trick aero wheel-covers trim 0.027 off drag coefficient,compared to a open wheel."

The baseline for this test seems to be an "open wheel." I seriously doubt that the improvement would be anywhere near that great if the Insight wheel were used as a reference. It is by no means "open."

Still, I like the moons and will give them a try. Already drilled and threaded my "worst" set of Insight wheels

[jime57]

I'm having doubts about the 70-50 coastdown. The problem, as I see it, is that there are multiple forces acting on the car, other than aero drag. I've played around with the math a bit, but I don't see any way to resolve the portion attributable to aero drag. So, it is not possible to determine from the coastdown how much the aero drag is changed. It is true that the "other" factors which I can identify, primarily tire drag and drivetrain drag are constants, but there doesn't seem any way to decide on the fraction, and therefore no way to get very close to an improvement factor for aero drag.

I suppose one could resort to an approximate fraction, and that would result in a derived aero drag change.

[MetroMPG]

Why are you trying to determine Cd? Isn't your primary goal to know whether smooth wheels are better than stock wheels? You don't have to calculate Cd to answer that question.

That said, I will still be very surprised if coastdown testing shows any difference at all (too small a change to the vehicle).