Steelies or Alloys?

[Chris D.]

Originally Posted by digitaldissent

I have confirmed the steels are 15lbs and the factory alloys are 17lbs, tirerack says my tires are 18.

2mpg that's awesome, I knew it. Thanks ChrisD for the info

who's got a couple of grand for me?

No problem, but tirerack states your tire in your size is 17lbs..

look for "tires" then cross refference the size..

http://www.tirerack.com/tires/Spec.j...%3D86TR5RE92V2

Couple of grand?!? what do you have in mind for wheels?
15lbs for the steelies is pretty dam good

moon them and call it done

Originally Posted by Xringer

I'll bet if you drove 25 mph in your Tacoma and measured the MPG and then
bolted 4'x8' sheet of plywood vertically on your tailgate, you would see a big
drop in your 25 mph FE.

I believe that cd is important at low speeds too. (Just ask anyone who races bicycles).
If the moons help the cd at 120+mph and didn't help some at 55 mph, I would be very surprised.
It's not like they are active device like a spoiler or VG, to my eye, they are pretty passive.
Kinda like rolling up your windows when you drive over 30.. It helps.

Your vertical 4x8 plywood tailgate setup is hardly compairable to hubcaps..

If the moons made any improvment, I'm sure EVERYONE on here would be running them.. I've read lots of a-b-a results and nothing showed any results...

my windows down vs up at 55mph doing a-b-a-b showed no signifigant change in FE on my truck utilizing my SGII and using the same distance stretch of highway..

I think my window visors have something to do with that, not sure..
thats another a-b-a test onto itself..

[Xringer]

"Your vertical 4x8 plywood tailgate setup is hardly compairable to hubcaps.. "

My point was, if the moon disc lessens the drag at 120+, it just seems logical that they will work at lower speeds too. The problem is, it's hard to measure the smaller effects.

If there is some positive benefit and costs aren't too high, why not?

[i_am_socket]

I would think that the difference of hub cap design would depend on the vehicle in question. Has anybody seen tuft testing done for stock vs disc on a particular vehicle? Has anybody seen windtunnel tests at highway speeds for the same?

Using bicycle wheels as an example (not quite the same since bikes have no fenders, but stick with me here)

High end Disc wheel: Zipp Sub9 @ 1000g
High end Spoked wheel: Mavic R-Sys @ 785g (rear)

The heavier Zipp is far more aero than the Mavic and can shave several minutes (~4) off a 100 mile course vs the lighter spoked wheel @ < 30 mph average speed on the same bike. More aero @ speed = < power output = energy saved

So, since the aero benfit can be had (negligible as it may be) at a seriously minimal cost, why not? Even if the gains are so tiny as to be nearly immeasurable tank to tank, over the life of the car it may pay for itself.

[Xringer]

Originally Posted by i_am_socket

I would think that the difference of hub cap design would depend on the vehicle in question. Has anybody seen tuft testing done for stock vs disc on a particular vehicle? Has anybody seen windtunnel tests at highway speeds for the same?
.

I'm not sure what the yarn would look like on a moon disc. But my guess is,
it would lay down in a spiral and maybe outwards towards the tips.
Depending on the yarn's weight or if a circular laminar air layer would exist on the surface of the disc.?.
Maybe do it small scale with a drill and sanding disk? Or glue a 14" coroplas disk on top of the sanding disk?

Somewhere, I've seen spinning disks where paint (in the center) flowed out to the edges, but I can't recall what the results looked like!

--

Would the wheels need to be spinning while the car was in a wind tunnel??

I think some wheels are designed to allow air to flow over disk brakes, for cooling. Maybe even force the air around the discs. With spokes acting like fan blades.

I wonder what mine are doing with the air?

Does centrifugal force (in the middle inside) fling air towards the outside of the rim? Where it exits out those 8 holes? Where it will have a dirtying effect on the air flow passing by the car?

I'm just trying to imagine what the turbulence and drag would be like, if I cut a round 2" hole in the vertical stabilizer on a model RC glider??
I'm almost positive it would have a very detrimental effect on airspeed, and the amount of control provided by the rudder..

----

I've seen pictures of those little Honda hub holes being taped over.. I'll bet there is some small positive affect.

Now I'm wondering if Zig-Zag tape just forward of the wheel wells would do anything for the cd.?.

Cheers,
Rich

[digitaldissent]

my bad your right Chris, I looked at the tirerack lots of times and my eyes always saw 18.

couple of grand yeah! wouldn't be worth changing out the steelies unless I got some real pricey 6lbs rims or something, but if I was spending lots of money I might just try and find an Insight or something

on a side note I heard old miata rims are 6-7lbs 14" and 4x100, so maybe for some others on here that might be nice


*as far as someone said depends on the car, so true. I mean for a car like mine its already pretty aerodynamic

***we need a group wind tunnel, who is going to build it? needs to be close to my house please

[koihoshi]

Haha, a wind tunnel would be pretty dang cool.

[trikkonceptz]

OK we seem to be the DIY kings, so what would it take to build a wind tunnel? Can a body shop spray booth be used? In which case what kind of air speeds are necessary to obtain results? I am sure we can build the contraption to blow out smoke in streams ...

[i_am_socket]

I think a body shop paint booth would work. Just need a way to move air up to ~55 MPH through there, get accurate-ish air speed readings, and be able to view inside (camera/window/gnome/etc). Anybody have an airboat they'd like to donate to the cause?

[ttoyoda]

OK we seem to be the DIY kings, so what would it take to build a wind tunnel? Can a body shop spray booth be used? In which case what kind of air speeds are necessary to obtain results? I am sure we can build the contraption to blow out smoke in streams ...

You mean for full size? Whoa.
Now if you are talking about 1/4 scale models or smaller, then ok.

Here is data on the MIT wind tunnel.

http://web.mit.edu/aeroastro/labs/wbwt/index.html

One of the links says that it uses a 2000 HP motor. The good news is that for airspeeds of 15 mph you only need 350 HP, but I suspect I am not reading that right.
If I were going to instument and test small models, I would start out and make a platform that stuck out in front of a car in the clean airstream, have the model on it, and drive the real car around and take data points.
(air temp, air pressure, velocity, drag/lift loads on model, for a start).
measure the loads using strain guages.

I suspect the biggest problem is that in real life, a car is moving on a stationary road surface thru stationary air. All the wind tunnel models I know of a car have the "road" not moving, AND the car not moving, which is different than what really goes on. So the airflow under the car is different in the wind tunnel vs on the road.
To make that less confusing: In real life, the air does not move relative to the road. In the wind tunnel, it does.

When you model aircraft, the "road not moving" problem does not exist.

[i_am_socket]

Or far more simply: just have a chase car and an empty road, its cheaper and easier

I did a few searches trying to find everything I could to get more data, but one interesting piece I found had to do with wheel skirts. From Gassavers - basically it seems the pumping of air from the wheels combined with a wheel skirt created pressure that messed up the airflow and reduced MPGs. Without the spokes pumping pressure in there the situation might have been reversed. Perhaps step 1 is disc and step 2 is skirt?