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Old 10-04-2009, 12:00 AM   #231 (permalink)
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Hi,

Quote:
Hey Neil, just wondering if you have a Flickr account where you can upload more images of your car.
I know it can be a real pain to have to link them here, but it's a breeze to just upload them to Flickr.
I'd love to see more images of your work !

Your doing a hell of a job. I love the new 'mirrors' !

What kind of change did you see when you took the old ones off ?

I noticed the 'zig-zag' tape that I have seen mentioned here before. What is that for ?

One more thing - I notice that you have gap fillers on the front wheel well. I wonder if it might be beneficial to channel some of that air out of the wheel well ?
( I butchered my wheel well inserts and channeled the air downwards. )

So when do you plan to add a Kammback extention ?
I will add some more pictures -- I had it in for service, so I have to retape the rear wheel skirts. I do need to update my avatar anyway.

I like the new aluminum video camera shrouds a lot better, too. I need to do some serious tape goop cleanup -- I'll try WD-40?

The idea behind the zigzag tape is like a linear golf ball dimple -- it helps maintain the slip layer. I cannot quanitfiy its affect, but it does seem to help a bit. Actually the bit at the top of the windshield was the most helpful, I think.

I have small Kammback panels installed already. I think my next step is to work on the underside of the car. It is pretty good right behind the front bumper, but there are lots of issues under there. And I think a gearing change (final drive) would be the best thing I could do now -- the 100K warranty is almost done (I just past 90K), and I'm waiting until that expires before I do any mechanical mods.

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Old 10-04-2009, 02:33 PM   #232 (permalink)
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How much do you think you can raise your mpg with a final drive of, let's say, 3.77?
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Old 10-04-2009, 04:44 PM   #233 (permalink)
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Quote:
Originally Posted by NeilBlanchard View Post
Hi,



I will add some more pictures -- I had it in for service, so I have to retape the rear wheel skirts. I do need to update my avatar anyway.

I like the new aluminum video camera shrouds a lot better, too. I need to do some serious tape goop cleanup -- I'll try WD-40?

The idea behind the zigzag tape is like a linear golf ball dimple -- it helps maintain the slip layer. I cannot quanitfiy its affect, but it does seem to help a bit. Actually the bit at the top of the windshield was the most helpful, I think.

I have small Kammback panels installed already. I think my next step is to work on the underside of the car. It is pretty good right behind the front bumper, but there are lots of issues under there. And I think a gearing change (final drive) would be the best thing I could do now -- the 100K warranty is almost done (I just past 90K), and I'm waiting until that expires before I do any mechanical mods.
Neil, I was wondering when that P.M. reply was going to arrive.

As far as maintaining the slip layer, You should already have attached flow all around. ( Remember those sharp corners in my much hated 'Cd and blunt front ends' thread ? )
When I tuft tested my Civic, I was shocked to find that the 'rain gutters' on the sides of the windshield did not channel the air in any way what-so-ever. The air just slipped right over them - and they stick up around 1/8 " or more !

Do golf ball dimples work on cars ? Everyone says no, but I wonder why it is that some car makers have dimples on the underside of their cars. The Lexus LS-400 / 430 is a famous example. Lexus used this 'gimmic' in their commercials to doop the public into believing that the dimples really work.
Strange thing though - a while back, I took a peek under a VW Jetta in a used car parking lot ( An excellent research method BTW )
I was surprised to see .... dimpled belly covers ( approx. 1" diameter )
Why would VW go through all of the trouble to add these ? Added rigidity ? Looking at the design, I would think that a corrugated design would have been more effective if that were the case. Perhaps it was done for kicks and giggles.

Whoa ... back on topic.
So, how much of an improvement have you seen with the paddle style mirrors off the car ?
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Old 10-04-2009, 08:28 PM   #234 (permalink)
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Hi,

My xA has a 4.31:1 final drive -- most of the Toyota models with the same engine and the same 5-speed transmission have a 3.56:1 final drive. This will lower the RPM's by ~17.5% and so I would hope to see most of that in increased FE at highway speeds.

I am using the zigzag tape at the edges of the A-pillar, and at the back edges of the C-pillar where the transitions are pretty drastic, and the velocity of the air needs to be slowed. I do not know if it is effective or not, but I don't think that it can hurt either.

Yes, the video mirrors and the partial front wheel skirts together have increased the best mileage from 47-48 up to 50-53mpg.

I have to take the xA back in for service (the passenger side rear wheel bearing is failing, and the new one is on order) -- so I am going without the rear wheel skirts until then. My mileage has dropped a lot -- I'm struggling to keep it above 46mpg right now.
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Old 10-04-2009, 10:24 PM   #235 (permalink)
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Even with the moon discs?
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Old 10-04-2009, 11:16 PM   #236 (permalink)
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Hi,

Yes, even with the smooth wheel covers -- the xA has particularly large wheel openings...
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Old 10-05-2009, 10:45 PM   #237 (permalink)
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Do you think it would be the same reduction if it was lowered? (or is the wheel opening huge in the horizontal direction as well? (ie not just really tall).

I know you dont want to lower it, but just a "what if" question
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Old 10-06-2009, 08:29 AM   #238 (permalink)
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Hi,

The optional wheels for the car are 17" (the stock ones are 15") and even with the lower profile tires, they are probably larger diameter. The wheel openings are almost perfect arcs -- they are very big all around the tire.

According to the interview with the BMW aerodynamics engineer, the wheel openings are ~30% of the drag.
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Old 10-10-2009, 12:17 AM   #239 (permalink)
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Hi basslover911,

Quote:
Do you think it would be the same reduction if it was lowered? (or is the wheel opening huge in the horizontal direction as well? (ie not just really tall).
As basjoos has mentioned earlier in this post, you definitely do NOT want to lower the car in anticipation of getting higher MPG's, because they have a strong chance of actually dropping from this mod.

Take a look at the PAC Car II pictures that are on-line. Notice how this car is actually 'raised' from the ground.

Raising the car actually improves the slipperyness of any vehicle, discounting the raised exposure of the tires to the frontal area of the vehicle.

Typically, the best Cd of a 'floating' vehicle high above the ground is about .04 and when this same vehicle is lowered within inches of the ground, it's best Cd now becomes .08 or so.

This is due to the ground effect, which changes how easy the air goes around the bottom side of our ideal shape.

So in summary, except for exposing more tire area in the frontal view, you can decrease your effective Cd by 'raising' the vehicle. Of course this always causes other side effects, such as decreasing vehicle dynamic stability in handling, due to the CG now being higher. There are always compromises to make!!

Hope this helps.

Jim.
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Old 10-10-2009, 09:38 AM   #240 (permalink)
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Quote:
Originally Posted by 3-Wheeler View Post
Hi basslover911,



As basjoos has mentioned earlier in this post, you definitely do NOT want to lower the car in anticipation of getting higher MPG's, because they have a strong chance of actually dropping from this mod.

Take a look at the PAC Car II pictures that are on-line. Notice how this car is actually 'raised' from the ground.

Raising the car actually improves the slipperyness of any vehicle, discounting the raised exposure of the tires to the frontal area of the vehicle.

Typically, the best Cd of a 'floating' vehicle high above the ground is about .04 and when this same vehicle is lowered within inches of the ground, it's best Cd now becomes .08 or so.

This is due to the ground effect, which changes how easy the air goes around the bottom side of our ideal shape.

So in summary, except for exposing more tire area in the frontal view, you can decrease your effective Cd by 'raising' the vehicle. Of course this always causes other side effects, such as decreasing vehicle dynamic stability in handling, due to the CG now being higher. There are always compromises to make!!

Hope this helps.

Jim.


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