> Hum. Seems to be the exact opposite of the idea of spoilers.
> And in my experience, that plastic Mazda cover is pretty tough.

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>> Hum. Seems to be the exact opposite of the idea of spoilers.
>
> I don't believe it's intended as a spoiler, simple a replacement for the
> original plastic thingy that disintegrates quickly.
It says "increasing down force by creating higher suction pressures
between the panel and road." And that is also used to support the
claim of increased cooling.
The way that people with no real knowledge of fluid mechanics selling
products often reason is that the incoming air speed in the gap between
car bottom and road is the car velocity, because it is "in front of the
car." Then they know that if you decrease the flow area, you speed up
the flow, and that Bernoulli says that lowers pressure. Unfortunately,
nonsupersonic flows are quite capable of sensing an obstruction ahead
and going around it in a more comfortable way. Having essentially
stagnation pressure below your car is not ideal. (And there are some
other problems with flow area reduction and Bernoulli, such as three-
dimensionality and viscous effects, but anyway.)
>> And in my experience, that plastic Mazda cover is pretty tough.
>
[quoted text clipped - 4 lines]
> back into shape if needed, rather than tearing as the original cover
> did. (I don't know how, it was pretty beat up when I got the car)
Driving over big stones on the million dollar highway or over exhaust
parts will do it. ;) It may well be true that the aluminum cover
might not tear and can be bend back into usable shape after an
encounter. But, IIRC, you can get about 4 plastic covers for the
price of this aluminum one. And my plastic cover was never torn so
bad that it really *had* to be replaced. And my best guess at this
time would be that there will be no measurable difference in down force
between the covers.
But I have an open mind, all of this is just guessing. I am waiting
for Bruce to tell us how right I am. (OK, wrong is also theoretically,
possible, but I consider it unlikely.)
Leon ;)

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Leon :) Bess :) Bozo .)
BRUCE HASKIN - 16 Mar 2008 00:42 GMT
I agree with Leon. The only thing I can see with this is that the sides
are open and that must do something to the air flow, into or out of the
engine area. If you put a "lip" on the rear of the plastic unit, it
would suck air "out" from around the engine, but where would the air
come from to replace it ? ALSO , under my 2003, there is a plastic 1
inch "lip" fwd of the start of the Alum. underpan, that I would guess
that Mazda uses to spoil the air flow under the car. I think I will just
need to wait a while for good weather to see what, if anything this
thing will do. :-)
I must admitttt , I bought it for show as part of my engine bay clean up
:-) If I run over someone, they can look up and say " Gee, look at thet
nice under plate ! " :-)
Bruce Bing '03 LS