Basic advice (going from 0.33 to 0.28 on a hatchback car)

[damunk]

Hello guys,

Do you think with: (full bellypan)
1)Front undertray - with specially shaped (mercedes sls - Curved shape with exit deflectors behind wheel) wheel wind deflectors
2)middle tray - with rear wheel wind deflectors
3)rear diffuser
4)car lowered - sports look
5)wheel wells filled from inside to reduce further gap

Can reduce CD from 0.33 to 0.28 on a hatchback car? I know this question is difficult to be accurate but with some of you guys with years of experience I am sure you would have done calculations and more calculations to get a general idea and that is what I am asking for. Do you think 0.30 is more realistic.

I feel 0.28 would see not only FE significant gain but also small Performance gain. 0.05 reduction asking too much for a really well designed under body?

[aerohead]

Originally Posted by damunk

Hello guys,

Do you think with: (full bellypan)
1)Front undertray - with specially shaped (mercedes sls - Curved shape with exit deflectors behind wheel) wheel wind deflectors
2)middle tray - with rear wheel wind deflectors
3)rear diffuser
4)car lowered - sports look
5)wheel wells filled from inside to reduce further gap

Can reduce CD from 0.33 to 0.28 on a hatchback car? I know this question is difficult to be accurate but with some of you guys with years of experience I am sure you would have done calculations and more calculations to get a general idea and that is what I am asking for. Do you think 0.30 is more realistic.

I feel 0.28 would see not only FE significant gain but also small Performance gain. 0.05 reduction asking too much for a really well designed under body?

It's going to be an 'it depends' situation.
If the vehicle was a body-on-frame construction like a JEEP Wrangler, the underside would be sufficiently horrible enough that a belly pan alone might get you to Cd 0.29.
If it's a contemporary unitized chassis,the manufacturer may have already done quite a bit of cleanup under there.So it's 'iffy' with respect to the underside.
The lower the drag of the base vehicle,the more important the wheels,and there influence to overall drag.Ford Motor Company claimed that the inner fenders and wheel spats on their 1984 Probe-IV concept car was good for a 9% overall drag reduction.So you're barking at the right tree.
Most data published is for a specific vehicle tested however,and may not infer that like behavior can be guaranteed for any other vehicle given the same modification.
The best I can give you is a 'maybe.'
Perhaps you could do a rapid crude prototype,good for a limited lifespan of testing against a known performance baseline.If you see good results,then it's worth the time and effort to properly flesh it out.

[freebeard]

A rule of thumb is that improvements in Cd result in half that in mileage. So 0.05 would translate to 2.5% better mileage. So maybe 1mpg.

[Sven7]

What car are we talking about? I'd say for a 15% drag reduction you're going to be looking at more than just little tiny stuff. If you did a front air dam instead of belly pan as well as a grille block that could get you closer. Adding some rear wheel skirts and smooth wheel covers would probably do it.

[mcrews]

realllly helps to at least name the car.....it not post a picture.

[mcrews]

lower has been discussed at length in several threads.
imho it:
1. ruins the ride
2. difficult to align
3. wears out tires
4. destroys other parts
5. not worth the trade off
6. if you have increased the psi (which is a no-brainer) then the ride will really suck!

agian not knowing the car.......
look for a body kit. All the advantages and factory ride!