Quote:
Originally Posted by Taylor95
Great answers thank you. I'm just thinking of ways that I can lower the CD on my Camry. Supposedly it is already 0.28, so I don't think there's much I can do other than adding a belly pan.
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I think a full undertray (belly pan) is the single best modificaion to reduce drag on most cars. But to do a good job, it is a lot of work. This may be relevant:
Quote:
Originally Posted by Taylor95
For the rear diffuser. Is there an optimal angle that it should slope to the bumper?
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No there isn't. You can look at a diversity of tech papers and get a diversity of 'optimal angles'. It also depends on the length (ie as a proportion of the car length) formed by the diffuser. For example, in the tech paper quoted above, the length of the diffuser is either 33 per cent, or 18 per cent, of the length of the car. Very hard to install a diffuser that is a third the length of the car!
In addition, the shape of the car (eg wagon or sedan) and the design of the undertray ahead of the diffuser will have influence.
All that said, too steep an angle will cause the flow to separate - and you don't want that. For downforce, something like 8-10 degrees , and for drag, something like 5-8 degrees
(and both with smooth floor ahead of the diffuser).
But it's pretty hard to get accurate angles working under the car, so spend your energy on making a good full-length undertray and just be sure to incorporate a gently sloping upwards bit at the back.
Edit addition: also keep in mind that aero lift that occurs differentially (ie more at the back than the front, or vice versa) will be yet another factor that influences the actual angle the diffuser forms on the road at speed. As with all car aero, the more you think about it, the more complex (and car-specific) it all gets.