[JulianEdgar]

Originally Posted by M_a_t_t

In one of your videos (Porsche on low drag wheel design) you say "Ventilation drag is...primarily through air passing through the openings in the wheels. Ventilation drag alone contributes up to 8% of total vehicle drag. Any difference in ventilation drag is going to be significant in terms of overall drag of the vehicle." (this isn't quite word for word, but very close) @~1:10

Then: ventilation drag is 50 percent tires and 50 percent wheels. This would suggest that 4% can be saved by putting full wheel covers on. This is double checked in the wheel graph you show later (@2:50) by a fully covered rim giving a -.015 Cd. On a car whose Cd is .30 this is a 5% decrease in drag.

In the qoute above you say you don't think it makes much of a difference. It sounds you are contradicting yourself. Maybe what you mean by "much of a difference" is different than my version? I know if Porsche went through the effort to find these results and I would assume that Honda did for the insight then full wheel covers would be worth their effort on our own cars (rather than buying a new set of rims).

I actually said "moving from a good standard wheel to one with a full cover I doubt does anything at all". I stand by that. Obviously, a really crappy wheel can be improved on, but here you see people putting full covers on Gen 1 Honda Insight wheels, etc.

Originally Posted by M_a_t_t

I would like to thank you for the compliment in wheels (again in the video) as I've put insight wheels on my mercury. What tires are you running on yours? Some have said some of the newer FE tires have worked better than the original spec potenza re92's.

I use Kumho Ecowing.

Originally Posted by M_a_t_t

On longitudinal drag: If you put wheel skirts (or spats) on the outside and enclosed the wheel well as best as you could while still allowing the suspension to articulate do you think this would mitigate most of the longitudinal drag and ventilation drag? Possibly worth 6 or 7% in the case you were making in the video?

I don't know - I've not seen any engineering data on the magnitude of drag reduction from skirts. I also imagine it would vary from car to car, and especially from wheel design to wheel design.

Originally Posted by M_a_t_t

Edit: I just watched your video on "deceptive rules of thumb in car aerodynamics" and could see a point to be made that not every car will see these results. None of the evidence I've seen has said you would get worse Cd by adding them though so they should always show some benefit. Correct?

No, not correct. Two such examples are covered in my book.