Undetectable. And don't forget, whtever aerodynamic benefit there is, is offset by the additional unsprung rotating weight of the disks themselves. We have them because they are cool. Asking about aerodynamics is like asking about the aerodynamic efficiency of the Playboy centerfold's bustline.
Hi Doc, Well, that depends on how many times one speeds up slows down, or hits a pot hole. If the main distance of a commute is cruise control at 62 mph, they could help. Closing up the fender gap to the tires will help even more. The covers I made out of 9 mil aluminum flashing weigh on the order of about 1/2 th trim rings themselves. BTW, they throw the road salty water off radially, which makes a nice pattern on the tires. Kinda like reentry thruster burn marks, only white.
