I have never seen something like this for sale for bikes meant for transport. And to be honest, I have very rarely seen bikes covered like this on a vehicle.

And I suspect that is because it is generally unnecessary and even risky.

Unless you are driving through salted roads, there is really nothing to worry about with the bikes. Just make sure the chain is lubed, and some people cover their saddles (I don’t).

The way I see it, covering them would just create problems.

Instead of the air flowing through the bikes, now you have this big sail you are trying to push sideways through the wind. Think about it: from the side, most bikes are mostly all open space, and don’t catch THAT much wind. Now compare that to the roughly 15 square feet of solid material you are now looking at in profile.

In addition to what I would think would be a huge hit in gas mileage, I would worry (as others have mentioned) what it might do to the bikes getting pushed around like that.

Edit: you will sometimes see bikes on roof racks with a “bra” over the bars and saddle, but those bikes are mounted in line with the wind, and the coverings don’t actually have much profile in the wind.