I use these Rotor Covers over the Discs of my FTB when I carry it on a Bike Rack that fits into my Car's Trail Hitch Receptacle. The FTB is oriented cross wise to the direction of car travel, so the full surface area of the rotor is subjected to Road Spray. Since we allow salt use on our roads in the Winter in MN, this salt frequently gets on the rotors of my FTB when transporting it on the Cars Rear Bicycle Rack. This in turn, if not immediately removed before I ride the bike contaminates the Bike's Disc Brake Pads and I get the "Dreaded" Noisy (squeaky) Brake Syndrome. I have used this covers several times, to protect my FTB's Rotors from Road Spray while being transported on my Car's Bike Rack. Speeds approach 70 MPH and the Rotor's where kept clean. I bought (2) other pair for my friends.
I bought these on a whim, not sure if I'd get much use out or them but they've come in handy a ton in a short amount of time. Nice knowing my rotors will stay safe while cleaning. They install and come off with ease too!
I use these whenever doing a full cleaning. Each pliable waterproof disc separates into two sheets. The inside one has a cutout to place between spokes and disc. The outside one has connecting velcro-like matching connector to the inner. Just mold around front fork and the rear around the stays. Keeps the brake discs protected from cleaning products that will make the braking squeak. Just remove and a little cleanup under and hang the covers or dry overnight. I've probably used on 25 cleanings now and I would purchase again.