This is going to be a short description on how to make flat aerodynamic wheel covers. I'm making these because the rounded ones from Hubcap Mike sick out too far for my rear wheel skirts. So I needed to buy or make some flat ones. Unfortunately I could not find any thing locally to buy and modify so I had to make my own. First you will need a sheet of aluminum from Lows or other hardware store. I would recommend getting the largest you can find that will fit 4 16" covers. The sheet I found was 48" long by 24" wide by .025 thick. This allows for 3 caps. They had smaller sheets but they would only fit 1 cap so you may have to buy one large sheet and one small sheet. The large sheet was $42.88 and the smaller ones were $22 something. I also had to buy some tin snips. My receipt said they were 9 3/4" 'R' Metalmaster. To make the brushed aluminum look I bought a Sand Blaster sanding sponge coarse 60. You will also need some 3M double sided adhesive tape. Some aluminum polish will also help a lot to make the caps look pretty. I also used the extra aluminum rivets I had from my other wheel cover installation. I'll try my best to describe the process because I did not take very many pictures. First off take a trim ring and lay it on the aluminum sheet. If you use the larger sheet to get three caps on it you will need to position the the trim rings with one at the top corner, then draw a circle around it with a magic marker. Then position the trim ring next to the first one you traced out near the bottom, then the next trace will be at the top. I had to cut on the inside of the marker trace then cut an additional 1/16" all around to get it to fit the trim ring. I then filed everything down smooth so I would not cut myself. Once you get the caps cut out you need to find a way to brush them to make them pretty. Since I don't have the right tools for the job I decided to use my prius as a lathe to turn the discs to get that pretty brushed aluminum look. To do that I had to mount the discs temporarily to the trim rings using the 3M sticky tape. Then I attached the the whole thing to the front wheel of the prius. Now in order to get the front wheel to spin you must disable traction control. To find out how to do that just do some searching on "disable prius traction control" and you will find it. After the little dance is done I jacked up the side of the car until the wheel came off the ground. I then put the car in drive and the wheel started to spin at the normal 7mph. (NOTE: During this process the odometer will continue to advance just like the car was moving down the road. I was able to get one cap done in about .5 miles. So expect your odometer to read about 2 miles greater after your done brushing the aluminum.) I first brushed the aluminum with the sanding pad, then used polish, then wipe the polish off, then another final brush with the sanding pad. This gave a nice clean look almost matching the caps from Hubcap Mike. Here is the before. Here is the after. Here is a side by side. My flat cap on the left and Hubcap Mike's round cap on the right. I used a putty knife to remove the discs from the trim rings. Here is the video showing how I brushed the discs. Video is 2x speed. [ame=http://video.google.com/videoplay?docid=428497399714999524]How to make a brushed aluminum aerodynamic flat wheel cover for a Prius[/ame] Now I just need to align the cover onto the ring and start drilling holes. I used masking tape to keep the disc in place while drilling. I drilled and riveted at the center of the flat spots in the location you see below. Next I drilled a small hole where the valve stem would be. Then drilled a bigger hole, then and even bigger hole. Then I used a dremel to sand out an even bigger hole and smoothed out the edges. The result is what you see here. This is the finished product. And here is what it looks like mounted on the car with the wheel skirts. I think I will have to buy some valve stem extensions to make it easier to fill the tires up with air. The holes are just big enough to fit my air compressor end into. Of course if you dont have wheel skirts you may not want to drill a hole to check the air pressure as the cover/trim rings are easy to pop off with a screw driver or plastic panel removal tool.