When I bought my bike the stock rear fender was removed and the tail lights and license plate relocated. This is known as a "tail chop". Cleans up the rear of the bike and looks better. However, with the license plate mounted under the tail light in the standard position (horizontally), there effectively was no longer any protection for the rear of the bike from debris flung up from the tire. Since I finally got my oxy-acetylene gas welding kit and I had some left over metal strapping I figured it would be a good reason to make a vertical license plate holder with the hope that the longer positioning of the license plate would act as a mini-fender and help protect my rear. Here is the end result:
The construction was easy. I cut the heads off two M6 x 1.00 bolts and gas welded them to the outside points of the metal bar. This allowed me to bolt the bar to the original license mounting points on the tail chop without having additional hardware showing. I beveled the outside edges to help the bar blend in better instead of it looking like it's just sitting on top.
In the middle of the bar I centered the license plate and drilled mounting holes. Next, I tapped the holes for a M6 x 1.00 thread pitch. This would allow me to screw the plate to the bar without the need for retaining nuts. Unfortunately, I didn't find any bolts that were short enough to be more flush with the bar which is why they are sticking down so far and I didn't feel like cutting the stainless steel bolts. All hardware is stainless steel and snugged down with blue Loc-tite, just to be on the safe side.
As can be seen in this shot, the original mounting bracket was not a uniform piece -- had it been then this would've been a much simpler modification. Anyway, my creation was cleaned, primed, and coated in black semi-gloss epoxy paint.
So the big question is, does it work? In a word, YES! I was surprised that the extra length, which is almost 2x the width of the plate, has enough distance to keep debris from smacking the tail. My commute takes me through a couple of wet spots where the hill-side runoff sometimes runs across the road, so whenever I cross that I get water spots and crap smattered on the pretty little tushy of my Italian girlfriend. Well, this short-skirt treatment does a far better job of keeping her clean than before so I consider it successful.
I originally had thought about a T-shaped bracket, where the vertical part of the "T" is where the license plate would be mounted. I nixed this when I remembered the time my bracket came loose: The license plate swung down on a bump, hit the tire, and got folded and thrown up into the seat pan. It wasn't until I parked the bike that I noticed it. So for the sake of safety, no vertical bar. After several days of riding -- and on bumpy, pot-holed roads no less! -- everything is solid and the license plate is in the same position (it's not like it's flappy like a piece of paper). In the event that the assembly does get loose and the plate flops down the only thing I'll have to worry about is a folded plate. I'd hate to think of the damage that could be caused if a solid metal bar struck the spinning tire...