I am many things, but a math whiz is not one of them. Still, even though I haven't seen the inside of a geometry textbook since the days of tight-rolled jeans, I know just enough about triangles to know that something's wrong with this picture:
Yes, it's sideways. And yes, that looks like the wheel of a kid's bike. But look again. Spot the design flaw hinted at in my alliterative title? Look at where the fender stays attach to the fender itself. Based on a (very) rough measurement, there's about 12 inches of fender and mudflap hanging out beyond the stays... which is about half of the total length of the fender. That's half a fender with no support. The result? Every little bump sets off an oscillation in that dangly end, causing the thing to rattle like a neglected Huffy.
The worst part is, the purveyors of this fender aren't dumb people. This is a Planet Bike, supposedly designed specifically for the Swift Folder (it lacks the cheesier -- ATMO -- hardware of the PB Recumbent fenders, so I don't think it's just one of those repurposed... although, dangitall, that cheesy hardware would have made it much easier to fix this problem now that I look at it). I have two other sets of Planet Bike fenders in the fleet in different diameters: 26-inchers on the tandem and 700c-ers on the tourer. Both have about 7" of unsupported length on about 28" of total fender... which is to say 25% dangle-factor rather than 50% (Yes, I fudged my measurements a little to make the math easier. I'm an English major.) And both can tackle washboard without sounding like I'm playing the washboard (danger, noisy link to a band I'm obsessed with).
When I feel motivated, I'm probably going to drill out the rivets, move the bracket down near the end where it belongs, and plug up the remaining holes. But I shouldn't have to.
(Just to soften the blow: The rear fender installed quite nicely and is rattle-free, since it has three equally-spaced support points around its diameter. And although I resisted the instructions telling me to just zip-tie the chainstay bridge mounting point, I have to admit that they were right -- my attempt at a no-zip-tie kludge was much less elegant, so I gave in to the Zen of Zip.)