I ordered some Planet Bike fenders and just installed them. They didn't come with the mud flaps (they were the cheap ones) and now am concerned they wont work 100%. Should I spend the extra $10 for them from the PlanetBike site? Thanx
No. Instead, go to your local hardware store (or Home Depot if you don't have one handy) and get a foot or so of stair-tread rubber (bathtub liner will also work, though stair-tread rubber stays more pliable in cold weather) and a roll of 3M double-sided outdoor-rated sticky tape. Make a paper template of whatever mudflap shape you'd like (or eyeball it if you're good at that) and cut it out of the material you just bought. Make sure everything is nice and clean, then affix it to the inside of the rear edge of each fender. You can attach it to the outside if clearance is tight - it really doesn't matter, though it will look a bit cleaner on the inside. You can drill a couple of holes and attach the mud flap with a zip tie or two, but I've found sticky tape to work very well - they've stayed on my bikes for multiple winters. For less than $10 in materials you can make several bikes' worth of mud flaps, and they will be a lot more effective than the ones you get from PB. Make them at least 4" wide at the bottom, and plenty long - there's nothing wrong with a front flap that is only an inch or two off the ground. It will make a big diffy in keeping your bottom bracket and feet clean.
David took the words right out of my mouth. Here's a mudflap "how-to" complete with template.
The PB Cascadia mudflaps are very nice though. It'd be worth it for the $5 for the front fender. (free shipping)
I'm sporting the stair tread flap on my townie bike. It's an easy project if you want to do DIY.