For some bicycles, fenders are a large part of the bicycle’s style. For daily commuting bicycles which need to be ridden in more than just fair-weather pleasurable outings, fenders are a necessary evil. They rattle and they rub, so you adjust them, only have them impact something random, bending them so they rub again.
Last fall, after many frustrations with plastic fenders, I decided to try pressed aluminium fenders which are designed to imitate hammered metal fenders. Although I haven’t measured, the aluminium fenders feel lighter than PVC plastic fenders, but are more rigid despite it. They are also a lot more stylish.
Thin aluminium fenders do have one downside though; when sturdily installed (so as not to rattle) they amplify and project any vibration of the frame. I am a person who wants their bicycle to be silent, with only the sound of rubber on the road and the breath of the wind to be heard. Thin metal fenders disturbe this peace of the ride.
I have discovered one simple solution to this problem. Application of a suitable sound dampening agent on the inside of the fenders removes almost all of the noise! What sort of applicable material would be suitable sound dampening? So far I have tried rubber seam sealer, roofing tar and automobile asphalt undercoating spray.
When applying a coating to the inside of the fender be careful not to get any on the outside of the fender as it will ruin the finish. Note any drilled holes for mounting. It may be important not to coat these areas in case the mounting bolts are not long enough to accommodate the additional thickness of the coating, and also so the coating does not go through and again ruin the outside finish. In general, only a thin coat is needed, say never more than 1mm in thickness.
I think the rubber seam sealer is best, but also the hardest to work with. I have a pair of rubber dish gloves which are reserved only for working with the stuff as it is very hard to get off things, especially fingers.
Asphalt undercoating is a little thin, and so requires many coats. If an aerosol undercoating is used, the whole of the outside of the fender will require masking.
Roofing tar seems to be a good compromise. Its slightly easier to work with than seam sealer, both being more malleable and taking longer to set. The catch is that it can take a day to completely set, so it isn’t appropriate for a rush fender job.
So there you have it, my simple trick for quieting fenders. I would be surprised if I were the first to think of this, but I have not heard of anyone else doing this, so I thought I would document my discovery.