Will the Atom work with fenders or a rack?

The Atom works well with fenders as it mounts inside the confines of the frame. Aaron has fenders on his bike (a Surly Cross-Check) and the Atom fits great. For racks, depending on the type of rack and the mounting point on the frame, there may be a need for a small spacer (~5mm). We’ve tested it on all the bikes we can get a hold of and the 5mm rule has been holding true.

How much resistance does the Atom add to riding?

The resistance is very small, and is proportional to how large your charging load is. At full generating capacity, it is akin to riding with your tires at 70 psi instead of 90 psi, or pedaling up a 0.3% grade. In our use around town, it is very difficult to tell that it’s on the bike.