I've traveled from Austria to the US with a US bike (returning from a bike trip) and have (on another occasion) shipped three German velomobiles to Minneapolis, but there wasn't much overlap with your situation. You'll need some sort of statement of where you got the bike and what it is worth. I wonder if having evidence that you have used it for a long time would entitle you to an exemption from the presumption that you have to pay duty at a new-bike rate. You can find out about US Customs fees in the Harmonized Tariff Schedule of the United States (http://www.usitc.gov/taffairs.htm). The specific relevant section is: SECTION XVII: VEHICLES, AIRCRAFT, VESSELS AND ASSOCIATED TRANSPORT EQUIPMENT Clicking on Chapter 87, for vehicles, you come to the bicycles section, on page 15 of this chapter, headed 8712.00, "bicycles and other cycles (including delivery tricycles) not motorized"). There are a whole lot of rates quoted for various kinds of bicycles with different diameters and widths of wheels. The basic idea is that skinny-tire bikes go for 5.5% and recreational wide-tire bikes go for 11%.

Presumably, you will have to provide some evidence that the bike is yours and where you got it. Did you ever license it in the US? Do you have old photos?

If you added stuff to it in Germany, do you have receipts for the parts?

I would fill out the customs declaration with a statement that the bike was bought in the US and is being returned, would declare the value of any significant parts that added value to the bike and that aren't fully depreciated (i.e. worn out), and just send it. Plan to pick it up in person somewhere (post office, UPS or FedEx office) and to have no chance to appeal whatever amount of duty was charged.

Good luck,

Mary