buying a bike in Amsterdam to tavel in Europe for 6 weeks

Obviously you would need to go to a bike store. It also depends on the type of bike. Assume you are looking for touring bikes. As avid touring cyclists we take our bikes in our suitcase but I have spent lots of time in many bike stores. This is my observation. Bikes, especially better ones, are expensive. There is a huge used bike market with most of the stores we have been in having 30,40,50 bikes for sale. But most of those bikes, both new and used, are more functional as a daily or commuting bike - heavier frames, heavier tires, more up right riding position, flat bars, etc. There are better suited for the typical road conditions in European cities. However, they may not be the typical bike that you are used to riding. If you have a good eye and are a decent bike wrench you could find something used. Don't know how easy it would be to resell at the end. Do you have a plan for carrying your luggage? Are you bring panniers?

I would price things out from here to help you make your decision. You'd want to locate the bikes you want in any case, to make sure you can buy the kind of machine appropriate for your plans. Once you have located a dealer, you can shop for quotes from a bike store in Frankfurt. Or arrange to ship them back to Amsterdam for repurchase.

Thank you for responding to my bike question. Yes we will take our packed paniers. What kind of luggage do you pack your bike in? We were going to pack each bike in an oversize box and unpack it at the airport. I have heard there is a bike path from the Amsterdam airport into the city. Do you know if this is true?

Why buy if you can rent? But in that case you're much better off with a local and cheaper shop in the province. Max Mobiel in 'nearby' Ghent (Gent, Belgium) seems to be unbeatable with a rental price of 30 euro for one month. http://www.max-mobiel.be/default.aspx?PageId=36 (Dutch)
http://www.max-mobiel.be/fietspunt (Dutch) To be considered if the German part of your trip is not too mountainous.

Wow! That is a great price to rent a bicycle for a month.
I will definitely check out the web site. Thank you.

If you can rent bikes, that would be a good thing for you. We did a similar thing in Austria. We flew into Vienna and rented bikes from a dealer there. We brought our own panniers (even our own saddles). Had a fantastic trip along the Danube. Buying bikes in Europe you need to consider the VAT tax that they charge, which can be hefty. We found renting was a great option. Best maps are from: http://www.esterbauer.com/db_rtb_allg_int.php?land_id=XE&reihe_id=RB
I am not sure if the ones you need are in English, but their maps are the best I have used in Europe for cycling.

This link will have bike journals and links to all information you may need biking in Europe...or around the world for that matter. There are forums and articles relating to all bike issues. I do not the majority of the bikers take their bikes on the planes in bike boxes. http://www.crazyguyonabike.com/?o=1 Enjoy your trip?

There is a path from the airport into town and to just about everywhere else. Paths are everywhere. Our bikes are specially designed to fit in the largest Samsonite suitcase made. Just under the limit size and weight wise for checked luggage. Have only been challenged once for having a bike and the TSA hates it. Too much steel, tubes, cables, etc. If we go somewhere to rent, we always take our own pedals and saddle. Been known to wear our bike helmets on the plane. Generally collect a few comments for wearing them.