eBay has some great deals on bicycle frames, but you have to be sure you are buying one that fits you properly.  This is easier said than done.

First thing, sometimes frames are measured differently.  The most popular measurement is seat tube length; this can be either from the center of the bottom bracket to the center of the top tube or to the top of the seat tube.

Second thing, you have to think about the rest of the frame.  Different manufacturers will use different sizes and different geometries, making it that much harder to find the right frame size.

For example, I recently purchased a new Specialized mountain bike to replace my Giant.  My Giant had an 18 inch frame and it was perfect.  I was thinking of getting a 17 or 18 inch Specialized, but I ended up getting a 19 inch.  Turns out Giant uses slightly longer top tubes, which is why the Specialized 19 felt right to me.

I've also heard that a 56 cm Cannondale road bike would be like a 58 cm Trek road bike.

So what do you do?

Do your homework!  You can either talk to people at your local bike shop or talk to people online.  At the bike shop, just ask about differences in frame sizing between manufacturers and you'll learn a lot.  Online, I recommend posing a question at a message board like bikeforums.net.

With this info, you should be able to bid with confidence.

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