I recently upgraded my fixed gear bike to an odd gear ratio and now the chain

[JonathanSabutis]

doesn't fit? Help!? If I remove a link it is two small. If I add a link it is too big.. am I missing something? Do I need a chain tensioner? Or perhaps a new chain?

The new cog size is 17. The new chainring is 48. The bike is a cayne uno with horizontal dropouts and a flipflop hub.

[bikeworks]

If you have horizontal dropouts there should be plenty of room- at least 1" (25mm) of adjustment which would easily allow for proper chain length, so I am assuming that you are a little confused between horizontal (sliding) dropoutsd and vertical ones. This is pretty common, actually.

Anyway, if you do indeed have vertical dropouts that don't allow you to slide the wheel back then yes, you need a chain tensioner.