What kind of bike goes back wards when you pedal backwards?

im tryin to find a bike that can do that

A fixed-gear bike. These are single-speed bikes (drivetrain like a BMX bike, not like a multispeed bike). More expensive models are used in veledrome racing. Lesser expensive models are used by bike messengers (like in the movie "Quicksilver"). Many come with a "flip-flop" rear wheel, which allows you to ride in fixed gear or free wheel mode just by flipping the tire around. Check out the Schwinn Madison, the Giant Bowery, the Fuji Track, and many others.

a unicycle

yeah its a fixed gear bike, but if your trying to find one so you can ride backwards and spin around they dont usually have fixed gears.

A track bike will travel backward when you peddle backward since there are no brakes on a track bike and it is a one gear direct connection peddle sprocket to drive sprocket.

It's original name is a fixed cog. Mostly use as a track bike, but there is nothing to stop you putting brakes on it if you contemplate using it on the roads, although , not advisable.