单速车，区分为2种 Single speed, Fixed Gear，后者又称固定齿轮自行车、“死飞车”，是一种没有单向自由轮的自行车，车轮与脚踏板永远处于联动状态，链轮齿与轮毂是紧紧咬合的，只要后轮旋转，脚踏板也要旋转，因此不能保持脚踏板不动滑行。而single speed 则是在后轮齿盘上加装飞轮，让一般人更容易接受骑乘。

Fixed Gear 死飞车这种结构的优点是结构简单，不易损坏。刹车时可以通过重心前移用双脚脚踏板反向发力制动后轮，辅助制动。低速反向蹬脚踏板可以倒行。缺点是脚踏板与后轮连动，只要车子有动双脚不能保持不动，造成滑行时劳累。固定齿轮车通常是不安装后变速盘和变速器的单速自行车，透过向后开口的后叉钩爪去达到调整链条张力的功能，有些只配备前轮刹车器，有些不配备刹车器，只通过脚踏板制动。

A fixed-gear bicycle (or fixed-wheel bicycle, commonly known in some places as a fixie) is a bicycle that has a drivetrain with no freewheel mechanism. The freewheel was developed early in the history of bicycle design but the fixed-gear bicycle remained the standard track racing design. More recently the "fixie" has become a popular alternative among mainly urban cyclists, offering the advantage of simplicity compared with the standard multi-geared bicycle.