What is fixed gear bike?
A fixed-gear bicycle or fixed wheel bicycle, is a bicycle without the ability to coast. The sprocket is screwed directly on to the hub and there is no freewheel mechanism. A reverse-thread lockring is usually fitted to prevent the sprocket from unscrewing. Whenever the rear wheel is turning, the pedals turn in the same direction. By resisting the rotation of the pedals, a rider can slow the bike to a stop, without the aid of a brake. A fixed gear bicycle can even be ridden in reverse.
Most fixed gear bicycles only have one gear ratio. Some have a sprocket on each side of the rear hub, giving the choice of using one of two different gear ratios. Such a hub may have a fixed gear on each side (double-fixed) or a fixed gear on one side and a freewheel gear on the other (fixed-free). To change gear, it is necessary to remove, reverse and refit the rear wheel. Typically, the number of teeth on the sprockets will differ by one or two, for example 19 teeth on one side and 17 on the other, making the latter gear some 11 or 12% higher than the former (for the same chainring).
In the past Sturmey Archer made fixed multi speed hub gears allowing the rider to change gear while riding.
