The gear levers, front derailleur and rear derailleur together form the main elements of the gear system on mountain bikes, road bikes and city bikes. Whilst most systems are very similar, gear levers tend to differ. Modern shift components offer
smooth gear changes with up to 12 gears on the rear wheel and three chainrings on the crank. Road e-bikes usually posses ergonomic gear levers which also act as grips on the handlebars. Several high-end manufacturers of bikes offer electronic gear shifting. It is possible to combine assemblies from different manufacturers.