Modern road bike shifters are integrated with the brake levers. All of the three major component manufacturers (Shimano, SRAM and Campagnolo) have similar styles of shift/brake levers, although each one has a different feel and internal mechanisms.
The latest trend is toward single-lever, where the braking and shifting is accomplished with one lever. The rider pulls on the lever to brake, and clicks the lever to the side once or twice depending on whether he wants to shift up or down. With traditional brake/shift levers, the rider pulls on the larger of the two levers to brake, and pushes either the large or small lever toward the bike to shift.
Mountain bike shifters also come in several varieties:
- push-pull, and
- grip shift.
A push-push system uses two shift levers on each handlebar, one for shifting up, the other for down – they are both thumb-activated, leaving the rest of the fingers to grip the handlebar and brake lever.
A push-pull looks the same, but one of the levers can be operated as a push (thumb) or pull (forefinger). This is no more or less efficient, just personal preference.
Grip shifters (or twist shifters) use a twisting motion to shift, like motorcycle levers. Grip shifters are not very common among performance bikes because of how easy it is to inadvertently shift while gripping the handlebars hard in a technical section.
Hybrid bikes typically come with mountain bike shifters, either in the lever styles or twist-shift styles. Kids’ bikes usually have grip shifters because they require less manual dexterity to operate.
There are also tiny shifters that can be mounted on the ends of aerobars on time-trial bikes. These are shifters only; the rider must move his hands to the outer bar to reach the brake levers.