Thumb shifters (Rapidfire and Topfire from Shimano).
The RapidFire shifters from Shimano (Fig. 54) are attached on straight steers to the brake lever and operate with the thumb.
The switch has two levers. One for upshifts and one for down switching.
The adjusters are on all switching positions in the same position.
With Nexave Shimano systems, Tapfire switches are used.
With these switches are the levers replaced by buttons.
When this button is pressed, the rear derailleur switches to a larger sprocket.
If the button for the front derailleur is operated, then there will be swiched to a smaller sprocket.
Thus: a lighter gear is switched by operating the buttons.
The advantages of this type of switch is that the switching is very light, and that you can brake and switch at the same time.
The disadvantage of the thumb switch, is that it is a complicated construction.
As a result, thumb shifters are sensitive to dirt and go broke faster than the structurally simple rotary switches.
Although it is possible to seperate the mechanism from each other, this is not wise.
It takes too much time to mount up for all components (especially the assembly of the various springs is tricky.)
If the switch fails to operate the protective cover must be removed properly and the parts must be cleaned and re-lubricated with Teflon. If that is not sufficient, the switch must be replaced in its entirety.
The XTR version of the Shimano thumb switches can be equipped with controls for the cycling computer.
This may be the Flightdeck computer by Shimano.