What type of shifters do I need?
Here at Canada Bicycle Parts, we like to classify shifters in 4 different categories:
Flat bar shifters are standalone shifters (ie. separate from the brake levers) which are designed to fit a straight handlebar. These include trigger shifters and twist shifters.
Flat bar brake/shift levers are a combo system packaging the shifters and brake levers together. These types of shifters tend to be less expensive then standalone shifters and brake levers selected separately, however, the obvious disadvantage is that you cannot select specific shifters and brake levers independently to get the exact setup you probably want.
For road bikes, drop bar brake/shift levers are the norm. These shifters are installed on a road drop handlebar, and thanks to smart engineering, they allow the rider to easily change gears and brake using the same lever.
Finally, for time trial or triathlon bikes, bar end shifters are designed to be installed inside the end of aero bars and offer crisp shifting in an aero position.
What is cassette spacing?
All modern shifters are indexed, meaning they have one trigger position for each gear. Also, the more sprockets there are on a cassette, the narrower the spacing between each sprocket is, and therefore the shorter the distance the derailleur must travel from one sprocket to the other. Selecting shifters designed for the proper cassette spacing (or number of speeds) is step number one to making sure the shifters will work optimally on your bike.
Double or triple shifters?
Well this is an easy one - if you have a double crankset, you'll want to select double shifters. If you have a triple crankset, well, you get the picture!
A note on mix and matching shifters and derailleurs.
The unwritten rule here at Canada Bicycle Parts is to not mix and match shifters and derailleurs from different brands. True, there are a handful of combinations that work, but the result is never better than using shifters and derailleurs made by the same company; so why not just use those?
Different derailleur / shifter companies use different actuation ratios. The actuation ratio is the ratio of cable pull to derailleur movement. For example, Sram's 1:1 Actuation means every unit of cable pulled by the shifter moves the derailleur that exact same amount. On the other hand, Shimano uses a 2:1 actuation ratio.
A Sram 1:1 shifter pulls the right amount of cable for a Sram 1:1 derailleur to change gears. A Shimano 2:1 shifter pulls the right amount of cable for a Shimano 2:1 derailleur to change gears.
In order to work properly, the shifter and derailleur must have been designed to work with the same actuation ratio in order to ensure the derailleur moves precisely from one sprocket to the other.