The Shimano 105 9-speed group set, which includes gear shifters, brakes and levers, is no longer being made by the global bicycle component manufacturer. The Shimano 105 series is now designed as a 10-speed transmission, but the operation of either group set is primarily the same. On both group sets, you shift the front ring with your left hand to make larger changes in gear and you shift the back ring with your right hand to make smaller changes. Shimano developed the 105 series for beginner road cyclist who wanted a quality group set that is comparable to high-end group sets without the high cost.
Pedal before engaging the transmission to shift gears. Maintain an even pedaling cadence to ensure a smooth chain transition. Shift gears by engaging the gear shifter and brake combination lever mounted on the handlebars. To engage this lever, push it in toward the frame.
Engage the right inner lever to the left to transition into a harder gear on the rear wheel. The chain will be fed onto the next smallest cog on the cassette.
Engage the right outer lever to the left to transition into a faster gear on the rear wheel. The chain will be fed onto the next largest cog on the cassette.
Engage the left inner lever to transition to a smaller cog wheel on the front chain ring. Shimano 105 chain rings feature two or three cog wheels on the front chain ring. A gear change on the front wheel is equivalent to several lower gear changes on the rear wheel.
Engage the left outer lever to transition to a larger cog wheel on the front chain ring. Transitioning to a larger cog wheel on the front wheel is the equivalent of several higher gear changes on the rear wheel.
Activate the brakes by squeezing the outer levers on the handlebar. Typically, the right lever engages the rear wheel brake, while the left lever engages the front wheel brake. Some bicycle models reverse this set up. Always check the set up of the brakes before riding a new bike.