Bike knowledge: How mountain bike gears work
BIKE
· 28.12.2022
This is how a mountain bike gear system works:
The rear derailleur and shift lever are the key components of a derailleur system. A shift cable made of steel mesh (for mechanical derailleurs, e.g. from Shimano) or a radio signal (as with the Sram AXS electric derailleurs) transmits the shifting impulses from the thumb to the drivetrain. Anyone who has internalised the way mountain bike gears work will find it easier to shift gears. optimal setting. We explain the most important components of an MTB drivetrain and explain the individual adjustment screws and components of the rear derailleur and gear lever.
The rear derailleur of a mountain bike gear system
1 fixing screw
The rear derailleur is attached to the rear triangle of the bike frame via the derailleur hanger using the large Allen screw at the top. The appropriate torque for tightening is 8 to 10 Newton metres.
2 Wrap-around screw
The distance between the rear derailleur and cassette can be adjusted using the wrap screw (hidden in the picture). It is located at the rear of the rear derailleur near the derailleur hanger attachment. Shimano and Sram also call this screw the B-screw. Important: The wrap must always be set in the SAG on MTB fullys!
3 Upper stop screw
On Shimano rear derailleurs, the upper stop screw is marked with an H (high gear), on Sram rear derailleurs it is the inner screw. It limits the outward swivelling range of the rear derailleur. It prevents the chain from falling onto the smallest sprocket between the frame and sprocket when shifting.
4 Lower stop screw
The lower stop screw is located under the upper one. On Shimano rear derailleurs it is marked with an L (low gear), on Sram rear derailleurs it is the outer screw. It limits the swivelling range of the rear derailleur inwards. This prevents the chain from falling onto the largest sprocket between the spokes and sprocket when shifting. The adjustment of electronic rear derailleurs works in a similar way to mechanical MTB rear derailleurs.
5 Train routing
The bushing is used to guide the shift cable with housing (Bowden cable) into the correct position on the rear derailleur.
6 Tension clamp
The combination of a screw and a small clamping plate secures the cable to the rear derailleur. The screw must be sufficiently tightened (4-7 Nm) to prevent the derailleur cable from slipping.
7 Rear derailleur springs
The arms of the rear derailleur are connected to springs, which ensure that the chain is tensioned on small sprockets in the same way as on large ones. They prevent the chain from hitting the rear triangle.
8 Switching rollers
The two derailleur pulleys are responsible for guiding the chain in the derailleur cage. Due to their exposed position, dirt often collects on them. They should therefore be cleaned regularly. They are replaceable. Coloured derailleur pulleys can be used to create visual accents.
9 Switching cage
A lateral movement of the rear derailleur is required to lift the chain onto the next sprocket. This is supported by the derailleur cage with the derailleur pulleys. The length of the derailleur cage depends on the largest sprocket of the cassette. MTB drivetrains with twelve gears at the rear therefore have a longer cage than older two-speed drivetrains with a front derailleur.
The gear lever of a mountain bike gear system
10 Upper gear lever
It is used to move the chain to the next largest sprocket. The gears are then easier to shift. Inside the gear lever is a sprocket mechanism that engages to hold the cable in the desired position after each gear change. If the lever is pulled hard, up to four gears can be shifted simultaneously. When shifting, you should take pressure off the chain, i.e. do not pedal with maximum force and shift at the same time. It should not be possible to push the upper shift lever any further after shifting to the largest sprocket.
11 Lower gear lever
Pressing the lower gear lever moves the chain to the next smaller sprocket, which means the gears become heavier. Just like when shifting up, you should not pedal at full power when shifting down.
12 Tension screw
The tension adjustment screw can be used to fine-tune the climbing behaviour of the chain on the cassette sprockets. To increase the tension, turn the adjustment wheel out (anti-clockwise or anti-clockwise). To reduce the tension, turn it in (clockwise or anti-clockwise). New shift cables usually stretch after a while. The tension must therefore be readjusted (usually increased).
With the basic knowledge, you are ideally equipped to adjust the gears on your mountain bike yourself or to troubleshoot if they are not working properly. Here you will find the right mechanic instructions for adjusting MTB gears from Sram and Shimano:
