Mountain biking gears are a critical part of the bike. They work the hardest of all parts and are the reason why mountain bikes can go where they do. Mountain bike gears setup and adjusting is really quite a simple bike maintenance procedure. There are a few basic rules that need to be followed to differentiate between setup and adjusting derailleurs. The difference is that the setup items are done only once and never again unless the part is removed or replaced.
All new Shimano gear parts come with setup manuals which are very clear and well laid out explaining how to setup a derailleur and shifters. Both Shimao and Sram manuals are available online, see links below.
If your gears have never worked properly from the start then they probably have not been setup properly. If you had your gears setup properly and they worked fine, but now things are not working properly anymore then something has changed. This could be due to a variety of gear shifting problems.
Mountain Bike Gears Setup
Many bikes now only have a single chainring so then you won’t even have a front derailleur. Mountain bike gears setup for Shimano and Sram are similar, we have shown Shimano here.
The front derailleur is the simplest to setup and adjust. There are two setup steps here
Setup: Once these setups have been done they should never have to adjusted again unless something breaks or is replaced. Even changing cables will not require these setups to be done again
1: Position on seat tube: The front derailleur is fixed to the seat tube and should be parallel with the chain rings. The outer bottom edge of the chain guide should be 1-3 mm above the teeth of the largest chain ring when it shifts over the chain ring.
2: Cable tension: With the derailleur all the way down above the small chain ring and the shifter all the way in i.e cable longest, connect the cable, pull tight and tighten screw.
3: Hi and low settings: The hi and low settings position the end limits of the derailleur.
With the chain on the small chain ring in the front and large ring at the back. The chain should just not touch the inside inner derailleur guide. Adjust the L setting screw to achieve this
Now shift the chain to the big ring on the front and small ring on the back. The chain should just not touch the inside outer derailleur guide. Adjust the H setting screw to achieve this.
Adjusting With the derailleur on the middle ring front and back adjust the cable tensioner at the shifter so that the chain is in the middle of the derailleur.
Setup: Once these setups have been done they should never have to adjusted again unless something breaks or is replaced. Even changing cables will not require these setups to be done again.
This setup is for a normal type rear derailleur, for a reverse type derailleur the operations will be reversed.
1: Fit to the frame: The rear derailleur is connected to the derailleur hanger (dropout) on most mountain bikes.
2: Hi Lo set screws: This is best setup with the chain removed and the cable not attached This allows proper alignment of the top and bottom settings for the derailleur. Use the L (low gear) screw to adjust the derailleur to be lined up with the biggest gear on the cassette. Use the H (high gear) screw to adjust the derailleur to be lined up with the outer edge of the smallest gear on the cassette.
3: B-tension: The B-tension screw on the back of the derailleur sets the tension of the derailleur and the resulting gap between the pulley wheel and cassette. Set this up with the chain on the small chainring (front) and large sprocket (back), and then the small sprocket (back). The guide pulley should just not touch the sprocket. This is often preset and seldom needs to be set, and almost never needs to be reset.
4: Cable tension Make sure that the shifter is in the correct position with no pull on the cable (in the high position), then tension the cable and tighten the cable bolt on the derailleur.
Mountain Bike Gears Adjusting
Adjusting: If setup properly there should be no need for this adjustment. With the chain on the middle chain ring and the second smallest gear on the cassette you can check the cable tension. The chain should shift easily up and down from this gear. If it does not shift up then tighten the cable at the barrel adjuster (turn anticlockwise), or loosen (turn clockwise)if it does not shift down. Only make small adjustments, ¼ turn at a time, then shift a few times to test.
Gear Shifting Problems
Gear and Brake Cable Fitting
Check out our Mountain Bike Maintenance and Repair Guide for the next step in maintaining your bike.