Garage Files: How To Keep Your Derailleur & Cables Finely Tuned
from smaller to larger cogs, it may need a little more cable tension. If it is hesitating to shift from larger to smaller cogs, it might need slightly less cable tension. This is why at the beginning we went one full turn out on the barrel adjuster before the cable anchor bolt was tightened and had adequate tension.
Step 4: Shift the derailleur into the largest cog. If you have a bit of trouble getting into this cog, mess with the low-limit screw adjustment. The low-limit should be adjusted so the top guide pulley is aligned with the center of the largest cog. Only make small turns to the limit screw at a time to prevent the chain from falling off the cog and into the spokes of the wheel.
Step 5: The final step is to view the relationship of the guide pulley to the larger cog. This is where the B-tension screw comes into play. There should be a 5–10mm gap for most Shimano rear derailleurs and a 6–8mm gap for some SRAM derailleurs between the guide pulley and the cog. This is known as the B-gap. The SRAM 12-speed derailleur we are adjusting has a 15mm B-gap. SRAM does include a handy plastic guide for the proper spacing, but that might not always be on hand. Keep in mind that the derailleur/chain will change when riding on a full-suspension bike. Make sure to measure the B-gap if you have rear suspension with the shock at 30 percent sag to achieve the proper tension on the derailleur. If needed for your specific derailleur, adjust the B-gap by turning the B-tension screw to its recommended spot.
If you do need to make significant changes to the B-tension, double-check the indexing to make sure the chain is moving smoothly through all the cogs. Now, do some laps in the parking lot and adjust the cable tension with the barrel adjusters as needed. This will help you finalize your setup. That’s a wrap! You are done, and your derailleur should now be properly adjusted for the trails.
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