Ask a Mechanic: Getting Consistent Rear Shifting Across the Full Gear Range

Welcome to our Ask a Mechanic column where our expert mechanic Daniel Slusser answers your bike maintenance questions. If you have a question for Daniel, please post it on our Facebook Wall or e-mail Daniel directly at daniel.slusser@artscyclery.com. 
Question: I am able to somewhat tune the shifting while on the big ring, but the shifting does not sound very good on the small ring, and if I tune the shifting on the small ring, it messes up on the big ring. Any tips you have would be helpful. From: YouTube

Rear Derailleur Labelled

Because the cage pivot is offset from the upper jockey pulley, a misaligned derailleur hanger will change a derailleur’s shifting accuracy depending on which chainring is selected.

Answer: The problem you are experiencing is not unique to Di2 rear derailleurs and occurs on mechanical systems too. I believe your problem is likely the result of a bent derailleur hanger. If your derailleur hanger alignment is off, the upper jockey pulley will move out of alignment as the lower pulley moves toward the front of the bike when you are in the big ring and vice versa.

The next thing to check is your b-tension adjustment (screw at the back of derailleur nearest the hanger). Set the b-tension adjustment when you are in the lowest possible gear (small chainring, big cog) so the upper jockey pulley is as close as possible to the large cog without the derailleur bouncing off the cog as the teeth push down on the derailleur. Once the b-tension adjustment is properly set in in this gear, it will be set up correctly for all the other gears in the range.

Daniel Slusser is a professional bicycle mechanic with over ten years of experience. He holds a bachelor’s degree in business administration from HSU and a master’s degree in history from Cal Poly. When he is not riding, wrenching, or writing he enjoys spending time with his wife and two children.

2014-03-05T15:30:16-08:00