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 firstname.lastname@example.org. Today’s column offers some tips on Shimano Di2 front derailleur tuning in response to the video below on the Art’s Cyclery YouTube Channel. The second question covers how to troubleshoot suspension forks that fail to get full travel.Question: Great informative video on you tube. When aligning a Di2 front derailleur does it matter what gear the rear is in (because of trimming)? From: George
Answer: It doesn’t matter what gear the rear derailleur is in when aligning the front derailleur because trim won’t affect alignment. I prefer to have the front derailleur shifted into the small ring and then adjust it so that the outside of the cage is parallel with the big ring.
Question: I have a question about my 2010 Rock Shox 150mm Air u Turn Revelation. I bought this about 4 months ago slapped it onto my Lapierre Zesty 2011 (I know its a little more travel than the stock) and I cannot seem to get all the travel needed.
I weigh in at 77Kg fully loaded. Fork travel is at 150mm with 45psi in the positive air spring chamber and 55psi in the negative chamber. Even with some small drops I cannot seem to get more than approx 11-12cm Travel!! Question: If I was to swap the “u-turn air spring assembly” for a regular “dual air spring assembly” would this help give me more travel? I feel like I shouldn’t go any lower than 75PSI in the air spring, but I had to come down as the fork gave me hardly any travel. Do you have any tips on how to make the most out of this great trail fork? From: Shaun
Answer: The standard Dual-Air spring assembly will get you a little more usable travel than you are seeing with the air u turn unit. But before you buy a new air spring assembly, check to make sure you have the correct amount of oil in the lowers. If your rebound damper seal head is leaking or the former owner of the fork put too much lubrication oil in the lowers, travel can be limited. Your fork only requires 5ml of 15 weight fork oil in each leg. That’s about one 9th of the volume of a typical shot of liquor, or about a teaspoon’s worth.
Here is a tuning tip for Dual Air forks: Use less negative air pressure to get more travel at the end of the stroke without having excessive sag. Another option to pursue if you have the Black Box compression damper, RT3 compression damper, or one of the other dampers with external blowoff threshold adjustment, is to turn on the low-speed compression damping (some people mistakenly think this is merely a lockout) and set your blow-off threshold very low. Usually 0-2 clicks is all you need. This will keep the fork riding higher in the travel, resisting dive under braking and cornering while allowing you to use less air pressure so that you will get more travel on bigger hits.
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.