Tech & Wearables

Technical FAQ: Troubleshooting rear derailleur issues, alleviating wrist pain

VeloNews' technical expert talks about drivetrain alignment and more about how to diminish wrist pain when riding.

Have a question for Lennard? Please email him at veloqna@comcast.net to be included in Technical FAQ.

Dear Lennard,
I am running Shimano Dura-Ace 9170 on my Pinarello Dogma F8. The rear derailleur will not engage the smallest cog.

I have done multiple things to troubleshoot. I have confirmed that the derailleur hanger is straight using the Park Tool DAG-2.2 alignment tool. I have replaced the chain and cassette. I have swapped in a substitute Ultegra Di2 derailleur, which does work.

I finally located the problem: The derailleur simply is not shifting outward far enough. In fact, the outer limit screw is not engaging the derailleur at all.

Is there a way to fix this, short of replacing the (very expensive) Di2 rear derailleur?
— Rich

Dear Rich,
If I were you, I would try putting a washer between the derailleur and the derailleur hanger to shim it out a bit. Repositioning it laterally like that might line it up under the smallest cog. You’d then simply readjust the derailleur position to line up under each cog, let the lower limit screw out a bit, and you could be in business. Since that Ultegra Di2 derailleur works, your drivetrain alignment is otherwise probably fine.
― Lennard

Dear Lennard,
I have a question regarding the derailleur jockey wheels. When it comes time to replace them, how important is it to find the OEM replacement for the specific derailleur? With the vast variety of manufacturers, as well as different models within a manufacturer’s range, it is sometimes difficult to find the exact replacement. This is further complicated by the proliferation of inexpensive, off-brand replacement pulleys. For example, I have a 10-speed Shimano XTR rear derailleur on my mountain bike. I have replaced the pulleys twice on it over the years. The first time I used some generic aluminum jockey wheels. They seemed to work fine, albeit a little noisy (and the bearings weren’t sealed well, so they didn’t last very long). The second replacement set was an unknown Shimano variety that had been hanging around my garage, but most likely an Ultegra set. These jockey wheels seemed to work fine and there was no degradation of shifting quality. And now, it’s time to replace them again and I have found a set of OEM replacement pulleys, but at a cost that is at least twice other Shimano models, and three times as high as off-brand units. Is there an advantage to going with the OEM part, or is just using anything that fits good enough?
— Trent

Dear Trent,
Matching the number of teeth on the replacement jockey wheel and its width when installed in the cage to the old jockey wheel will ensure that it will work. Better bearings (or bushings) and different materials are simply icing on the cake and will reduce friction and perhaps improve longevity and gee-whiz factor.
― Lennard

The larger pulley wheels on this after-market rear derailleur modification increase the radius of the chain’s bend, thus reducing drivetrain friction. Photo: Logan VonBokel | VeloNews.com

Dear Lennard,
I started thinking about the focus on chain line friction and that led me to think about something that I have yet to see being discussed. When installing a new chain, the typical methodology for establishing the correct chain length seems to be pretty vague. Vertically aligning the rear derailleur pulleys while holding the two ends of the chain just seems really flawed, especially in a realm where we are now being informed of one-watt variances. Surely having a chain that is a link or two too long or short could have a measurable effect on friction. I didn’t say relevant, because I personally don’t think one or two watts is relevant to the vast majority of cyclists, but that’s a different topic. Maybe there is an opportunity to develop a tool that attaches to a rear derailleur that would at least make the alignment measurable instead of eyeballing it? Your thoughts?
— Scott S.

Dear Scott,
While current methodology for determining chain length actually is more like wrapping the chain around the largest chainring and largest cog (without going through either derailleur) and adding a whole link (inner + outer) or two (with variations depending on 2X or 1X, rear suspension length changes with sag, etc.), your point is still taken. However, since the majority of the friction due to the chain happens on the top span of the chain, where the tension is far higher than in the bottom span, I don’t know that it would make as much difference as you think to run a long chain. And with today’s longer jockey-wheel cages, more setback to the rear derailleurs, and much wider ranges of rear cog sizes that they are asked to shift across, adding even a link or two can result in the chain going around the upper jockey wheel bumping on the chain span between the lower jockey wheel and the bottom of the chainring when cross-chaining from the inner chainring.
― Lennard

This Redshift stem has elastomer pads to allow slight flex and suspension over bumpy terrain. Photo: Brad Kaminski | VeloNews.com

Dear Lennard,
You wrote about a rider’s wrist pain from arthritis or other conditions in your November 24 column.

I have arthritis in both wrists, and they would get sore from the pounding on longer rides on my road bike, which is pretty stiff. I saw an ad for a Redshift Sports ShockStop suspension stem — I think it was a discount offer at the time. I decided to try it and over time the pain has nearly disappeared. These use two internal elastomers to regulate the amount of give and so can be tuned to weight and preference. It’s a little heavy, but I’m not racing, so the weight is not a big deal. I recently saw an ad for a new version which is billed as lighter than the original. Mine’s the same length as the rigid stem it replaces. I’m also a guitarist, so the reduction in pain really helped my playing as well.
— Larry


Lennard Zinn, our longtime technical writer, joined VeloNews in 1987. He is also a custom frame builder (www.zinncycles.com) and purveyor of non-custom huge bikes (bikeclydesdale.com), a former U.S. national team rider, co-author of “The Haywire Heart,” and author of many bicycle books including “Zinn and the Art of Road Bike Maintenance,” “DVD, as well as “Zinn and the Art of Triathlon Bikes” and “Zinn’s Cycling Primer: Maintenance Tips and Skill Building for Cyclists.” He holds a bachelor’s in physics from Colorado College.

Follow @lennardzinn on Twitter.