Technical FAQ: Synchro shift for wide gear range; more on skin sensitivity

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

Dear Lennard,
I have a method for increasing the range of gearing on road bikes that I have not seen mentioned, although there has been a lot said about various ways of doing that and I may have just missed it.

One can take advantage of the fact that Synchro Shift limits cross-chaining to run a much larger gear range on Di2 derailleurs without exceeding their capacity.

For example, I have a 9-46 cassette, but I set the Synchro Shift to limit the rear to <= 28 while I’m on the big chainring in front, and >= 17 when I am on the small chainring. I run 53/34 in front, so the derailleur only has to take up the slack between (53×28) and (34×17), for a difference of 30. That is three less than Dura-Ace’s maximum capacity. Of course, I size my chain only to accommodate the 53×28 combination (committing me to Synchro Shift), and I use a road-link [extended derailleur hanger] to drop the rear derailleur down to make room for the big cogs. The difference between gears is about 15 percent, compared to 10 percent for the standard configurations.

I have a total of about 7,000 miles over three years on that arrangement. It works well for me. Note that the combination of lowered derailleur from the road-link, B-screw setting to clear the big cog, and the small diameter of the 9 and 10 tooth cogs means that only about three teeth are engaged on those cogs. I have wondered if that might allow the chain to skip if a rider tries to stomp hard on those gears, but I haven’t tried that. I have also wondered if SRAM has an option like Synchro Shift because then one might be able to take advantage of the fact that they allow you to mix road and mountain to use a rear derailleur that is designed to work on big-range cassettes.

I designed the above configuration to let me climb greater than 10 percent grades at close to my normal average power of about 150 Watts. The way it works of course is that the lower ratios allow me to keep my cadence up at low speeds, say 5 mph (8 kph). Being able to keep my cadence near 60 maintains stability and reduces the torque my legs have to apply to provide the power. If you think about the experience of struggling with a climb, it is a cadence dropping below 50 and insufficient strength.

My experience with low gearing has been that being able to moderate my exertion on the steep climbs makes long rides much more enjoyable and faster overall, and I don’t seem to notice the bigger difference between gears. Judging by the power numbers I see in Strava, I think most riders would benefit from lower gearings than are currently standard. That is not surprising, since the current standards are essentially what the pros use, and they average more than twice the power that most of us sustain.
— Matt

Dear Matt,
That is an excellent way to get a super-wide gear range. The danger is that you could rip your expensive Di2 derailleur apart by shifting with that short chain to the big chainring when beyond the 28T cog.

Shimano Synchro Shift shifts both the front and rear derailleur by asking for an easier or harder gear only with the rear shifter. Thing is, having Synchro Shift selected in the Di2 system doesn’t prevent shifting the front derailleur with the front shifter, and that’s how you can rip the rear derailleur apart, by shifting to the big chainring with the front shifter when the chain is on one of the cogs that’s larger than the 28-tooth. Clearly, this is not a bike that you want to let anybody else ride, because they unknowingly could shift the front shifter to the wrong gear combination.

You could prevent this from ever happening by disconnecting the e-tube wire from the left shifter. (I say the left shifter when meaning the front shifter because that is the standard setup, but the Di2 e-tube software allows you to designate the right shifter as the front shifter instead. In any case, the point is to disconnect the wire from the front shifter.) Then there is no other choice than to do all shifting from the rear shifter, and you will only select allowable gears for the chain length.

By increasing the distance from the upper jockey wheel to the cog, the RoadLink will decrease the amount of chain wrap on the smaller cogs, so chain skipping is more of a likelihood. That’s partially balanced by the fact that the chain tension is lower on the larger chainring than when on the inner chainring. It sounds like you never have an issue with it. It’s probably a good idea to avoid sprinting in your highest gear. Chain skipping when standing on the pedals at high speed can be disastrous.
― Lennard

More suggestions for resolving skin sensitivity to stretch fabrics:

Dear Lennard,
My wife is a dermatologist and recommends fragrance-free and dye-free laundry detergent and bath soap to all of her patients. They are a common cause of contact dermatitis, even in people who have not previously had an issue with them. As a bonus, going dye- and perfume-free is better for the environment.
— Randy

Dear Lennard,
A couple of years ago, I had a serious rash on my inner thighs. Initially, it was really puzzling because I hadn’t been wearing new bib shorts. Although it was a hot, humid period during summertime, the weather wasn’t anything out of the ordinary for our area. I finally figured out that we had started using those new laundry pods in place of our usual liquid detergent. After washing my cycling clothes in liquid again (and setting the machine to run a second rinse), my problem was solved.
— Kevin

Dear Lennard,
Just to add a word to the discussion about allergic reactions to chamois and lycras: for several years I wore a Road ID band on my wrist 24/7. One day my wrist broke out in a vicious rash. I asked my dermatologist why this waited years to happen, and he said, That’s how allergic reactions work—you go along without a problem for X amount of time, then bam, you break out. This can happen with any substance you keep next to your skin for an extended time. He told me of a patient who wore the same perfume daily for 20 years, then suddenly became highly sensitive to it. So often the simplest — or only — solution to skin sensitivity is to switch to any other substance.
— Jack

Dear Lennard,
I went through a phase where I thought I had an allergy. Here is what I changed in my wash routine and have never had an issue since.

Cold water
Hang dry
Tide Free and Gentle…no perfumes
Clorox Laundry Sanitizer
Wash after every ride
Wash separate from other laundry
I also never “hang out” in cycling gear after a ride. That’s just gross. If I cannot get a shower within 30 minutes of ending a ride, I at least get out of the gear and use some baby wipes or Chamois Butt’r skin wash.

— Geoffrey

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.