Technical FAQ: 12-speed Di2 hydraulic levers with 11-speed derailleurs, Campy Chorus chainring swap, DVT, Gates belt portability

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Dear Lennard,

A friend’s Dura-Ace Di2 rear derailleur gave up the ghost recently, although in fairness, it was about 8 years old and had seen a lot of use. That prompted me to go ahead and buy myself a spare Ultegra Di2 rear derailleur, since I have two bikes that are compatible, and since the derailleur was relatively cheap ($240).

But that got me thinking of shift levers. Two in my tribe have had 11-speed flat mount hydraulic levers fail, both under warranty (leaking). The most recent had to wait quite a while to get a replacement set. That got me wondering if I should own a spare set, or if that’s silly. My one thought was that it was possible that a 12-speed lever might work with my 11-speed derailleurs, as I recollect 11-speed levers were compatible with the original 10-speed Di2, since the brains of the outfit is not the shift levers.

Any idea if that’s true — if in a pinch I could use 12-speed hydraulic levers with 11-speed derailleurs? And along those lines, are there any compatibility issues between my old R785 brakes (painted over XT), 11-speed flat mount, and 12-speed flat mount?

― Steve

Dear Steve,

No, you can’t run 12-speed Di2 hydraulic levers with 11-speed Di2 derailleurs, because the e-tube wires are completely different. The 12-speed wires are much thinner and won’t snap into the same ports. The whole system is different; as it is wireless from the levers, there is no Junction A that wires from the levers plug into, for instance.

I’m also a bit curious about your statement that you could run 11-speed Di2 hydraulic levers with 10-speed Di2 derailleurs. My memory is not the steel trap (or even titanium trap) it once was, so I’m trying to recall if there was a time when there were 10-speed Di2 systems that used the same e-tube wires as 11-speed does. Certainly the wires on first-generation 10-speed Di2 were different and incompatible with 11-speed e-tube wires. If memory serves, original 10-speed Di2 were two-conductor, and 11-speed ones are single conductor.

BTW, we’ve run into that leakage issue with some 11-speed Di2 levers when we’re assembling new bikes. The fix was relatively easy — we replaced the reservoir cover.

― Lennard

Also read: Technical FAQ: Anticoagulants, 12s Campagnolo cranks on 11s drivetrain

Dear Lennard,

With a Chorus 12-speed 11-32 cassette, I find I don’t need the small 34-tooth chainring. Would the chainring shifting be pretty similar if I change it to a 36-tooth with my 50-tooth chainring to provide a little more overlap between my chainrings? Everyone says chainrings today have to be “matched” but not sure how much difference it really makes.

– Christian

Dear Christian,

In my experience on similar drivetrains — albeit not on your particular combination — I think you can expect it to work just fine. Yes, chain pick-up teeth on paired chainrings are oriented to be lined up with each other to enhance shifting speed and smoothness. Still, I find that most people shift up with their foot at the top to the crank circle, and the chain ramp on the big ring will be there to receive the chain no matter what size chainring is inboard of it.

In any case, it will shift. Even if the shift is slightly less smooth, I’m guessing that achieving your goal of having the gear combinations you want will override any decrease in shifting efficiency.

― Lennard

Dear Lennard,

I’d like to comment on the October 25th question from Mike regarding hypercoagulability and resting heart rate. I’m an MD but present myself here as an amateur exercise physiologist, as it’s not my field of expertise.

I don’t think Mike’s concern about a low resting heart rate plays any role in deep venous thrombosis (DVT) formation.

As you know there are many complex factors involved in abnormal venous clot formation, and the accepted theory for clot formation requires one or more conditions: abnormal lining of the blood vessel wall, abnormality in the blood itself, or abnormal flow with excessive stasis or turbulence. The combination of these three conditions is called Virchow’s Triad. A low heart rate does not factor into this. Mike may be associating sleep’s low resting heart rate as a risk for young cyclists dying in the 1990s, but these riders were usually found to be taking EPO and had abnormally high hematocrits — a risk seen in Virchow’s Triad. Mike’s medical issue is that he probably suffers from a hypercoagulable state, a risk seen in the Triad above. The Xaralto offsets this problem. He could have his exact issue evaluated further if he’s interested.

Also, if one is concerned about venous flow, low resting blood pressure would theoretically be more likely to trigger a clot than rate, but this does not seem to be the case. Note that the venous stasis is required for clot formation, so obstructed venous flow is the risk here. Venous flow is a low pressure system, and flow is augmented by muscle contraction or external compression. Like you, Mike could wear compression stockings or flex his calves several times a night, as the popliteal vein (behind the knee) is a common place for clot formation. Again, low venous flow from low heart rate and low BP doesn’t equal venous stasis. A car engine at idle with an oil pressure of 15psi and 800 RPM isn’t more likely to form an oil galley blockage versus an oil pressure of 50 psi at 4k RPM.

Note also that Mike’s proposed target resting rate of 50 doesn’t seem statistically different from 40 if his range is 40-175 BPM. I don’t think the platelets recognize the 6% rate difference on the low end of the range.

If I were him I would enjoy the great outdoors and not worry about having Miguel Induráin-type resting rate. Stay hydrated, and think of the resulting 3 a.m. pee as an opportunity to improve venous blood flow. He should probably pick up a copy of the “Haywire Heart” to make sure he’s following heart- healthy guidelines (not a shameless plug!). He should also have regular blood panels to ensure that he’s not polycythemic (he won’t be unless he develops an unrelated blood disorder).

– Michael

Dear Lennard,

I rode Gates belts on singlespeeds for a bit a decade ago. I was able to stick a coiled belt in my jersey pocket. FYI. Thanks for the great column.

– Jeff

Lennard Zinn, our longtime technical writer, joined VeloNews in 1987. He is also a custom frame builder and purveyor of non-custom huge bikes , 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