Are there any road bike electronic shifting systems out there currently that only have a single up and down shifter lever and use a computer to make the decision of whether to shift on the rear cassette or the front chainring for you, instead of you having to make that decision yourself? I've heard that some current systems might have failsafes to try to prevent cross-chaining, but as far as I know, these still have the ability for the user to decide for themselves between the front and rear, whereas I am looking for a totally computerized system, where the user is not presented with this choice. If this does not exist yet, is it in the works somewhere? What do you think is the timeframe on such a thing coming to market? What has prevented its inception so far?
SRAM eTap has a mode for this. It’s called Sequential Shift Mode:
Sequential Shift Mode simplifies the shifting experience by automatically controlling the front and rear derailleur as you upshift or downshift through the gearing range. Using only the left or right shifter buttons, the system controls the shift behavior of both derailleurs to keep the changes in gear ratio smooth and cadence consistent. Pressing one controller makes the gearing easier, the other harder, it’s that simple.
The Shimano di2 system does this if you want. Using their app you can program the buttons to sequential shift 2, which I am using. You can choose where the computer shifts the front chainring and how much it shifts the rear to compensate for the larger shift in the front. I have my right buttons configured this way and the left buttons configured just to shift the front, which is useful when I am coming to a climb. I would rather shift the chainring before the climb rather than on it.
That would be a terrible idea.
Front shifts are slow, especially if you have large difference between the chainring sizes (like you usually do).
Rear shifts are fast, especially if the cassette is a hyperglide cassette (or some of the newer equivalent types of technology).
The beauty of the current user interface is that you have the ability to decide if you need your shift to be fast, or if it's acceptable for the shift to be slow, by having two shifters you can operate independently.
If there's only one shifter and the computer automatically decides whether to shift front, rear or both at the same time, it may mean you get a slow shift when you absolutely want your shift to be fast.