By Simon Paterson, Bookhouse, Sydney
What simon does when he isn't typesetting...
A look at the potential future for electronic groupset gear shifting components such as Shimano's Di2.
The release of Shimano's electronic groupset, Di2, into the hands of the cycling public triggered some logical analysis of the future of this technology. Indeed, some of the the desires for my own cycling experience could now be realised.
Seemingly the logical next step is to interface a cyclocomputer with the brains of the electronic shifters to start to control the behaviour or receive feedback from the system. This relatively minor technological feat opens the door to many possibilities.
I've often had a desire to know which gear I'm in while on my training rides. I use my gear and cadence settings as a basis for my workout intensity on the rollers. Given that the brain of the electronic shifting system would be aware of the gear in use, it seems a relatively minor technological step to announce the setting via an ANT+ link which could then be displayed on any ANT+ compatible computer.
One of the first things that came to mind was the concept of automatic shifting. I envisaged this would be based on cadence, since I tend to aim for a fairly consistent cadence when I'm riding. Naturally, if you like riding between 90 and 100 RPM, then surely a change in this cadence outside this band of values could trigger a change in gear. Of course, there would need to be some so-called ‘fuzzy logic’ or ‘artificial intelligence’ (two terms I'm not fond of) applied to the algorithm; you wouldn't want to change to your lowest gear if you were just stopping a traffic lights. You'd also want to apply some hysteresis, ignoring any temporary movements outside the band. A comment on a blog post also noted that this automatic shifting could be based on wattage output. Regardless of the mechanism, it would be an interesting system with which to experiment.
This is perhaps the area I have put most thought into. Cross chaining is discouraged by drivetrain manufacturers and creates an uncomfortable noise for the rider, not to mention additional unwanted wear on the components. Sequential shifting would allow us to avoid cross chaining altogether.
The standard way of analysing gear ratios is ‘gear inches’, a relative number based on chainring and cassette tooth count. There are several calculators available on the web, such as Campagnolo's gear inch calculator. If you dial in your sprocket settings you will get a table of numbers with the gear inch settings for each gear. Here is an example:
| Gear-inch | |||
| Chainring teeth | |||
|---|---|---|---|
| Cassette teeth | 39 | 52 | |
| 12 | 6.81 | 9.08 | |
| 13 | 6.29 | 8.38 | |
| 14 | 5.84 | 7.79 | |
| 15 | 5.45 | 7.27 | |
| 16 | 5.11 | 6.81 | |
| 17 | 4.81 | 6.41 | |
| 19 | 4.30 | 5.74 | |
| 21 | 3.89 | 5.19 | |
| 23 | 3.55 | 4.74 | |
| 25 | 3.27 | 4.36 | |
| Wheel Circumference: 2096 mm | |||
If you look at these numbers you can see that there is a fair amount of overlap between gears accessed from the inner and outer front chainrings. For instance, the gear inch setting of 6.81 with the 39 front and 12 rear cross-chain combination can easily be substituted by using a 52 front and 16 rear setting. Why use a cross-chain combination when a better combination exists? Often the reason is that the number of shifts required to avoid the combination may take the rider some time to calculate and execute, or simply that the rider was unaware they were about to engage the combination. With electronic shifting, it should be easy to avoid these combinations altogether.
If you examine the gear inch table for any chainring/cassette combination you can easily chart a linear gear inch sequence. It is interesting to note in this example that this sequence would require movement of both the front and rear derailleur with virtually every gear change. For example, the sequence might be like:
As you can see, you may be moving from the inside front chainring to the outside between one sequential gear and the next. Although this kind of sequential shifting would be possible with an electronic groupset, it may not be desirable, regardless of the smoothness and reliability of the shifting. Nonetheless, if this was desired, it would merely facilitate a 'mode' of shifting on the electronic groupset brains (or using our cyclocomputer which is now interfacing with the groupset). The small incremental steps offered by this pure sequential shifting are probably not required. It would be useful enough to simply be able to avoid cross chaining.
A sequential shifting system would involve only two buttons: up and down. When the gears approach the cross-chain combinations they simply select the next combination on the alternate chainring. Only at this point—in either up or down shifting—would both the front and rear move in the same shift. In all other situations, a shift up or down would require movement of only the rear derailleur. So, instead of shifting from 39/13 to the cross-chain combination of 39/12 for a gear inch of 6.81, the computer could do a sequential shift to 52/16 giving us the same gear inch setting; requiring three rear up-shifts and a move from the inner to outer front chainring—a simple operation for the electronic shifters. (Or, the computer could shift us to 52/17 for a gear inch of 6.41, a smaller incremental step.) Regardless of the mode the user decides on, it is clear that sequential shifting is a practical system which can be easily implemented using electronic shifters; the rider does not need to worry about the position of the front and rear derailleur but rather concentrates on merely needing to shift higher or lower—like a car—depending on speed and terrain. This may introduce the desire to make multiple shifts in one step.
The concept of sequential shifting—thereby reducing the shifting interface to only two buttons—opens up the possibility of keeping all four buttons but using them for different purposes. For example, what if we used the other two buttons to signify that we wanted to shift multiple steps? By holding one of the extra buttons while shifting up or down, for example, we may get two sequential gear shifts. By holding the other button while shifting, we get three steps. Holding both, four steps; or some other pre-programmed number of steps, perhaps five? Obviously, the combinations and step counts would be customisable. Another system may be to use the second set of buttons to engage two sequential shifts; if the rider wanted three shifts they use both buttons, either at the same time or close together. Five steps would be a double-click then single. The actual use of these buttons could be customisable.
In lower end groupsets, only two buttons would be available. Higher end groupsets may offer many exotic button placements and combinations. One button for lowest gear and another for highest? What if we hold the up-shift button for more than 1 second? We could program the computer to take us to the first gear on the large front chainring if we are on the inner chainring, or to the highest gear if we are already on the the largest chainring. Favourite gears—that special combination you love to use in your climbing breakaway? Preset combinations changed during the race using the cyclocomputer, depending on terrain? There will be many ways these buttons can be employed once we implement sequential shifting. Personally I like the idea of just simplifying the system to two buttons; lower gears on the left and higher gears on the right. Others will surely have more complex desires.
The cycling fraternity may be slow to embrace these ideas; in the heat of a race simplicity can be most beneficial. Simple up and down will be basic, with other exotic combinations slower to emerge. In essence, though, once the interface between computer and gear system is created, it will be a small technological step to put the customisation of these buttons entirely in the hands of the user. We have four buttons now; two on each shifter. Everybody is used to them, whether analog or electronic. In the digital world, the purpose of these buttons is merely a detail.
For the traditional, things can stay as they are with the current version of Di2. For the adventurous, demanding or just plain geeky, the interface between the groupset brain and the computer will offer irresistible temptation. The more I think about it, the more I begin to believe that the current system of selecting gears by changing cogs is obsolete. Sequential shifting is fair more logical.
Perhaps less interesting for pro riders is the idea of shifting to any specific gear by simply selecting it on a touchscreen interface on the cyclocomputer. Want the 52/14 combination? Just tap the screen. Certainly an easy technological feat to achieve, but pro riders will surely be unlikely to embrace such a feature. I imagine the demands of high-speed racing simply doesn't allow for such finite computer interaction.
It could also be possible to store and load different calibration settings for different wheels or bikes using a computer capable of interfacing with a PC. With an interface between the cyclocomputer and the Di2, the calibration settings determined by the Di2 while in adjustment mode could be sent and stored by the computer, even if that required that the computer be tethered to the PC during the process. However this was implemented, the ability to shift between wheels and Di2 calibrations would be useful.
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