There’s a common sentiment in the touring/bikepacking/bikecamping world when it comes to gear selection that seems to be to pick simple things over complex ones. Choose parts that are easily serviceable in the field. That way when they break, you can fix them. This is why you’ll hear people sticking with cable-actuated brakes over hydraulic; because they fear their brake failing on a ride and don’t want/know how to bleed hydraulic brakes either on the side of a road or in the woods.
This same mindset sends people running for the hills when they think about electronic drivetrains. Some people shy away from them for standard road riding, so it’s no surprise that the touring crowd is averse.
I choose to be adventurous when going on adventures. A year ago I swapped out the stock setup on my Salsa Fargo with SRAM hydraulic disc brakes. Let me preface this by saying, they work great. I did, however, fail to notice that Salsa’s frame spec doesn’t allow for a 140mm rotor in the rear. If you put such a rotor on one of their frames (with Alternator dropouts), the caliper, it turns out, will not be able to position properly and after a few rides, the inboard piston will be pressed out far enough to burp the seal and air will get into the system, the brake will cease to function. I didn’t realize this initially so after several fail cycles, I decided it was time for different brakes.
There were two ways I could go: I could put the cable-actuated hoods back on and go with something like the TRP HY/RD brakes; or I could go with Shimano hydraulics. I chose Shimano because I’ve known their hydraulic systems to be the most reliable, best feeling, easiest to service in the industry.
The problem I now faced was that I had a bike with drop bars, so I’d need road-style brake levers, no problem. But I would want a drivetrain that could handle a large range cassette (40-42T) and rough trails with no front derailleur/chain keeper (i.e. I’d need a mountain derailleur with a clutch mechanism). Unlike SRAM, Shimano’s road and mountain drivetrain lines are not interchangeable†.
The solution: Shimano R785 di2 to XTR 9050.
These are top and second-tier Shimano parts so suffice it to say they are of impeccable quality. As such this is not a review of them. This is a review of using an electronic shifting system, specifically Shimano’s Di2 for long range, off-road bikepacking.
I run Shimano R785 (XT quality) controls and brakes, an XTR-9050 rear mech, the BTR2 battery with BTC1 external case, and of course a 3 port A-junction. I mounted the battery just behind my Anything Cage on my fork, since it would have been in the way of my framebag and I didn’t have internal routing options. This works well, but requires a very long cable to get to the rear mech. The A-junction box also has to go somewhere (typically the stem), so if you’re cockpit is crowded (as a lot of bikepacking rigs tend to be) you might have to get creative.
What a mess
Here’s a shot of the bike. You can spot (maybe) the battery between the water bottle cage and Anything Cage on the fork leg. I ran the eTube down along the dynamo line, wrapping them together for security.
I’ve put over 1,000 miles on this drivetrain to date; many of that over rough, unpaved terrain. I’ve crashed several times. I’ve only had a single incident (300 miles into the TNGA) where the eTube (that’s what Shimano calls the wires) at the rear mech came loose. The solution was to push the tube back in “until it goes click“.
While I’m on the topic of the lone failure, I’d like to talk about modalities of failure.
With a traditional, sprung, cable-actuated drivetrain, if the cable going to the derailleur fails, the spring of the derailleur pulls it down into the smallest cog. In the case of the rear, this means upshifting into top gear; in the case of the front, it means downshifting into ‘granny’ gear. When an eTube fails, everything stays where it currently is. There’s no sudden shift that grinds you to a halt on a climb or violently jerks your knee into the handlebar. Nothing happens. You keep riding in that gear.
In both cases, if a cable truly breaks (and not just comes loose) you will have to have a replacement with you, so there’s no advantage (packwise) to one over the other. Just the difference in failure modality.
Moving on from failure to abuse, let’s talk about crashing.
With a typical dropbar setup, if you crash, the hoods are likely to have been twisted/skewed in some way. (Heck, you don’t even have to crash, you could just have a ever so slightly loose clamp which allows the hoods to shift while riding over rough terrain or pulling hard during steep climbs). With cable systems, which rely on precise lengths of cable pull, these hood movements could throw the shifting system completely out of alignment. With di2, you leave a little bend in the eTube just as it comes out of the hood which prevents the wire from being pulled out. That is all. The signal from the shifter to the derailleur doesn’t care how far it travels. It doesn’t care if you route it through a junction box, to another junction box, it doesn’t care how sharp it’s bent or whatever. As long as the system is clicked together, it shifts the same amount every time you press the button for a shift, and never when you don’t.
So what about that loss of power?
Well, we’ve already seen that if an eTube gets pulled out, that component is effectively removed from the system. If the wire to the battery were to fail/disconnect or the battery were to run down, shifting would just stop (a very expensive singlespeed). So how long does the battery last? Well that depends. If you have one of the gear display LCDs, it will probably eat some power and shorten life. If you have a front derailleur (in addition to the rear) you may experience shorter battery life. My experience has been that I was able to get around 750miles (with what I consider very frequent shifting) before the battery registered 50% charge (so maybe 1500 miles for anyone not savvy to do the math). For everything but the TourDivide or the TransAmericaTrail, you can probably get through with a single battery charge.
If you’re the “always be prepared” type though, the battery charger/PC interface for the BTR2 (SM-BCR2) connects to power/PC via microUSB, so you can use the same cache battery you’re charging your GPS/phone with to top up your battery (if you need to). If you’re considering Di2 for bikepacking you probably already have a dynamo, so worst case you could actually charge the system while riding.
As you may have noticed from the bike shot above, I use a 1x drivetrain. I’ve set up both shifters to control the rear mech. I did this for redundancy (if a shifter failed I’d still be able to shift) but I’ve found it has some unintended consequences as well.
Update your derailleur firmware!
Since I can do both shifts (up and down) on either shifter, I can use the same button on either shifter to make it so that left-hand-shifts-up-right-hand-shifts-down (or vice versa) or I can just use the left hand to shift (not something typically possible on 1x drivetrains). Big deal you say? When you’re tired and trying to eat or drink something and suddenly need to shift… this is a big deal. Also, when you’re tired and looking for extra hand positions, but need to shift, and you don’t have to get all the way back to the standard shifting positions because you only have to just barely reach the edge of one of the buttons with the tip of one of your fingers… this is a big deal. Also, when you’re tired and your hands are aching, it’s really nice to only have to tap a button as opposed to move a lever, which pulls a cable, which fights a spring (No missed or halfshifts because you couldn’t make your hands commit.)… and that’s not even mentioning how nasty and gunked up your shifting cable housing might be by that point and the impact that has.
So I’ll mention shifter cable housing gunk now. It’s real. You can usually muscle through grimy cable situations, but the spring on your derailleur may not be so strong. You may find yourself, as I have, stuck towards the lower end of your cassette, unable to shift to bigger gearing as the trail finally starts to level out. ETubes are immune to such gunk. And an electromagnetic servo motor (which is how the di2 mechs move) has a bit more torque than that spring might impart on the cable system. Perfect shifts, every time.
Now that I’ve talked about my experiences with di2 and bikepacking, I would like to hypothesize about some of the potential issues which I have not experienced, but which may be of real concern to some.
Battery life. I mentioned my experience. Clearly #ymmv, but specifically in the case of cold weather touring. [All] Batteries are known suffer performance degradation when the temperatures plummet. I haven’t done any really cold weather riding with this setup so I can’t speak to how that might affect things, although I’d assume you’d need to charge the battery more often. I will also mention that I’m referring to cold and not freezing, and to riding temps, not camping temps. If it’s going to be super cold overnight, it’s probably worth it to take the battery out and bring it into your tent/bag. If you are riding in consistently freezing temps, you’ll run into drivetrain problems no matter what you have, and I’d also hope that you know what you’re doing and wouldn’t be looking for advice from me.
Parts availability. Di2 is becoming less fringe as it trickles into lower tiers, but you will still be harder pressed to walk into any old bike shop and be able to purchase a spare eTube or component from stock than you would a standard cable etc.
Shift flexibility. I mentioned my shifting arrangement with two shifters controlling one mech. But Shimano has programmable shift mapping which allows you to run a 2x or 3x drivetrain (i.e. two mechs) with just a single shifter. You do this by programming your shift progressions into the firmware via the eTube software. I don’t have a front mech so I can’t play around with this, but I would be interested to know if you can mirror that same shift functionality to a second shifter. That is, could I have the same redundancy I currently have with a 2x drivetrain? I just don’t