Moving in Stereo, Part II

Moving in Stereo, Part II

For Part I, click here.

Driving the bus
Not all tandem experiences are created equal. I once rode a tandem that felt like I was unintentionally courting disaster. (Shepard notes that when Co-Motion started in 1988 their top tubes were 28.6mm in diameter, not the 44.5mm of this bike.) I rode another that was as averse to turning as a school bus. Some feel longer than they actually are. Co-Motion has earned a reputation for some of the best, if not the best handling bikes out there. What this comes down to is how much of the time you’re steering the bike rather than countersteering the bike. Once you’re above about 14 mph on most singles, your direction control comes through countersteering. The longer a bike’s wheelbase, the higher the speed you must go before you countersteer. The upshot is that often when at speeds where you’d expect to countersteer (e.g. 18 mph), you still need to steer most tandems.

Co-Motion offers the Periscope Torpedo in three stock sizes; we went with the medium, which has a 56.5cm effective top tube. Both seat tubes are 73 degrees. The head tube is 73 degrees and is paired with a 50mm-rake fork for 5.17cm of trail; that would be crazy quick for a single, but this is part of what makes the Torpedo handle more like a bike and less like a semi. The long wheelbase offsets the short trail. Bottom bracket drop is only 72mm, but that’s because dropping it more than that makes pedal strikes in turns much more likely.

This bike was, in part, a chance to ask the question, what’s the best way to build a tandem today? Though some options, like triples, have been all but eliminated, there are still a number of gearing options, and as I’ve written elsewhere, a 50×11 is a big gear. You’ve got to be seeking maximum warp to conclude you’re undergeared with that. The bigger problem is finding a gear low enough for the hills. I went with an 11-32 cassette, which gives us a 34×32 low gear—nearly a 1:1 ratio. I think on long climbs this could still be a problem, but until we tackle the Geysers or Coleman Valley, I think we’ll be okay. What we’ve lost in gear range the addition of Di2 electronic shifting has overcome with a near miracle. Tandem shifting has been wonky enough that Di2’s performance advantage becomes that much more apparent.

I’m just going to say it: There’s not a better solution for tandem drivetrains that Shimano Ultegra Di2.

Instead of a traditional timing chain, we went with a Gates belt drive. The reasons why are pretty compelling. It’s quieter, lighter, requires no maintenance, won’t stretch and features lower drag. There’s no downside that I can find.

All these options—S&S couplers, Ultegra Di2 hydraulic, Gates belt drive, da Vinci cranks, specialty paint—adds up. So while the base model was only $3895, what you see here goes for closer to $8600. That’s a lot of dough, but I’ll argue that for the rider willing to make the investment, the satisfaction that comes from seeing the perfectly dialed bike makes the outlay worthwhile. There’s no real substitute for having your kid say, “Oh boy, we’re going to ride the tandem!”

As captain, I have trouble hearing a missed shift, and my stoker doesn’t know enough to be able to tell me when the bike has missed a shift or if I need to trim a derailleur. It’s best if we just leave him out of the feedback loop and go with shifting that will simply perform correctly, always. That’s what Di2 does. And one of Di2’s best and least-lauded features is its ability to shift perfectly when under load and at a low cadence. It’s low-cadence shifting that makes me most nervous. That’s most often when I’ve broken chains. But the Di2 is as flawless as the face of Grace Kelly.


It looks like what?
Without belaboring the obvious, a tandem is a big thing. A whole lot of bike. So any color you paint it is going to make a big statement. You’d better like that color a lot. There are a limited number of standard colors, but as I mentioned, for an upcharge you can go with something outside of the stocks. Co-Motion does all their paint in-house and they’ve got a crack team that can do complicated paint schemes in addition to terrific fades as well as simple, one-color finishes. They’ve got more color choice than most companies, so the problem is less finding something you like than narrowing down which of the things you like most. That was my problem.

I brought Mini-Shred back to my computer one night and asked him to look at the colors and tell me which he liked best. He pointed to an orange and a teal. Co-Motion offers, among their Special Efx schemes, a riff on the McLaren Gulf scheme with a mostly duck-egg blue and some orange stripes. I decided to use the orange where the blue is and then use the teal where the orange is. I was pretty blown away when I opened the box, but the way Mini-Shred’s eyes lit up when I showed it to him told me I’d made the right choice.


Does he like it?
Most of you reading this have known for far longer than I have that kids are as fickle as subatomic particles. You just never know what they are going to want to do from one day—one minute—to the next. I’m fortunate that most days when I ask him if he wants to ride the tandem he says yes. Of course, there are days when I don’t even bother to ask; I just tell him to get his helmet. Runs to school or day camp are far more enjoyable, and they carry with them the added benefit of getting him some exercise early in the day, but that’s the stuff of another post.

I’ve got to be honest and say that communication is a bit harder with Mini-Shred being more than a foot lower than he was previously. With the child stoker kit I could talk with him with relative ease. Now I have to yell a good bit more. Mostly I find myself telling him to wait until we get to a light. It’s not a big deal.

There’s another feature of the Gates belt drive that no one talks about and you can’t appreciate it or even apprehend it until you’re on the road. Thanks in part to the super immediate engagement of the belt, when Mini-Shred turns on the power, I have a finer, more instant appreciation in his increase in effort and that tunes me into his desire to go faster.

To give you a fix on the minimum height a person needs to stoke with the PeriScope setup, Mini-Shred is 45 inches tall (probably 44 when we first started riding this thing), just tall enough to ride most amusement park rides. I had to insert the seatpost fully and insert the telescoping seat tube completely as well. The saddle literally won’t go any lower. Literally.

I’ve yet to really attack any of the area’s descents on this bike. I’ve tried one quick drop on my own, but that’s not the same as having another body in back, even if he weighs less than a big bag of dog food. The big reason I haven’t tried anything challenging is simple: Mini-Shred is intimidated by the combination of steep hills and high speed. As it turns out, 30 on a false flat goes over better than 30 on a steep grade.


I’ve always liked riding tandems because of the way the experience differs from riding a single with a friend. When you share the work, share the same line, the same pedal stroke, the ride becomes intimate in a way that no other form of cycling can replicate. In riding with my son he learns things about cycling that he wouldn’t learn if he was riding a trail-a-bike, or on his own. Being on the back of a tandem teaches him about holding a line, keeping his cadence up and pedaling consistently. On his own bike, he’s apt to pedal a dozen strokes and then pause. Riding the tandem is teaching him to keep pedaling—no sudden stops, either. We can go farther, and go faster, which allows us to see more.

Compared to the other steel and aluminum tandems I’ve ridden, this thing is smoother than 100-year-old whiskey. It is by far the most comfortable tandem I’ve ridden, and that’s surprising considering that it rivals the stiffest tandems I’ve ridden for resisting torsional flex. It’s a bit like budgets and cocaine addiction—one is the enemy of the other.

The Torpedo is also easily the best-handling tandem I’ve ever ridden. Part of the great handling owes to the advantage the PeriScope offers by keeping the stoker’s center of gravity as low as possible. I mean, it also helps that my stoker weighs a whopping 46 lbs., but regardless, the Torpedo carves turns in a way no other tandem I’ve ridden does. The key to enjoying riding a tandem is for the captain not to feel the weight of the stoker with every little course correction.

Final thought: Teaching your kids to ride is the bomb, but sharing the riding with them is even better.

, , ,


  1. Sean Co

    This is a great write up. I’ve thought about a tandem for my little one who seems to be the same size as your guy. Would it be possible to use the new XT Di2 with Ultegra shifters to get you more range?

    1. Author

      As I understand it, yes you could do that, but while you’d gain range, gearing-wise, all your gains would be at the low end and you’d lose a great deal of high end, which might or might not be objectionable.

  2. brian ledford

    How low a gear is practical? a 34×32 is 3ish mph at 40 rpm (I think). Can you go much slower and meaningfully stay upright? And these as nonrhetorical questions by the way.

    1. Lyford

      Don’t know how it’d work on a tandem, but on my mountain bike my low is a 28×36. No problem staying upright.

    2. Author

      My ability to generate power at 40 rpm isn’t great. Mini-Shred’s ability to generate power at that cadence is nonexistent. That’s the trick with little legs; you have to keep the cadence up because a kid of that size is an aerobic engine; once we’re below about 80 rpm it’s all me.

  3. Rick

    Glad you’re enjoying the tandem experience, and CoMotion is a great choice. Dwan and CoMotion have come since from their days of building bikes in a decrepit garage on the wrong side of the tracks in Eugene. LOL

    Two points I’d like to propose:

    There is an elegant, and not at all obsolete method available to get excellent shifting on a tandem- bar end shifters set to friction mode. I know you’re probably thinking I’m a neo-luddite, but it works quite well with no drama at all and is supremely reliable. It does require the learning of “touch”, but what’s wrong with that? In a time when so much is done automagically for us it’s satisfying to do something that requires a subtle learned skill. As all cyclists riding derailleur bikes learned in the not so distant past. Of course, I’m not suggesting that you switch to friction shifting on you new high zoot bike, but rather just mentioning that there is another good option.

    Secondly, have fun on those descents, but do it circumspectly because you are responsible for the safety of two souls when you captain a tandem.

    1. David Gifford

      Somewhere between friction and DI2 lies the unplumbed depths of indexed bar ends. I was just commenting to my wife the other day, (with my daughter on her kid stoker) that I hadn’t adjusted our old 8 sp dura ace bar ends mated to the XTR derailer in over 10 years of riding. A positive clunk, every time, no trimming necessary. While digital shifting is undoubtedly easier to operate, it is a more complicated collection of machinery, and I would hope that current analog tech was still up to the task that used to be pretty simple.

  4. Dustin Gaddis

    Padraig – have you and MiniShred ridden with other people yet? I could see a small group ride with friends being a TON of fun once the kid is old enough. But I can also see it being scary as hell.

    1. Rick

      Good point. Tandems have a different “rhythm”. If you’re riding in a pace line on a single with other singles and the riders in front of you ease up on the pedals, you ease up too and slow down at the same relative rate. A tandem carries more momentum and slows down “slower”, so you might need to use brakes in the above situation. Singles just love to draft a tandem, but usually don’t like them in a rotation even if they are doing everything right. (Ask me how I know….)

    2. Author

      Haven’t done that yet. Mostly just because there’s not a lot of group riding here. I used to do group rides on my tandem, years ago when my stoker was experienced with group rides. We were able to take our pulls and only had trouble with big accelerations. In those cases, we tried to string things out ahead of time. I’m sure Mini-Shred will dig it. I will say that negotiating this bike in a group will be significantly easier than other tandems I’ve ridden. I think he’ll be totally jazzed.

  5. Fuzz

    An Ultegra derailleur with a GS cage, electronic or cable, will handle up to a 36T cog, as confirmed by Lennard Zinn, although you will likely have to put the B-screw in upside down. I put an 11/40 on my new bike, using a K-Edge conversion kit on an Ultegra Di2 derailleur. It’s working well. My next experiment is to swap the 50T big ring for a 46T ring. A 50/11 is wasted on me, as it is on most recreational riders. I love that you harp on the drivetrain folks to start with a 12T cog. The 46T may be problematic, as I will not be able to lower my derailleur sufficiently to achieve the desired 1-3mm gap to the big ring, but at about 5mm, I hope to be close enough.

    1. Author

      Yeah, once you go off-piste, there are some additional options out there. In this setting, which is to say, in working with Shimano, they weren’t willing to do anything that wasn’t in their spec sheets, which I respect. Glad to hear our musings on gearing resonate with you.

    2. Nik

      Hey Fuzz, I just put a 44T big ring (from WickWerks) on my Specialized Diverge that previously had a 50T. When the derailleur is in the lowest possible position, the gap is probably 4mm, but it still shifts 100% fine. I switched to a Shimano FD-CX70 front derailleur at the same time, I don’t know if that helped.
      So with a 46T I expect that your front derailleur is going to be just fine.

      I am enjoying the 44T chainring. It’s sufficient for going over 30mph, and it reduces the need for shifting the front derailleur.
      Now if only I could pair it with a 30T small chainring !

  6. miles archer

    That’s not a cheap toy. I paid less for my first new car.

    Having said that, taking your kid places on a bike is awesome.

    I await the article some years in the future when your son asks “Dad, can I borrow the tandem?”

    1. Author

      It’s more than my first two cars, together.

      That will be an interesting and, hopefully, delightful conversation. I look forward to it.

  7. winky

    Another advantage of the Gates belt is that when you break this thing down for transport it’s non-greasy. Just pop it off and throw it in the box.

    I’ve really enjoyed these two articles about the tandem.

  8. Joe

    Really interesting write-ups, I’ve been looking at the PeriScope for a while. Currently have an old Cannondale tandem that would fall into your ‘steers like a school bus’ category, that I’ve used with my older daughter and with my wife to a limited extent. Have you tried the PeriScope with the an adult Stoker – I’m curios with that long extension on the seat post how the bike handles for those excursions with grownups.

Leave a Reply

Your email address will not be published. Required fields are marked *