Moving in Stereo, Part I

Moving in Stereo, Part I

I like tandeming. I wouldn’t ever want it to be the only kind of cycling I did, but without tandems the cycling world would be less interesting. Imagine a world in which there was no caramel. Yeah, like that.

I’ve been riding tandems since the late 1990s, mostly with girlfriends, but that evolved into riding with Mini-Shred once he got big enough to ride a bike of his own. The child-stoker kit worked on my old Cannondale, but it was elaborate, heavy and mounting required him to make moves similar to climbing a tree.

All of this gave me an excuse to finally check out a tandem from Co-Motion. I’ve known CEO Dwan Shepard since the ’90s, when I reviewed one of their singles. It was a pretty stellar and versatile bike. More recently, I got to ride a Nor’Wester at the Oregon Gran Fondo. They have stayed on my radar not just because Shepard is such a nice guy, but because a number of friends have recommended them due to how well their tandems handle. It’s worth mentioning that Co-Motion was founded in 1988 and still has two of the three founders as owners. It’s as stable a company as we see in the bike industry.

And then they went and invented what might have been the single coolest tandem innovation ever, the PeriScope—a telescoping seat tube that allows the bike to accommodate everyone from Tyrion Lannister to Wilt Chamberlain. When I saw friends of mine taking their two kids on family trips with a pair of these tandems, well I started to fantasize.


The PeriScope Torpedo
It’s a great name for a tandem, no? Among the many models Co-Motion offers, in broad strokes the PeriScope Torpedo is a drop-bar tandem made from chromoly and featuring the aforementioned telescoping seat tube. Instead of a traditional design with both a top tube and a direct lateral tube (the tube in the middle that usually runs from the head tube to the stoker’s BB), the Torpedo employs a single, radically sloping top tube. They can get away with this due to the large diameter steel tubes with which they build.

Traditionally, one of the strikes against most tandems is that either they weren’t stiff enough to handle in a reliably predictable way, or they were stiff enough but because they used straight-gauge tubing they rode like the tires were pumped up to 200 psi. All of the chromoly tubing used in the Torpedo is butted, which makes the tandem lighter, stronger and more comfortable.

Traditionally, high-end tubing is double-butted. That is, each tube has two butts—thicker sections—one at each end of the tube. Co-Motion uses proprietary tubing of their own design. They own the mandrels and source from suppliers they have concluded have the best ability to meet their technical specs. The tubes features zonal butts; in addition to the butts at each end of the tube, in the case of the top tube, there is yet another butt in the middle of the tube, where it is joined with the captain’s seat tube.

The tubing diameters are enormous, compared to tubes on any steel single you’ll run across. Tube diameters go like so: top tube 44.5mm, down tube 48mm, seat tubes 38.1mm and the boom tube is a whopping 60x40mm oval. The seatstays are 16mm and feature an S bend, while the chainstays taper from an oval 36x22mm to a round 22mm at the dropout. The head tube is 44mm while the steerer tapers from 28.6mm to the HS race. The fork blades begin as a 35x28mm oval at the unicrown and taper to 19mm at the dropouts.


Two details Co-Motion doesn’t release are exact alloy spec or wall thickness. The former could reveal their source, while the latter gets into details armchair experts may second guess. They’ve tried many options and settled on what they, certified tandem experts, liked best.

Co-Motion deserves some recognition for taking significant steps beyond just building frames. They manufacture a number of frame components in-house, such as the dropouts, steerer tubes, bottom brackets, head tubes, bottom bracket shells, self-locking BB eccentric, BB cable guides, seat collars and the PeriScope seatmast system. The PeriScope is notable also because the clamp’s design eliminates the need for a slot in the seat tube, not to mention the traditional seat clamp, both of which which frequently end up being failure points for many frames.

By taking control of so many details they are better able to control not just quality of production, but exercise much more control over ride quality and ultimately the rider experience.

While the Torpedo is a stock bike, Co-Motion has the ability to customize any bike for an upcharge. And their ability to customize is nearly limitless. Rack mounts, pump pegs, S&S travel couplers, all of that is easy stuff for them. For this bike, I went with a steel fork rather than carbon so that we could do mounts for both fenders and racks; we did rack mounts in the rear as well. We decided to add S&S couplers; they make traveling with the tandem a good deal easier. With a couple of packing blankets, I can break the tandem in two and put it in the back of my car in order to drive to the start of a ride, not to mention flying someplace for a vacation.


Before I go into the build of this bike, I want to point out that the standard base model of the Periscope Torpedo comes with Shimano 105 and TRP Spyre mechanical disc brakes (and a 200mm rotor). It goes for an ultra-reasonable $3895. There are at least a dozen ways you can customize your bike, from custom sizing to S&S couplers to racks and panniers. Don’t let the initial spec list fool you.

Shimano’s decision to discontinue road triples and SRAM’s outright hostility to multiple chainrings meant that we had to give some thought to the build. I’ve experienced how poorly tandems can shift thanks to a six-foot-long derailleur cable. Mini-Shred puts out about as much wattage as a night light so we didn’t need to worry about a 56-tooth chainring. I opted to go with the da Vinci compact crank as their stoker crank comes with three drillings for the pedals, meaning the cranks effectively accommodate 130, 150 and 170mm crank lengths in a single unit. Perfect for growing people.

We opted to build the rest of the tandem with Shimano’s Ultegra Di2 disc group to give me flawless shifting and the power of hydraulic disc brakes. Co-Motion uses a proprietary seatpost, owing to the diameter of the seat tubes. To Co-Motion’s telescoping stoker stem, we mounted a cowhorn bar, turned backward, to shorten the reach Mini-Shred would have to make to the bar.

Some cyclists love to argue about innovation vs. necessity. Disc brakes aren’t necessary and electronic shifting is just another breakable doo-dad being rammed down our throats. It gets tiresome whether it’s happening here in our comments or when I meet people on the road.

Of the many selections made for this tandem, none have paid off more than the choice to go with Ultegra Di2/hydraulic. Not only is this group practically flawless in operation, the futz-free shifting and powerful braking make this the most easily controlled tandem I’ve ridden. The improvement in shifting and braking is so stark as to make the ride more relaxing.

In addition to being the home to Co-Motion, Eugene, Ore., is the home to Rolf Prima wheels. They’ve been making wheels for tandems for ages and may be the only company making a tandem-specific wheelset. They came highly recommended; I’ll be reviewing those in a separate post.

For Part II, click here.

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  1. Brian Lockhart

    Nice rig!!! Now you’ve got me thinking of getting a tandem…

    And re: DI2 + hydraulic discs – yeah, if ever there was a *perfect* place to apply these two technologies, it’s on a tandem. Just for the sheer benefit of getting away from the “sloppiness” that happens when you have brake and shifter cables + housing that are THAT much longer than a normal bike. No more sloppy shifting or weak brake lever feel.

  2. Willis

    Very nice rig! We used the Burley child stoker kit on our old Santana Arriva with my girls as they we growing up and it was a blast. They ALWAYS loved to give me the speed readout from the stoker computer and compare who went faster. I agree with you though that the PeriScope is a much better solution for kids as stokers.

    My wife and I have been tandem riding for 21 years and 2 tandems. We currently ride a Santana that has the Shimano Sweet 16 wheels mentioned above…we have about 2,500 miles, (not my only bike either), on them with the only issue being in the initial 100 miles. I had to have them re-tensioned by our local wheel guru and they have been fine since. Looking forward to your review on the Rolf wheels.

    On the points about shifting and braking. I would have gone electronic/hydro too if those had been available when we purchased our current rig. The only way to get mech shifting to work correctly with cable runs that long is to use Ride On cables. I think Gore has ceased mfg. those so not sure what a current alternative for mech shifting would be. Definitely go electronic if you can afford it. Discs will always be preferred over rim brakes with a typical tandem load. Same precautions though…one needs to be mindful not to overheat the brakes…rim or disc.

  3. Ronnie Bryant

    How do you handle the rear brake when the Tandem is un-coupled and packed? SInce it is hydraulic, how do you handle the hoses?

    1. Author

      So the hose is attached via zip ties. I’ll be able to remove the rear caliper, cut the zip ties and then pack it up. It does mean that I need cutters and more zip ties in the case, though. Mind you, all this is theoretical, I haven’t actually traveled with the bike yet; I wanted to get the review up now, as my previous S&S experience leads me to think I won’t have trouble with this.

    2. Grego


      Small releasable cable ties like these might work for your ziptie needs on the tandem: Panduit PRT1.5S-C0, HellermanTyton RT40R0C2.

    3. Andrew

      I’ve used releasable ties for event route signs for a number of years now.
      A couple of tips,
      – To help release the tie pull a little extra tension on the tail to take the load off the catch pawls.
      – Still carry spare ties as the catch mechanism does suffer degradation over several tensioning/releasing cycles and eventually fails to hold. (Note: we’re pulling the ties very tight to guard against wind blowing signs around so you might get longer life out of them.)

      An alternative if you were using standard ties would be to place the catch housing away from the hydraulic hose/line and to remove the tie cut through the catch above the wrap of the tie’s band.

      An alternative alternative would be to use velcro-style cable ties in appropriate locations.

  4. GT


    Heard you talking about the paint colour in the podcast the other day and I was intrigued, oit certainly looks the goods.

    Is it possible to get an amendment to the article? Well, more a visual amendment, i.e. a pic of you and Mini-Shred on the tandem?

    1. Author

      Haven’t managed to get a usable one so far, but trust me, I’ve been working on it and once I have one, I’ll find an excuse to post it.

  5. winky

    The huge flexibility in the rear cockpit size is such an obvious advantage (in hindsight) one wonders why they aren’t all like this. Electronic shifting for the rear derailleur is also obvious. Great bike.

    If I was riding a tandem with a full-size partner in the mountains, I’d give the stoker a full set of V-brakes as well. You’d never sweat the stopability.

    For packing, I imagine the frame being Z-folded with no hose/cable disconnection required. But I am likely very wrong.

    1. Author

      It’s vaguely possible that you could get the full frame in one case and just pack the wheels, seatposts/seats and stoker’s bar in the other case. Haven’t had the opportunity to really explore that yet.

    2. Andrew

      I’m sure I recall descriptions of touring tandems with rim brakes also having a drum/drag brake in the rear wheel operated by a friction lever from the stoker’s position. Especially for use on long descents.

      So dual braking systems are certainly a known tandem feature. However rim brakes have improved a lot, and disk brakes have eliminated rim-overheating problems. So whether you’d actually need additional brake/s either for overall braking capacity, or for redundancy, would really depend on typical loads, typical terrain ridden, and riders’ preferences.

    3. Author

      I don’t really want to get into a big debate on brake systems and braking configurations here, but I am going to take a moment to say that I’m not a fan of turning a set of brakes over to the stoker. I make a small exception for dialing in a drag brake, per captain’s request. The fact is, any time you hit the brakes, it stands the bike up and to have the stoker suddenly decide to clamp down on a pair of V-brakes could end poorly by throwing the bike’s balance off. Consider if the passenger in your car had a brake pedal and could suddenly apply it any time they felt like it. That could be mayhem. Disc systems are so good now that I don’t think a secondary brake system is necessary, unless, perhaps, you ride in a place with exceptionally steep mountains or both captain and stoker are, shall we say, plus-sized.

  6. David Hunter

    Great setup on your tandem. We have been riding the triple version of this bike for 5 years now and it has been an amazing machine. The flexibility of the fit for the stoker is awesome for families and even lets us ride with other adults as stokers and then with our bike we can even convert it from a two seater to a 3 seater in just a few minutes. I just wish we had a way to run DI2/hydraulics and still make the conversion.

  7. Velociraptor

    Shimano still has road triples in the form of Tiagra 4703 and lower. Ultegra (6703) and 105 (5703) components are still readily available. Note that the 105 triple crankset (74mm BCD, 5 bolt) is your best path if you want to run a 24t inner chainring.

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