...those that are questioning the validity of disc brakes do not have disc brakes. Validity or necessity? They are two very different things. Disc brakes work, but so do rim brakes as do drum brakes. The biggest variable in any braking situation is rider judgement, experience and the amount of care that went into the selection, set-up and maintenance of a given bike or tandem's brake system.
Complexity? They are no more (or less) complex than a rim brake except that they don't use your rim as a rotor. Complexity is related to conversion, more so than anything else, particularly if you are considering dual discs. Discs require disc-compatible hubs as well as a frame and fork that will accept the disc. For manufacturers/consumers, there is the added cost of making a frame compatible with discs, disc-specific components and the added weight of those components assuming a tandem doesn't require a drum brake. Bear in mind, the installation of a rear disc still precludes the installation of a drum/drag brake... which can be yet another consideration for some teams under the heading of "complexity" if they are borderline drum brake candidates.
[discs have] certain advantages They also have certain disadvantages, in that 700c disc compatible wheels still aren't something that are readily available in the event of a disc wheel failure, front disc wheels in particular. They also use-up their brake pads at a much faster rate than rim brakes for folks who ride in challenging terrain where brake use is heavy. Therefore, brake pad adjustments and changes need to be made more frequently. Some captains may also get a false sense of security that causes them to push their tandem and its discs to a point where they simply create the risk of brake fade at higher speeds than they would have with only rim brakes if they're not mindful that even discs can be over-used.
A v-brake equipped bike would need a drag brake to keep from blowing up the tires on a descent like that Perhaps. Not all rim-brake equipped tandems blow-off tires and the likelihood that someone will over-use their rim or disc brakes to the point where brake fade makes them nearly useless can be the same. Again, the most important part of the "brake system" is the operator, to include selecting the correct brakes for how they will use their tandem as well as how to use and maintain those brakes. For some of the most challenging, long descents a drag brake may still be the best choice for many riders as they have the added benefit of reducing the hand-fatigue that can come from constantly applying brakes for extended periods of time.
One thing I noticed about "L's" disc was that the rear caliper was mounted inside the rear triangle on the chainstay. Ours is mounted outside on the rear dropout. True. A tandem or bicycle can certainly have the rear triangle designed around a disc brake installation. Our '98 and '02 Erickson tandems had their mechanical discs mounted between the stays with an attachment point on each to distributed the loads. daVinci has used a similar placement for many years, as has Santana vis-a-vis their very nifty chainstay-mounted brake adapter that supports either a pac-man for a drum or a caliper for discs. Co-Motion finally switched to the between the stay position a couple years back after mounting theirs up and behind the rear drop-outs. While I prefer the between stay installation, I can also appreciate why builders like Calfee stick with the other approach. Both work just fine.
It seems to me that a front-line tandem builder could change the dropout or dropouts to disc brake compatible ones without scrapping the entire rear triangle. It all depends on how the frame's rear triangle was originally designed and fabricated. As an OEM, Co-Motion will rework their frames to an OEM standard: very prudent. However, a custom frame shop might opt to go about it a different way, i.e., swapping out the original left stay for one that is beefier with an I.S. mount and appropriate clearances for the desired rotor size. Again, this is a decision a tandem owner must make when considering changes to accommodate different braking systems.
Discs are awesome and are clearly the future. Discs do work well, but they are merely an option: not the future. V-brakes were also heralded as the "future" for tandems, yet many enthusiasts still find that either standard cantilever or caliper brakes are more than adequate for their needs and expectations.
They aren't worth taking a loss on your present ride (unless they are) but if you actually have the choice! Definitely go with the mechanical disc. No, only consider discs as another option and factor them into your decision process. Talk with a qualified dealer or builder and be honest about your needs and expectations. Some teams may find that they'll be better served by discs, whereas others may still need rim + drum/drag, and others may only need rim brakes, but would benefit from having the ability to fit a rear-only disc or perhaps a drum "just in case" they need or want added flexibility in the future.
Hydraulic discs are an entirely different beast and if someone used the word "complexity" when talking about hydraulics I wouldn't really be able to disagree. I've used hydraulics on our off-road tandems since the late 90's. They're only complex if you don't have any experience with hydraulic brake systems. The issue with hydraulics is their suitability for road use vs. off-road. Again, you'll find a few teams that have used them on road tandems with great success... one team in particular who circumnavigated the globe and put them through some very demanding descents.
Frankly, having ridden tandems with just about every type of brake system in a variety of different road and off-road conditions for many years... I'm just thrilled that we have a number of options, of which discs play a part.
Bottom Line: It's all about having options and understanding which one is best for you.... or finding someone with the knowledge and experience who can help you figure out what might be best if you're unsure.
Last edited by TandemGeek; 05-30-12 at 10:24 AM.