Jan Heine wrote a similar article about disk brakes. You can find it via The Google or on Jan's blog.
I'd be very cautious about putting a disk brake on a tandem. As Jan points out in his article, putting the braking forces at the end of the fork blades requires that the fork be much stronger than normal in order to resist the flexing created by the bike and rider's momentum fighting the brake. Standard rim brakes keep those forces at the top of the blades near the fork crown, which is much stronger (that's also why builders like Alex Singer put their centerpull brazeons very close to the fork crown--it makes the brakes stronger and more effective). The tandem I used to own had a drum brake on the rear whose sole purpose was to keep downhill speed in check. I controlled it via Suntour barcon--put the brake on partially at the top of a long hill and leave it there to keep from going too fast. Actual braking was done by brazed-on cantilevers. --Eric N www.CampyOnly.com CampyOnlyGuy.blogspot.com Twitter: @CampyOnlyGuy > On Apr 20, 2017, at 3:42 PM, René Sterental <[email protected]> wrote: > > As I'm gearing up to enter the wonderful (hopefully for my wife) world of > tandem riding, and am getting set to build up my upcoming Hubbuhubbuh > sometime in the next month after the frame is delivered and in between my > business trips, I'm starting to do some research to better understand how > tandems work and behave. > > I was debating the merits of having the captain (me) control both front and > rear V Paul B-brakes and having my stoker control the disc brake, which is > supposed to be a drag brake (learning what that means), vs. me controlling > the rear disc brake and the stoker the rear V brake when I discovered this > excellent article on the Santana website (which is opposed to what most > people do with tandems). I really enjoyed the explanation, the data > supporting the claims and the enlightenment it gave me, that I decided to > share it here for the benefit of other (like me) total newbies to the world > of tandems. > > It all makes perfect Rivsense. > > UNDERSTANDING BRAKING > > Today, all of cycling is infatuated with disc brakes. A common belief is that > bicycles are finally catching up with the technology of cars and motorcycles, > where disc brakes proved superior decades earlier. If you accept this common > premise you might view rim brakes as old-fashioned, or destined for the scrap > heap. After all, you might be thinking, mountain bikes have already switched > to discs. Can road bikes be far behind? > > “Shouldn’t my new tandem come equipped with a shiny pair of disc brakes?” > > Actually, no… > > What’s missing is the simple realization that a bicycle’s rim brakes are, in > fact, disc brakes. Rim brakes have always been disc brakes. When cars and > motorcycles were fitted with disc brakes, they caught up to the braking > efficiency bicyclists had known for a half-century. > > But, you might ask, aren’t motorcycle-style disc brakes more powerful? > > Surprisingly, no. The engineers at Shimano and Avid (companies that produce > both types) have confirmed Santana’s test results. Even the newest and most > powerful bicycle disc brakes haven’t yet caught up the power of the best > V-style (or linear-pull) rim brake. > > The inescapable limitation for the motorcycle-styled brakes is that the rotor > (or disc) is too small. Anyone who understands bicycle disc brakes will agree > that with exactly the same hand lever, hand strength and caliper, an 8-inch > (203mm) disc will stop a bike about twice as effectively as a 4-inch disc. > This is true because braking power is a function of leverage, and is directly > proportional to the length of the lever arm (which, in the case of all > bicycle brakes, is the distance from the axle to the braking surface). With a > rotor twice as large, the same amount of hand power provides doubled braking > power, which allows you to stop twice as quickly—and in half the distance. > > More Leverage = Faster Stops > > A rim brake’s advantage is the diameter of the rim. On a 700c road bike the > diameter is 622mm. From this we can appreciate that a road bike’s rim brake > applies power at a leverage point that’s over three times more effective than > that of an 8-inch disc. While bicycle rim brakes may seem crude or old > fashioned, a 300% difference in leverage (and braking power) can’t be > ignored. Additionally, those who value overall efficiency should also > consider that a rim brake’s “disc” is not only three times larger, the weight > savings of using an aluminum rim as your rotor saves a half-pound per wheel. > > Single bike riders (along with the engineers at Shimano and Avid) will reply > that disc brakes have more than enough power for single bikes. We agree. On a > single bike, a rear 8-inch disc has enough power to lock the rear wheel. On a > tandem, however, an 8-inch disc isn’t powerful enough to skid the rear tire. > Think we’re wrong? Take any road tandem with a rear disc and (with a stoker > aboard) attempt a rear wheel skid on smooth, dry, level pavement (without > applying the front brake at the same time). People who try this test are > invariably disappointed when they fail to skid the tire. Next, perform the > same test on any tandem with a rear V-brake to prove to yourself that rim > brakes are considerably more powerful, and will easily skid a tandem’s rear > tire. > > Look at is this way: If a 6-inch rear disc is barely powerful enough for a > single, a twice-as-heavy tandem will need a 12-inch disc to obtain the same > degree of deceleration. If someone tells you an 8-inch disc is “powerful > enough” for a tandem, you should ask if a 4-inch rotor is a good enough for a > single. > > In an Emergency, It’s the Front Brake that Matters Most > > Because of “load transfer” the front brakes of cars, motorcycles and bicycles > provide over 80% of emergency stopping power. This explains why bicycle and > car manufactures typically supply bigger discs up front. While a larger-than > 8-inch rotor on the front of a single bike is questionable, that’s only > because a single bike’s stopping power is limited by the “over the bars” > factor. On tandems and cars, however, the limiting factor is front wheel > skid. In an emergency situation the load transfer causes rear tires to skid > with about 4x less braking power than a front brake. If disc brakes aren’t > powerful enough to skid the rear wheel of a tandem (and they aren’t), putting > this brake on the front of a road tandem (where four times more braking power > is needed) is worse than stylishly silly; it’s undeniably dangerous. > > Is dangerous too strong a word? Consider the following real-world scenario: > You’re cruising through town on your road tandem when a non-observant > motorist turns left across your path. Lacking the time to drop your hands to > the more powerful braking position, you’ll instead apply as much braking as > possible from the tops of your brake hoods. If your reaction time is slow > and/or your brakes aren’t powerful enough, the car will run into you. In > collisions between a bicycle and a car’s front bumper, the weight and speed > of the car determines the force of the impact. Death is not uncommon. If your > braking and/or reaction time is a bit better, you’ll run into the side of the > car instead of having the car run into you. Because the energy of the impact > is likely to be reduced by a factor of five, your injuries will be less > severe. But if your reaction time or tandem’s front brake is a bit better > still, you’ll slow up just enough to miss the car’s rear bumper by an inch. > In this case you’ll only have a laundry problem. Is the power of your > tandem’s front brake important? Ask your stoker. > > In summary, a front disc brake on a road tandem is as silly as a road single > without a front brake. In either case emergency braking is inadequate. Unless > bike discs become 3x more powerful (which won’t happen) the best answer for > the front of a road tandem will continue to be a long-armed (higher leverage) > V-brake. > > Page last updated > Wednesday, November 2, 2017 > © 2017 Santana Cycles, Inc. > > > > > > > > -- > You received this message because you are subscribed to the Google Groups > "RBW Owners Bunch" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > Visit this group at https://groups.google.com/group/rbw-owners-bunch. > For more options, visit https://groups.google.com/d/optout. -- You received this message because you are subscribed to the Google Groups "RBW Owners Bunch" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. 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