Understanding Braking

Santana Brake Options

Generation 4 Disc Brake

Two things lead Santana to create the industry's only 10" disc rotor and the only rotor and caliper specifically designed for tandems:
1. The demise of the drum brake left riders who like a drag brake looking for a modern solution. No rim brake or existing disc brake could handle sustained dragging down a mountain.
2. With the V-brake as the benchmark for power, using existing 7" or 8" rotors on a 700c wheel resulted in LESS brake torque for a given lever effort.

We found a brake caliper that used metal rather than plastic bushings and high grade springs to withstand extreme heat, then modified it with a quicker action and stronger return spring to handle the extra cable length of a tandem. We developed a 10" disc rotor to increase brake torque, absorb more heat, and shed heat faster. 3 generations of rotors saw slightly changing spoke and hole designs to reduce warping, run quieter, and resist lateral flex. Our new 4th Generation rotor represents a giant leap forward in these criteria and drops 90 grams! Two piece button construction with aluminum spider and cooling fins and new cutout patern means quieter operation, no rattle over rough roads, more consistent feel on long descents, and longer pad life. Available only on the rear and recommended for riders who do sustained, steep descents or like to drag their rear brake to control speed on moderate descents. Also for riders who want to run up to a 42mm tire or fender.

Shimano Road Caliper

Available in Dura-ace or Ultegra levels for front and rear the classic road bike brake caliper is the lightest, simplest solution and the newest generation boasts tandem capable power nearly on par with a V-brake. Boasting easy setup with generous pad-to-rim clearance caliper brakes require the least amount of attention to keep them centered and working their best. Santana paid careful attention to the design of our frames and fork so that you can mount up to a 32mm Continental Gatorskin tire with road caliper brakes which is the biggest most people will want for pavement use. This brake is recommended in the front for riders who prize low weight, less adjusting, and traditional looks over the slight extra power and greater tire clearance of a V-brake. In the rear we recommend a road caliper for riders who's terrain or braking technique don't demand the heat capacity of a disc and don't plan to mount a fender or dirt tire. How much lighter is a twin road caliper setup vs a front V-brake and rear disc? About a pound and a half.

V-brake

Available on the front of all our bikes and on the rear of the Arriva, Nuovo Sport, Spirit, and Sovereign models the linear pull or V-brake creates a tremendous amount of braking torque relative to lever effort and has plenty of clearance for fenders or the largest tires you can fit through the frame or fork (usually 42mm with knobs). Riders choose this front brake when they need all the clamping force they can get or plan to venture onto gravel roads and want to mount up suitable tires and they don't mind an occasional centering adjustment to keep them working their best. In the rear a V-brake is a more economical alternative to a disc when you need more tire clearance and braking power than a road caliper offers but you don't need the massive heat capacity of a disc for dragging down long descents.

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.

BRAKE TECHNOLOGY
SEE ALSO

Understanding Braking
Power vs. Heat
Disc Brake Technology
•••Mechanical vs. Hydraulic
Avid Brakes
Hierarchy of Braking Power