Braking for Tandems - from the Santana website

[René Sterental]

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.

 

 

 

[Patrick Moore]

I understand the theory, but I wonder if it corresponds to reality? The standard sized (140 mm?) rotor on the front of my Matthews provides as much braking power (ie, ease of locking front wheel) as any V brake I've used. Granted, single, but I've ridden tandems with shorty Vs and cantis and I can't extrapolate any deficiency to come up with a disc brake deficiency here -- and I'm talking about mechanical discs, not hydraulics, in regard to which the assertion is surely wrong.

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[Bill Lindsay]

That truly is a forward-thinking article....considering it was written in the future!  It was written in November of 2017!  Do they have flying cars in the future?  

Bill "Marty-McFly" Lindsay

El Cerrito, CA

[Eric Norris]

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

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[René Sterental]

Bill, good catch on their typo! Ja ja ja ja!!!

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[René Sterental]

The Hubbuhubbuh comes configured with only a rear disc brake, just like Santana recommends. When I spoke with Grant last year, he explained the concept of the drag brake, and in their demo tandem, it was the stoker who controlled it. I can't remember if the lever was different to be able to keep it partially depressed to keep the drag constant, or if the stoker needed to keep pressing it to slow the bike. I'll check when I go there, but am interested in the reference you make to how Eric controlled it with the Suntour barcon. 

Eric, can you explain it to me?

Thank you,

René 

[René Sterental]

Oh, I see. I did a search on Suntour Barcon and realized you are controlling the drag brake with a friction shifter. Ingenious!

I wonder if it makes more sense to have the captain control all the braking, which means that adjusting the drag brake while already on the descent means releasing the rear V-brake, or have it as Grant configured it, where the stoker regulates the drag brake.

Just as long as the stoker doesn't want to just force the captain to just go slower... :-)

René 

[ted]

If the stoker thinks it's too fast, better slow down.
First rule of tandems: the stoker is never wrong.
Second rule: see first rule.
Third rule: ibid

[René Sterental]

Ja ja ja ja!!! Very true. 

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[Ray Varella]

I've had a tandem for over 30 years and my drag brake is an Arai drum.
It has been controlled by a Suntour bar on until recently and it is now controlled by a Suntour thumbshifter.

In many years of tandeming, with numerous different stokers, it is my humble opinion that it is asking a lot of a stoker to be attentive 100% of the time so they can apply the drag/emergency brake.
For a dedicated tandem team that always rides together and the stoker is always attentive, things may be different.
My personal experience is to communicate bumps and intentions to the stoker but to handle all the controls for the sake of safety.

I wonder if a barcon pulls enough cable for a disc?

Ray
Vallejo CA

[René Sterental]

Great insight! Thank you for sharing it.

One question on the barcon for the drag brake. What kind of cable do you use? Shifter cable that fits in the barcon but may be too thin, or brake cable that is thicker and may not fit through the barcon? Or were these Suntour barcons capable of handling both?

René 

[Ray Varella]

Rene,
I've always used shifter cables in mine. I've never given it a second thought but I routinely inspect brake cables, doubly so on my tandem.

Drag brakes also make excellent perking brakes which makes parking a tandem a bit easier.

Ray

[Tony McG]

I agree with Ray. I replaced the vintage STI/Erickson Gizmo and XT v-brakes/travel agents on my 20y/o Santana with Gevenalle Audax shifters and Paul MiniMotos. The drum brake was controlled by the captain with a Shimano friction bar end shifter. I have disc brakes on my Fargo, Pugsley, and Powderkeg, and I don't think they stop any better than the MiniMotos.

[René Sterental]

Thank you both for the feedback. 

Do you think the braking power of the MiniMotos is the same as the Motolites? I know the Minis are for canti levers and the Motolites are for long pull levers, but I'm talking about pure braking power. Are they the same or is the longer Motolites with the longer cable pull more powerful?

René 

On Fri, Apr 21, 2017 at 10:04 AM 'Tony McG' via RBW Owners Bunch <rbw-owne...@googlegroups.com> wrote:

I agree with Ray. I replaced the vintage STI/Erickson Gizmo and XT v-brakes/travel agents on my 20y/o Santana with Gevenalle Audax shifters and Paul MiniMotos. The drum brake was controlled by the captain with a Shimano friction bar end shifter. I have disc brakes on my Fargo, Pugsley, and Powderkeg, and I don't think they stop any better than the MiniMotos.

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[Tony McG]

I have no experience with the Motolites. I needed a v-brake that would work with drop bar brake levers. If I didn't have a stoker on the back, I think I could have stood the Santana on the front wheel; those brakes saved our lives more than once...

[René Sterental]

Thanks! Good to know that the MiniMotos work so well.

[Michael Hechmer]

This topic has been raging on the Tandem@hobbes list for the entire winter.  It's been physicist vs physicist and I am not about to jump into the argument.  A lot depends on the kind of riding you do.  One thing I will offer for those new to the tandem world.  Because of the added rear weight in a tandem the rear tire has better adherence and therefore provides more braking power than the rear brake of a half bike.

Michael

[Steve Palincsar]

Well, for sure you aren't going to lift the back wheel off the ground!

[René Sterental]

Right. The Santana article pointed that out and their argument was that whereas the hard braking risk on a regular bike is for the rider to go over the bars, on a tandem is for the front wheel to slide under if locked, which has catastrophic results. 

I'm going to look for that tandem group. Do you have an address?

René 

[Julian Westerhout]

Rene, 

From the tandem list: 

-- tandem@hobbes: The Internet Mailing List for Tandem Bicycle Enthusiasts --
Post to: tan...@hobbes.ucsd.edu  (include your real name )
How to subscribe: http://hobbes.ucsd.edu/tandem/info.html
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Julian Westerhout

Bloomington, Il 

[René Sterental]

Thank you!