Hi David, 

We are new members too - we bought our first tandem - a Circe Helios - in March - it fortuitously arrived just in time for lockdown and we've done 1100km since. The set up works perfectly for me as a rather short pilot and my 10 year old daughter as stoker. 

Hopefully someone might have some words of wisdom on the Eos..

Sarah

By way of update.....I decided to purchase the Circe Eos that was up for sale on facebook recently, our first foray into tandem world without too much fuss in decision making. The fact the Circe tandem was designed to accommodate a range of sizes by personnel associated with making the versatile Airnimal folding bike gave me the confidence to follow my gut instinct that this tandem would work for us.

After a couple of weekend and evening rides over the steep Bronte hills around Hebden Bridge we love the practicality, adjustability and ease of transport and storage especially the fact these features don't detract from the feel of a quality ride. With wheels,rack and mudguards  removed the bike sits readily into our ford focus estate for transporting if we need to drive to a prefered starting point.

The 26” wheels on 28 continetal  gatorskins run nice and free. Dropped a hill friendly 11-32 teeth large ring cassette on to help with the steep hills with novice stoker. Found the 160mm rotors got really hot but we had just navigated a steep prolonged descent into Hebden Bridge on the back roads which included a very near miss with a black cat . As a result I’m just considering the potential benefit and feasibility of increasing the size of the rotors ( any observations from experience gratefully recieved)

All in all after just a few rides I’d certainly recommend the Circe EOS from what I’ve experienced so far.

The tandem, speedily relieved of its wheels, rack mudguards, seats,seat posts, bars and stem sits discreetly suspended from a couple of hooks in my attic office / man cave awaiting simple re-assembly for a weekend ride to the chippy / pub with the Mrs.......

 

Disc brakes  - my understanding is that disc brakes should be applied as and when needed rather than being used continually.

To slow the bike on long descents a rim brake can be used but hub mounted retarders like the Aral used on older tandems prevent rims overheating in these conditions.

Being brought up in Halifax I know just how steep the hills round Hebden Bridge are, and how narrow some of the roads are.

Happy riding, Boris permitting

The 160mm discs on our first tandem got really hot even using the on-off approach suggested above so I upgraded to 205mm discs, have them on the current tandem and haven't had a problem since, even with luggage.  If your Eos has BB7s then it should be a straightforward change (discs + adaptors).

Neil

Many thanks for your input

That's the natural option I was going to try..... I'd observed a seasoned tandem rider with large rotors on their relatively new Orbit Velocity.  I expect a degree of heat on the hills around hebden Bridge but I want to give the best change for heat dissipation.....

Thanks again..

David

 

Yes I'd definitely recommend 205mm rotors

160s are standard now on solos, so really not enough for a tandem.

 

Thanks Matthew 

Of interest....... What's your preferred maker of rotors for use with avid bb7's......

Thanks for your input

David

I have used Shimano, avid & tektro/trp rotors. Not had any problems,  but generally I avoid braking if I can lol. 

TRP produce some 2.3mm thick rotors - https://trpcycling.com/product/trp-41-standard-rotor/ -which they recommend for downhill mtbs /E bikes & also for tandems. Standard rotors are 1.6-1.8mm new. They should still fit into standard calipers,  but shoes may need adjusting. If you do a lot of braking in hilly areas these would be better at heat dissipation, last longer, warp less, for a small weight penalty. TRP41 = 1 piece,  TRP42 = 2 piece. 

I have one to try for a refurb project waiting in the wings 😳....

Many years ago there was a lot of discussion of disc brakes for tandems and I saved this report. I can't vouch for its accuracy, I think it is from about 2003.

SuDiBe Tandemseiten

Literatur

Disc Brakes

by Bill McCready

(Scheibenbremsen für Tandems - sehr viel Hintergrundinfos und ein wenig Werbung. Aufbereitet aus der

englischsprachigen Mailingliste, 11/2003)

This LONG post contains the following revelations. If you read it all, you'll discover the following and a

lot more.

Real disc-brake test results from Santana and Cannondale.

Avid has NOT certified their disc for tandem use.

Cannondale will adopt a new tandem disc brake standard.

In the meantime, Cannondale has shelved the Avid specification.

8 reasons to re-think dual discs

Santana has tested brakes for years. Our protocol has been published (on T@H) and distributed to

various disc brake manufacturers (including Hope, Formula, Shimano, Avid, Magura and Hayes).

Our short, steep test hill (Mountain Ave. in Claremont, CA) is a wide, smooth roadway. From the dead

end at the top to the bridge at the base is a distance of .67 miles (1,074 meters). The drop in elevation is

528 feet (161 meters). While the steepest portions exceed 20%, the entire grade averages 15%. Our "test

course" is open to everyone (schoolkids ride it daily). Besides the hill itself we use 400 pounds of riders,

a test brake mounted to the rear wheel (which can be rim, disc or drum), a front standby brake, plus

calibrated "blister" tapes and a digital infrared "gun" to measure heat. We use the test brake to coast

down the grade at 15 miles per hour. At two intermediate locations, a full application of the test brake is

used to bring the tandem to a full stop. The test brake is immediately released and, after a 5-second

pause, the bike is allowed to coast back up to 15mph. The test brake is then applied to maintain this

speed. If the brake is still functioning at the bottom of the hill, it is fully applied for a third time. As soon

as the bike stops, we take heat measurements. We've now tested nearly two dozen disc brakes. We have

always invited manufacturers to observe our tests (and Hope once sent a representative). If any of you

would like to attend a future session, send us an e-mail.

Because this is a pass/fail test of a brake's heat capacity, stopping distances are not recorded. The entire

test is completed within ten minutes. In order to pass, the brake must (1) maintain the 15mph test speed

between stops, (2) bring the bike to three complete stops, (3) not stick closed, and (4) not need new parts.

Sound easy?

The Arai drum brake passes, as does a tandem-specific version of the Formula hydraulic disc (with either

185mm or 203mm rotors). No other brake has yet passed. How do they fail? Cheap hub brakes (drum

and band) and some discs will fail before the first interim stop. Rim brakes and most disc brakes will fail

at or before the second stop. (Rim brakes don't actually fail, but the tire leaves the rim). Shortly after the

second stop the 8-inch mechanical discs from Avid and Hayes have lost all power (through fade), and can

no longer control downhill speed. After the standby brake is used to rein in the resulting runaways, we

note melted rubber seals (Hayes) and plastic adjustment pieces (Avid). In other words, these highly rated

"downhill" brakes with 8-inch rotors fail two ways: they can't control downhill speed AND they melt in

the process.

When I heard that Avid had revised their longstanding "not for tandem" rating, I contacted them and

spoke with Paul Kantor.

Q: Have you made any improvements?

A: No.

Q: Have you done any testing?

A: No.

Q; Why the change?

A: Cannondale and Todd Shusterman (Da Vinci Designs) have told us that our brake has passed their

tests.

Q: What were those tests?

A: We don't know.

PS: Before someone accuses me of a hatchet job, they should realize that Santana has, for many years,

installed Avid rim brakes on nearly every tandem we deliver. Because most tandem buyers (and bicycle

mechanics) are wary of hydraulics, Santana would love to offer a capable mechanical disc, and will work

with Avid (and others) to develop a non-hydraulic disc that is good enough for tandems.

Part 2: A History of Disc Brake Failures

Because tandem brakes have overheated with disastrous consequences, Santana has tested a brake's heat

capacity for over 20 years. During that time a number of manufacturers have produced unworthy brakes

that were eagerly purchased by tandem enthusiasts.

Most memorable to me was a decade-long disagreement that existed between Santana and Phil Wood

over the performance of his 1975-1984 mechanical disc brake. While the design of his lightweight brake

was inspired---and Phil actively promoted its use for tandems---we quickly discovered that the brake was

failure prone. Phil not only ignored our complaints, he flatly denied that a "real" problem existed. In the

winter of 1980, when John Schubert and Gary Fisher arrived in Southern California to test six tandems

for Bicycling Magazine, they wondered why Santana didn't use the Phil disc found on other brands. At

the time a Phil rear disc was not only the most popular option on custom tandems, Schwinn had removed

rim brakes to equip their Paramount tandems with dual Phils instead. The following day these two editors

(who didn't want to believe my story) failed a brand new Phil disc.

Was the failure reported? No. After Phil convinced someone at Bicycling that the failure was a fluke, that

particular test result was edited out.

Later, after at least three tandem teams experienced simultaneous dual disc failures, and Phil settled at

least two lawsuits (one, unfortunately, where a stoker was seriously and permanently disabled), he quit

selling the brake or any of its spare parts. Within a couple of years a thousand (?) of these expensive

brakes were retired when the owners could no longer buy replacement pads. In today's era of CPSCmandated

recalls, Phil Wood would have needed to spend a quarter million dollars to buy-back these

brakes. (And Schwinn would have needed to retrofit two-years of Paramount tandems.)

Is the Phil incident unique?

No. Over the years Santana has rejected nearly two dozen disc brakes. A more recent example was the

1990-96 Hope mechanical discs. While these brakes were merely ineffective, custom tandem builders

installed hundreds without question. Today, in spite of gushing reviews and glowing testimonials from

Hope's early customers, almost all of these Hope mechanical discs have quietly been removed.

Which brings me back to Avid.

Last summer, when Avid reportedly removed their prohibition on installing their discs on a tandem, I

called them and was surprised to learn that their change of heart was not based on product improvement

or internal testing. Instead, their new direction was the result of reports they had received from

Cannondale and Da Vinci.

P.S. By now you realize that this post is too long for a quick read. Instead of skimming this multi-part

post, why not print it (using recycled paper!) or save an electronic copy.

PPS: If, on the other hand, "A post from Bill..." causes boredom or anger, use the delete key!

Part 3: In search of valid test

When I asked Avid's Paul Kantor why Avid was no longer warning customers that their disc was

unsuited for tandems, he replied that test reports from Todd Shusterman (Da Vinci Designs) and

Cannondale had caused Avid to abandon their long-standing position.

When I phoned Todd Shusterman in September to talk about disc brakes, he was surprised to learn that

Avid had credited him with a test. Actually, he had reported to Avid that when and his wife had

descended France's Mount Ventoux using a rear Avid disc and front rim brake. His report to me included

the following:

While descending Ventoux's west road Todd had "let the bike run" on straightaways. He stopped part

way when he needed to readjust the pads on his rear disc. Upon reaching the town at the base of Ventoux,

he found he'd used his front brake enough to get his rim "too hot to hold." He didn't have a touring pack,

and says his team weighed 320 pounds.

My comments: Ventoux's west road is not as steep or twisty as the classic southern approach used in the

Tour de France. Although the steepest sections of this newer and wider road exceed 9% (according to

Michelin), the average gradient is a less remarkable 7.5%. The long straightaways on this route allowed

Todd's brakes to cool between turns. A mid-way stop (to adjust the disc pads) allowed additional cooling.

His use of the front rim brake further protected his disc. While the Shustermans should be admired for

their day's ride (a tandem ascent of Ventoux from any angle is an impressive feat) their westward twobrake

descent at moderate speeds was not a severe test of a tandem's disc brake.

While Todd was pleased with the performance of his disc, he did not imagine Avid would interpret his

report as a "real test."

At Cannondale I reached Mark La Plante, a 20-year veteran who runs their testing facility. The two of us

have now shared four long phone conversations about disc brakes and tandems. A couple of years ago

Cannondale devised a tandem-specific lab test for a disc brake that would simulate a descent of New

Hampshire's Mount Washington. Their calculated "braking torque" to descend the 7.6 mile, 12% grade at

a safe constant speed was 60 foot pounds. While Cannondale hasn't used this test for rim or drum brakes,

they've tested a number of discs. Amazing (to me) was that Cannondale and Santana tests contained

surprisingly similar elements:

Both tests rely on one brake. Gross test weight: Santana 435#, Cannondale 400#. Test speed: Santana

15mph, Cannondale 15.5mph. Ambient test temp: 70 degrees F (plus or minus 10F). Cooling: Santana

outside air, Cannondale electric fan.

The biggest difference in the test: Mount Washington: 12% for 7.6 miles. Mountain Avenue: 15% for

2/3rds of a mile.

Q: How many discs have passed Cannondale's "Mt. Washington" standard?

A: Zero.

Q: What about the Avid?

A: Avid's disc failed seven minutes into the 30-minute test.

PS: A T@Her who attended Interbike and stopped by the Avid booth, reported that he had talked to an

"Engineer." While Avid has a capable design staff headed by their President, Wayne Lumpkin, they've

never had an engineer, test facility or testing program. Their ball-bearing disc is produced by Wellgo, a

respected Taiwanese company famous for its pedals. Few Taiwan component makers have test facilities

either, as a nationally subsidized test center is a function of the Taiwan Trade Commission. While the

Trade Commission's test center is quite good, as far as I know they have not as yet developed specific test

criteria for disc brake performance. Santana and Avid have discussed some potential remedies for the

failure points we have found, and our companies will work together this winter to increase the heat

capacity of Avid's current design (which is limited due to teensy brake pad dimensions and inadequate

brake pad airflow---factors that are 3-4 times less critical on a design that was, after all, intended solely

for single bikes).

PPS: Following years of frustration with Asian suppliers, Avid turned to Italy and entrusted their

HYDRAULIC disc brake program to Formula, an experienced producer of motorcycle disc brakes.

Formula has engineers, test facilities, a race-support program and lots of hard-earned knowledge.

Because of Formula's development input and manufacturing expertise, Avid's just-introduced "Juicy"

hydraulic looks very promising (for single bikes).

Part 4: Cannondale's disc brake testing

Two years ago Cannondale's Testing Engineer, Mark La Plante, designed a tandem specific lab test to

simulate a descent of New Hampshire's Mount Washington (home of an annual bicycle challenge). After

every disc Cannondale tested failed this test, they cut their tandem brake standard in half. Instead of

applying the lever to achieve 60 foot-pounds of braking force, with their new test the brake lever would

be squeezed half as hard in order to create 30 foot-pounds of braking force. Still 30 minutes long, they

call their new test "Half Mt. Washington." (To put the 30 and 60 foot-pound figures in perspective, a

strong squeeze of a brake lever can create more than 120 foot-pounds of braking force).

When I asked Mark La Plante why Cannondale had decided to make their test twice as easy, his reply

was that without this change Magura's "tandem-approved" Gustav-M could not pass. While the original

"Mt. Washington" test may have been a reasonable real world standard, Cannondale was reluctant to fail

a "certified" brake from a respected manufacturer. By cutting their test in half, the Gustav-M could pass.

Once the bar was lowered, Magura's Julie also passed. And if Cannondale relaxed their standard a bit

further by allowing the test to be paused for pad readjustment, Avid's largest 8" (203mm) disc could also

pass.

I then contacted Buck Mitchell from Magura USA to purchase a 3rd-generation Gustav-M, and to ask

about their "tandem approved" rating. When the answer arrived from Germany, I learned that Magura

tests brakes for both power and heat. To pass their tandem-specific heat test a brake needs to produce

1000 watts of stopping power for 15 continuous minutes without boiling fluid or suffering from

excessive fade. And, after cooling, it needs to repeat this performance without needing readjustment or

using up more than 30% of its pads.

Here is a quick summary of tandem-specific disc testing:

Santana: 15% grade for 2/3rds of a mile.

Cannondale: 30 foot-pounds of braking force for 30 minutes.

Magura: 1000 watts for two tests of 15 minutes each.

Hayes: Subscribes to Santana's test.

Hope and Shimano: No tandem-specific test standard.

Avid: No testing whatsoever.

PS: It is interesting to me that Cannondale's reason for cutting their original tandem test standard by 50%

was to let a respected Magura disc pass. But then, in order to also "pass" an Avid disc, Cannondale

watered down its 50% standard to allow a mid-test readjustment---a "fudge" that is not allowed by

Magura's test standards.

PPS: Watered-down testing reminds me of two years spent on a local school board. If you can't get

students to pass, the tests are too hard!

Part 5: Avid denies "tandem certified" and Cannondale works on a new tandem disc test.

After Avid reportedly changed their long-standing prohibition on installing their disc brakes on tandems,

I gave them a call. Instead of a design change or test data, however, Avid referred us to Da Vinci and

Cannondale for their test results. Instead of a test, Da Vinci's Todd Shusterman related a successful

tandem descent of Mount Ventoux (13 miles averaging 7.5%). Cannondale's initial test was a simulation

of Mount Washington (7.6 miles averaging 12%). When the Avid brake failed this test, Cannondale cut

the required braking force from 60 foot pounds to 30 foot pounds. When the Avid disc failed the "Half

Mount Washington" test, Cannondale amended the protocol a second time to allow a pause for

readjustment. Based on passing this third version of a tandem-specific test, Cannondale's Product

Managers were allowed publish a tandem specification that included Avid discs. In the meantime,

Cannondale's Testing Department was unaware of Avid's still-in-place ban on tandem disc installation.

Because Santana had not yet tested the newest 8-inch (203mm) version of Avid's "not for tandems"

brake, in September we scheduled a retest to see if Avid's biggest brake would survive Mountain Avenue

(2/3 of a mile averaging 15%). In case you've forgotten, three brakes have passed our six-year-old test: a

standard Arai drum and two tandem-specific discs from Formula (185mm and 203mm).

When tested, Avid's 8" disc failed after one-half mile. As is sometimes the case, this test was a double

failure---the brake could not maintain the 15mph-test speed (excessive fade) and was disabled in the

process (melted adjustment fittings).

Instead of moving the finish line (!), we decided to mate a second Avid caliper (the first one could no

longer be adjusted) with a prototype 10" rotor. Unfortunately, at the half-mile point the Avid again

experienced "runaway" fade. Then, before the tandem could be brought to a stop, our prototype 10-inch

rotor warped. (We later learned that our prototype, a "show-only dimensional sample," hadn't been heattreated).

Because the adjustment pieces again melted, this test was a rare triple failure---warped non-Avid

disc, excessive fade and melted pieces.

When I visited Avid's Interbike booth two weeks later, Paul Kantor was not surprised by the failures. He

then "reminded me" that Avid has never "certified" the brake for tandem use!

Surprised by his remark, I asked for clarification. Kantor replied that with tandem builders (such as Da

Vinci and Cannondale) ignoring Avid's ban and performing their own tests, Avid has decided to abandon

their former position, and will let builders, dealers and customers make their own decision. Avid's only

change, Kantor continued, was to take "no official position" on tandem use. Kantor then directed me their

current OEM product sheet and expo signage. While recommended uses for Avid's mechanical discs

include cyclo-cross, touring, and recumbents, the word TANDEM does not appear on their list of

certified applications.

What about using the disc as a drag brake? Avid's installation instructions, while silent about tandem use,

specify that the cable must be attached to a "brake lever." Kantor, not convinced that anyone should

install an Avid disc on their tandem, thinks it doubly inadvisable that someone would attach it to a shift

lever.

When I spoke with him last week, Cannondale's Mark La Plante was in the midst of developing a new

tandem-specific disc brake protocol. After reviewing the issues, La Plante believes that the 30 foot-pound

braking force that allowed the Avid brake to pass is too low. He has decided to use a real tandem and real

hill (instead of a theoretical simulation) to develop test #4. As a starting point he sent a 400-pound test

team and instrumented tandem to Blankly Hill to obtain some real world brake force ratings. In the

meantime, the Avid spec for Cannondale tandems is on hold. While Cannondale's Product Team would

undoubtedly like to see the Avid brake re-qualified, Mark fully realizes that because Avid has not

approved their disc for tandems, Cannondale will be forced to accept a higher degree of responsibility for

any liability claims and/or CPSC recalls that could occur as a result of incidents where inadequate

braking is alleged.

P.S. As the concluding chapters are not less technical, you might consider printing or archiving this

multi-part post so that you can re-read it in its entirety. And in case you're wondering, because all of

these installments were completed before the first one was posted, a planned follow up post will (in a

week or so) address the unanswered questions that are bound to be raised.

Part 6: Is Santana's test too hard?

For years Avid had advised builders, dealers and customers not to install their disc brake on a tandem.

When we tested the brake, we agreed. Our tests confirmed rapid fade to ineffectiveness, melted

components and the occasional warped rotor.

Yet here on T@H, even before Avid relaxed its position, you could find the following kinds of posts

(paraphrased from memory).

Paraphrased post #1: "I've been using a rear Avid on my recumbent single and am totally satisfied. I don't

care what they say, if I owned a tandem I'd install an Avid on it."

My comment: Some people skipped Physics. Tandems are, on average, twice as heavy. Because of a

superior weight-to-resistance ratio, on steep hills a tandem can coast 40% faster than a single (and

probably 20% faster than the typical recumbent). Because a twice-as-heavy bike travelling 40% faster

has four times more energy (essentially the same as "Energy equals mass times velocity squared") a

tandem brake will need to create (and tolerate) up to four times more heat than a well-designed brake for

a single bike. Imagining that a brake will work on a tandem because it doesn't fail on a recumbent is

imprudent.

Paraphrased post #2: "Instead of Santana's contrived test, our company performed a real-world test. We

gave an Avid-equipped tandem to a local team that wins races. They rode it over a big mountain. They

told us the Avid performed great."

My comment: From the "wins races" description we can imagine that the testers were (1) lightweight and

(2) fearless---qualities that won't generate downhill heat. As for the test course, we don't know if the

descent was particularly steep---or even twisty enough to require constant braking. Although this

builder's post included a phone number, he did NOT add, "Operators are standing by to accept your

order." Because buyers of expensive tandems want disc brakes, every tandem builder (including Santana

and Cannondale) has a built-in incentive to avoid meaningful tests. Is Santana too prudent? Or are other

builders too eager to take your money?

Paraphrased post #3: "Our 310 pound team regularly descends a local hill and uses the Avid to scrub off

over 30mph of excess speed before diving through a corner. After maybe 20 repeats, we haven't even

needed to replace the pads."

My comment: A repeated test at a moderate level should not fail any brake. In fact, the original Mafac

rear brake on my first tandem would easily pass this test. While numerous decelerations from 50 to

15mph might seem impressive, a demonstrably tougher test would be a single emergency stop from

50mph. I know from controlled test results that an Avid disc brake will not be able to stop a 400-pound

team from 60mph. How do I know this? In a bench test performed at Cannondale, a strong one-hand

brake application through a standard lever and cable caused an Avid brake to fail from excessive heat

within five seconds. In Santana's test, where the speed never exceeds 15mph, the Avid performs much

better (and survives a half mile of 15% descent with two stops before failing).

Paraphrased post #4: "My Avid brake performs great. With a 100 pound stoker we can skid the rear tire."

My comment: The reason for putting a disc at the BACK of the tandem has little to do with braking

power. Further, when a powerful front brake is applied simultaneously, a rear skid (even with a heavy

stoker) can be a misleading indicator of disc brake performance.

Confused? It's easy to confuse stopping power with performance. While a stick through the spokes, for

instance, creates awesome stopping power, the modulation leaves something to be desired. A heavy

tandem team that will never leave Florida may need a more powerful brake (to avoid inattentive drivers

turning left), than a lighter team that lives in Switzerland (where drivers pay attention). While the Swiss

couple should also want stopping power, a more pressing need for tandeming through the Alps is heat

dissipation, a quality not needed in Florida. Ignoring extreme cases, the best answer for the average road

tandem team is a powerful brake for emergency stops, and a heat-resistant brake for steep descents.

While the powerful brake MUST be in front (where 80% of your emergency stopping power can be

generated), the heat dissipating brake is equally effective at either end. And though many tandem riders

have come to love their "drag brake," if your heat-dissipating brake also has adequate efficiency

(hydraulics and larger rotors both help) you'll need only two brakes to descend the longest and steepest

hills without a hand cramp. If you've followed the logic thus far, you may now realize that the most

efficient tandem set-up will be a powerful rim brake up front and a heat-tolerant disc brake in back.

Final Installment: Why not put dual discs on a road tandem?

While those who want a flashy tandem will continue to mount discs to the front of a road tandem (I

should know, my original tandem has sported dual discs since 1975), the resulting tandem will be less

efficient in 8 ways. Before listing the problems, let's review the physics.

Most bicycle enthusiasts approach this issue based on their knowledge of cars and motorcycles. If the

best cars and motorcycles have all switched to discs, they wonder, aren't discs an inevitable step forward

for bikes?

Maybe not. Over the past 30-odd years cars and motorcycles have evolved from (smaller) drum brakes to

(larger) disc brakes. The best bicycles, however, have always relied on rim brakes. And, when you think

about it, a bicycle's rim brake is a disc brake. That's right; those normal-looking sidepulls, center-pulls

and V-brakes have always been disc brakes. More important, the rotors (or rims) are relatively large and,

therefore, extremely efficient. As crude as they seem, on a pound-for-pound basis your bicycle's rim

brake system is more powerful than the disc brake system on your car.

But on a bicycle, isn't a disc brake more powerful than a rim brake? No. With the same amount of hand

pressure the rim brake provides more foot-pounds of braking force.

How can that be? Because stopping power is a squared function of braking radius, an 8-inch rotor (with a

braking radius of just under 4 inches) is a poor match for a 700c front rim (with a braking radius of over

12 inches). Here's the math: Since 91mm squared equals 8,281, and 311mm squared is 96,721, a caliper

pinching a 700c rim can produce nearly a dozen times more stopping force than an identical device

pinching an eight inch rotor. While bicycle disc brakes have come a long way (and are improving at a

rapid pace), today's disc calipers have not yet overcome this 12x disparity.

On bikes with 26-inch wheels, however, the rim-to-rotor advantage drops to 9:1. This, plus the difficulty

of mating rim brakes with suspended wheels, helps to justify the installation of front discs on mountain

bikes, where mud is a major consideration. Disc brakes on road racing singles? Don't hold your breath!

Because disc brakes LOOK powerful and high-tech, many enthusiasts dream of a tandem with dual discs.

While I whole-heartedly agree that a capable REAR disc is an immense step forward (at least for

moderately heavy teams that will venture into the mountains) a road tandem with a front disc brake will

suffer 8 inefficiencies:

First, unless the team is very light, today's discs aren't powerful enough for the front end of the tandem

(where 80% of the tandem's emergency braking power must be generated). Second, the bike will need a

wider fork or a weaker dished front wheel. Third, in either case the fork will need to be considerably

heavier (80% of your tandem's stopping power will be applied to the base of one fork leg). Fourth, the

heavier (probably steel) fork will be less comfortable than today's carbon forks (carbon can't tolerate the

heat of a tandem's disc brake caliper). Fifth, the wheel (dished or not) will need a heavier hub. Sixth, the

disc brake itself is also heavier. Seventh, if you want a sweet-handling bike, hanging an extra pound of

weight on one side of your steering axis won't help (an asymmetric application of braking torque won't

help either.) Eighth, the dollar cost of the previous inefficiencies is over $300.

If, in spite of the above listed reasons, you still think a dual disk road tandem is cool, remember that the

only reason a road tandem NEEDS a disc brake is heat dissipation, a function that can be performed by a

lone disc at either end of the bike.

PS: Our next round of tests will include the newest Gustav-M with 190mm rotor, the new version of the

Hayes mechanical (with caliper cooling ports), and an Avid mechanical disc mated with a refined 255mm

(10-inch) wave-rotor produced by Galfer. Send an email if you'd like to attend!

PPS My first twofer (bought used in 1965) was a short-coupled T. Parsons British road-racing tandem

that still wears silk sew-up tires. The dual discs I later installed were way cool. A cable from one Campy

brake lever controlled a finned aluminum master cylinder mounted to the frame via special braze-ons. A

pair of clear hydraulic hoses (with bright PINK fluid) ran to either wheel, where massive Hearst-Airhart

competition go-kart calipers (also finned) clinched stainless discs mounted to custom chromed hubs.

PPPS: And when I needed to stop in a hurry, the other Campy lever worked a front rim brake!

D. Bettge; letzte Änderung: 10.11.2003

Thanks Matthew - that is a great, really comprehensive article which fits with what I have read elsewhere on internet.

The most heat proof mechanical calipers are the TRP (non SLC) spyre & Bengal calipers. If using hydraulic, needs the bigger 4 pot calipers,  ideally.

I am afraid that post is at least 20 years out of date, much more recent strings on here have covered disc brakes to death.  Santana fit and market 10 inch rear discs, it's simply the best brake I have ever used on a tandem.  Twenty years ago there were problems, Phil Wood and Swallows with hope mechanicals had some well publicised and discussed (at the time) problems and legal cases.  As Arai ceased production the drag brake is effectively dead, but I would always want a 3rd (rim) brake in addition to twin discs on a tandem.  You pay your money and take your choice as with all things, but only drum brake can be used as a drag brake without problem.

 

Ps. According to American Tandem Club chat pages the Bengal pads have been found to demagnetise and fall out under extreme heat in mountainous country.  I used the TRP HyRd with 10 inch Santana rear disc.  Several descents of Col de Madeleine with 30 stone crew and no problems with the caliper, but TRP state it is for solo use only.

As Avid BB7s are still standard fitting on a large proportion of UK supplied tandems, I feel that article is still very pertinent. 

Agreed that 10" rotors are gold standard,  but not so easy to source aftermarket for a non Santana....

Well...... After a hard day examining lifting machines..... I open my emails to be faced with plenty think about on the tandem disc brake subject..!!

Thanks all for the info.... 

Whilst I found the long 2003 report interesting I'm a believer in "less is more" when it comes such reflections.......left me a bit dizzy..... .... What I got from the authors long  reflection as a cyclist new to tandem riding was.......Don't take brakes for granted on a tandem...! 

Given the fact I'll be riding in the hills more often than not I'll be installing a rear rim brake...... And reading more to ensure I have a disc brake set up that is known to operate well in the hills even with luggage

David

 

I don't think tandem manufacturers would be fitting parts to their bikes unless they were confident that they would be fit for purpose, the legal implications if a part were to fail would be huge, also trying to find tandem approved parts is extremely difficult (who is using tandem rated tyres for example) Frame and fork manufacturers will specify maximum rotor size, would the Santana 10" rotor even clear the rear frame on most bikes ? We are running Hope v4 with 205 vented rear rotor and have had no problems so far.

 

Well I did say it was an old report. Things may now be much better but it showed the sort of scale of the problems. 

Just another thought. The the Arai drums are no longer available but Sturmey Archer 90 mm hub brakes are available and could be used in a front wheel as a drag along with a rim brake for urgent stopping. 

I would also recommend the Rigida Andra Tungsten Carbide impregnated rims for any use where the rim brake is going to get heavy use. I wore out the first rear rim on my solo in just over 5 thousand miles riding in filthy conditions & all weathers. I replaced it with the Rigida Andra TC rim and it is still in excellent condition after a further 30,500 miles in similar conditions. The front one that was replaced later has now done 27,000 miles. I did put one on the back of the tandem but we had to give up tandeming because of my wife's hip replacements so that was still in excellent condition when we passed the tamdem on but I don't know how many miles that has done. I got those rims from SJSC.

I am not aware that there has been significant progress over the last 17yrs with regard to mechanical tandem brakes. 

Hydraulic brakes have progressed a lot, but afaik only designed for solos

The silver lining is the advent of E- bikes; heavier bikes designed to cope with some speed plus heavier riders.  Brakes for these bikes may have the possibility to transfer to tandems ....