Brakes with heat capacity

[martinf]

>Thanks, yes, keep the disk. I'm thinking to use a Sunrace M90 Friction Thumbshifter for drum control.
>The lever would not interfere with other controls. Perhaps I could "set" it on steep grades without my thumb having to hold it.

Done that. It worked for me on the rear brake.

When I had a tandem in the early 1980's, it came with front and rear Mafac long-arm cantilever brakes and an Atom rear hub brake.

The original levers (for drop bars) were one ordinary and one dual-pull. It was a long time ago, but I think the dual pull controlled both cantilever brakes.

I didn't like this arrangement at all, and very quickly changed it for two ordinary brake levers, one each for the front and rear cantilevers. I also changed the rather mediocre Mafac brake pads for Scott Mathauser pads, which were much more effective. The cantilever brakes were then sufficient to stop the tandem quickly, but having burst a tyre on a solo due to rim heating on a long, steep and slow descent I appreciated having the additional big drum brake on the rear wheel to shed heat away from the rims.

I used a Suntour ratchet-type thumbshifter to control the hub brake. Which I used mainly as a drag brake on longish hills. The ratchet allowed me to keep the brake applied without having to keep a hand on the thumbshifter. I didn't want to have a stoker controlled brake, especially after I converted the rear of the tandem to kiddycranks for my children.

At that time I had a job driving buses, some of which had Telma electric retarders, which worked in a somewhat similar way. So on the tandem it was reasonably easy for me to apply the "retarder" and remember to remove it when I needed to stop braking.

This arrangement meant I could keep my hands on the levers for the cantilever brakes most of the time, ready to do an emergency stop without having to think about the hub brake.

[mickeg]

..., yes, keep the disk. I'm thinking to use a Sunrace M90 Friction Thumbshifter for drum control. The lever would not interfere with other controls. Perhaps I could "set" it on steep grades without my thumb having to hold it.

I would not want a friction lever for a front brake, that is your steering that you would lose if you locked up the front wheel.

Maybe I am being tooooooooo cautious here, I have not ridden on a tandem and have not had the experience that you do.  Perhaps two riders on the bike puts enough weight on the front wheel that it could never lose traction, but I can think of times when a front wheel on a solo bike has slipped from sand on pavement or wet conditions or something else.

If I am being too cautious here, please tell me.

[Danneaux]

If I am being too cautious here, please tell me.

Some caution is good here, in my experience.

I've owned my tandem for 30 years and I've upgraded it periodically. I bought it used and started with it as-configured with comfort handlebars and the left brake lever controlling both cantilevers and the right lever actuating the Arai drum/drag brake alone. I didn't like it much. Having two cantis on one lever allowed for balanced braking if I used the adjusters on the cable stops but I missed being able to individually control braking, especially as I use the front brake some 80-90% of the time. I found actuating the Arai as a standard rear brake didn't really stop the bike so well for me even though it was virtually new, along with the rest of the bike.

I promptly converted to drop handlebars for captain and stoker and revised the braking so the left lever controlled the front canti, the right lever controlled the rear canti and a SunTour ratchet bar-end shifter controlled the Arai so it could be set solely to work as a drag brake. This was an immediate improvement, so based on that experience, I swapped out the original Dia-Compe cantis for some Scott/Pedersen SE (self-energizing helical cam) cantis at the front and rear. I have these on two of my singles and despite being very fussy to setup and what many people regard as an excessive "off/on" feel, I like them...primarily because they require less hand effort to actuate and are very powerful if setup correctly. Once the pads contact the rim, they are drawn forward and inward by friction with the sidewall, causing a sort of "power-assisted braking" effect.

With this last setup, I felt secure on 101kmh/63mph un-moderated downhill runs. If I set the Arai to drag, my speed could be held to about 67kmh/42mph, well within the range I felt my Scott/Pedersen SE cantis shod with Kool-Stop salmon pads could handle for a quick stop two-up but sans full touring load and added trailer (which alone can weigh 56.7kg/125lbs as it is sometimes full of 26.5l of water and extra food for desert touring). When my sturdy Dutch touring buddy came for a visit we took everything including the (folding) kitchen sink and the loaded bike, trailer and both of us together weighed in at about 272kg/600lbs. I had no trouble stopping the train in pretty short order on downhills, despite being shod at the time with 1.6in road slicks. The one time I had doubts, I was booming downhill in town at just over 100kmh and the red traffic light at the bottom unexpectedly turned red and a truck immediately pulled out. I was able to stop in time but admit to having some doubts. The Arai was really, really hot afterwards as I employed it just before squeezing the brake levers so I had everything in play.

The tandem's long wheelbase -- and the weight of a stoker on the back, plus whatever additional gear or trailer you might have -- prevents pitchover and unweighting of the rear tire to a much greater extent than on a single. However -- and here's where I get to George's question -- front braking really shines in the dry and on good surfaces because there is no danger of going over the handlebars. The limiting factors are instead tire:road traction and fork rigidity/resistance to shudder. I have found under heavy front braking while heavily loaded, the locked front wheel made dot-dash skid patches on dry, smooth pavement as the fork cycled under load and the tire briefly lost traction then regained it. It is a little disconcerting but I found it to be controllable in the dry. In the wet, however, it is pretty treacherous and there is no way to achieve such high levels of braking without the front tires skidding on pavement and this could lead to the front tire washing out and a fall. Levels are even lower on dirt or gravel.

My current iteration has me running Deore v-brakes and compatible drop-bar levers with Andra 30 rims and 2.0in Schwalbe Duremes. Though the Duremes are not road slicks, their greater width/volume/cross-section (and lower pressure) result in superior tire:road friction and have pretty much solved the dot-dash braking and fork cycling; the bike just stops more quickly than with the older SE cantis and 1.6in road slicks. Braking force seems to be a little better than my best Scott-Pedersen SE canti setup. Mechanical connection to the road is so much better and rim braking improved enough I find myself rarely using the Arai drum/drag brake these days.

I can't possibly give an estimate of a minimum stopping distance from a given speed as I am usually pretty busy at the time. I will say the sensation of stopping (g-forces, load on hands under braking) feels greater than on my singles for a given speed because I don't have to worry about pitchover under hard front braking. However, I cannot imagine anything so heavy as a loaded tandem being able to stop as quickly as a loaded or unladen single, but...maybe it could! I have no idea and the number of variables in play is staggering.

My next development will be to modify the rear dropout spacing to accept the internally-shifted Rohloff hub so kindly gifted me by a friend. This will involve me machining and brazing in spacers to the inside of the rear dropouts and appropriating the Arai PacMan mount I had previously relocated from atop the left chainstay to the bottom to use as a new locating point for Rohloff's long torque reaction arm. This will mean no drag brake of any kind, so I will depend fully on the Deore V's with Kool-Stop pads on the Andra 30s for braking. Experiments show it working reasonably well so far from pretty high speeds. As for the drivetrain, the cabling is currently internal for the front and rear derailleurs and the Arai. The new cabling will include two cables for the Rohloff and one for the front mech, which I intend to keep for two close-ratio chainrings to allow a wide enough range (within Rohloff's stated low ratio while allowing an "overdrive" at the upper end. All ratios will be duplicates except the four at either end so I can choose between ranges depending on terrain). The existing rear mech will be used as a tensioner because the bike uses vertical dropouts and the only eccentric is used to tension the timing chain so the rear derailleur will take up the slack on the Rohloff's drive chain. All this is less than ideal but I like and am attached to the bike which works well. Its aging SunTour Accushift 3x6 drivetrain is growing tired and I have only one new freewheel left to swap in. I'll probably run that out before making the swap to "hybrid" Rohloff. I'm looking forward to the Rohloff's shift-at rest feature on the tandem as I use it a lot when when starting from a stop on my Nomad.

Best, Dan.

[martinf]

This is theoretical, as it has been a while since I had a tandem.

I reckon properly set up modern rim brakes are good enough to stop a heavily loaded tandem reasonably quickly, as Dan has said the limiting factor is tyre adherence so care needed, especially in the wet or on gravel patches, diesel oil spills, etc.

The problem is heat dissipation on long hills, for which the ideal solution is IMO a drum brake that can be run hot without affecting the grease in the wheel bearings or (theoretically again) expansion of the hub shell affecting spoke tension. The latter could have been an issue with my Atom drum brake, but I never got it hot enough to find out.

The most suitable drum brake for this used to be the screw-on Arai, nowadays the closest alternative currently available that I know about is this Karasawa brake from SJS:

https://www.sjscycles.co.uk/brakes/karasawa-screw-on-tandem-drum-brake-replaces-arai/?geoc=FR   

Which will fit double-threaded derailleur type hubs (if these are still available, not searched) but not Rohloff. There is also something called the "Maddox drum brake", but I don't know if it is available or not.

It might be possible to fit this brake to a modified solo rear hub to use on the front, if the fork spacing is sufficient and, very important, if the fork is strong enough. If this is possible, it should be better than a Sturmey-Archer drum brake for three reasons:

- it would allow the use of a hub with a stronger axle than the Sturmey-Archer front drum hub.
- it has a larger diameter, so should have more braking power. It is also quite heavy (850 g according to SJS) so it should absorb a reasonable amount of heat.
- because it screws onto the hub, heat transmission to the wheel bearings should be less.

I don't know the weight of the Arai hub, but with its cooling fins it was probably a bit better at heat dissipation than the Karasawa would be.

For control of a front drum brake I would prefer an additional lever on the same side of the handlebars as the lever for the front cantilever, maybe under the top of the drop handlebar. This would not allow simultaneous use of the two front brakes, but it would enable finer control. I don't think I would be comfortable with my ratchet thumbshifter solution for a front brake.

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Other possibilities:

1 Upgrade the rear disc brake to the 10 inch Santana, which is designed specifically for tandems. it appears to have cable control rather than hydraulics. This might mean modifying the rear triangle to fit a compatible brake mount, and probably getting an adapter made to fit the rotor to a Rohloff. And it probably wouldn't be quite as good as an Arai for heat dissipation.

2 Maybe try and get an adapter made to fit a Karasawa or Maddox drum brake to the Rohloff disc mountings. Santana seem to have one for normal disc mountings:
look for "Drum Brake Mount Convert disc flat plate to Arai or Maddox drum brake" in Google.

For a (very theoretical for me) tandem in 2022, personally I would prefer one of these two solutions to a front drum brake.

[Andre Jute]

Considering the effloration of rear frame-end spacings we've seen in recent decades, I really don't understand why the tandem drag brake, and other high speed braking  problems in loaded touring, are not solved by ventilated discs, as on racing and other fast cars once the optimum disc diameter or rim diameter limit was reached. If frame-ends can be spaced out for a Rolloff, for wide tyres, for whatever purpose, why not for a brake with double the cooling and thus substantially more braking power? A 200mm ventilated brake would be a very powerful animal indeed, and would be able to dissipate enough heat to allow for twin callipers if the tyres have grip beyond what a single calliper can turn into retardation, for it is always the friction at the tyre/road interface which determines braking power (given that weight transfer has been taken care of).

Sorry, this doesn't do anything to solve Hendrich's problem because his bike is built, and he must start from where he has arrived...

[mickeg]

I want to thank those of you with tandem experience for educating me on some of the aspects of tandem bikes.  I have learned a lot on this thread.

[hendrich]

Thanks to all for the great information. Not sure what my decision is yet, but I have a better appreciation for Thorn's adoption of the Hope ventilated disk for Rohloff. I may go that route and deal with removing the caliper and coiling up the hydraulic line each time I break the tandem apart.

[Danneaux]

A bit late in the discussion, but this link may prove directly helpful...
https://www.cyclingweekly.com/news/product-news/is-heat-build-up-in-disc-brakes-something-to-worry-about-310878

Best, Dan.