cyccommute 

While I agree that trying to keep the speed to 25 mph, a disc brake should handle the heat issues far better than a drum brake does. Drum brakes tend to “pack” heat and eventually fail because they simply can’t take more heat. The disc brake sheds heat far easier than a drum. A rim…which is really just a very large rotor disc…sheds heat even better because if its size and area.

You do seem to have a rather low speed limit for a heavy bike on what you describe as steep descents. Having seen the pictures of your bike, it should be able to handle far higher speeds without issues. Perhaps you need to explain to your wife what keeping the speed down at such a low level is doing to the components of the bike. Ask her to let you run a little faster…10 mph wouldn’t be that much more and would be easier on the brakes.

You’ve describe “black gunk” on the brakes. Is that just brake dust? You might need to replace pads more often given your brake usage but that shouldn’t necessitate a brake bleed nor should it cause much problem with the caliper. If you have oily black gunk, that says something is wrong with your caliper. You shouldn’t have anything oily around the pads or the caliper or the rotor.

fooferdoggie 

I just lost my bravery over the last year so no fast speeds.most of the roads we go down you cant just let go 25 or 30 is often the speed limit. we are in the city not out on a mountain. like this is the most we have descended at once https://ridewithgps.com/routes/36746676 I need to use the back less and I will work on that. the rear rotor would have hardened black gunk on it. most likely brake dust and from the rotor getting too hot. the braking would get worse and worse till I cleaned it off. alcohol if that did not work sanding.

Carbonfiberboy 

Experience rules here - Arai drums simply don't fail, discs do. There's the famous tandem group descent of Mt. Ventoux where the only bikes to make it down undamaged had rim brakes or rims plus drum. That was years ago though and discs have gotten a lot better since then. The secret to long descents with rim brakes is to stop and let them cool if you start to feel them fail, i.e. brake lever pressure increases. With either rims or discs, the thing is to alternate brakes and use hard, brief pulls on the levers.

It's not the components so much as that overheating the brakes is extremely dangerous, i.e. you can die..

Carbonfiberboy 

IMO steel beads are worse because of what you say and because the steel holds the heat in the bead and could thus soften it.

jccaclimber

With all of this conversation about bead expansion, I wonder if the aluminum rim expands faster than the bead does anyways? As a bare material it certainly does, I'm just not sure what it does as a system given the spokes, and I don't really feel like putting it into APDL to find out.

IME a third brake wouldn't be a bad idea. If nothing else it's a handy backup in case one of the other two ever fails. I don't see a situation where used responsibly (IE, it's not a true drag brake like an Arai, and the stoker doesn't use it without coordination from the captain) that an extra rim brake would not be better than an equivalent disc brake bike without it.

Carbonfiberboy 

My friends' tandem which went off into the blackberries got exactly that addition after their scare. Only problem is that stoker has a tendency to use it without telling the captain, not good.

fooferdoggie 

we only had some brake loos when the had the cheap two piston 180mm rotors. but I need to control the heating more. its going to be awhile before we can really test the better braking my wife needs a shoulder replacement surgery so she cant use both arms to help climb an once she gets surgery it will be unto 3 months before she can ride again . So now I need a way to haul her around she hates being house bound.

jccaclimber

I'll phrase this differently. I see this as two separate things.

1. Does an additional braking surface provide additional braking capacity, either in stopping power or in heat capacity?
2. Should stokers have brake control?

You can change the first without changing the second. The OP in this case has already concluded that they want their stoker to have a brake. I think it's generally against best practice, but we've already voiced our opinion on that. At this point all we can do is educate on what might go wrong, and in what circumstances. The OP can then choose to accept those risks and/or avoid them.

Personally, while I generally advise others not to give the stoker brake control, I do let some of my stokers have control of the drum brake. I find it handy when riding around my house. There are a lot of steep downhills with stop signs and then short flat sections at the bottom before the next downhill. I also only do this with the few stokers that understand the ramifications of unexpected braking on my ability to keep them off the pavement. For others I disconnect it and change my route or behavior in a way that makes it unnecessary.

fooferdoggie 

my wife only brakes when I tel her to so its not a real problem. its how we learned to ride the tandem since the bike came that way. I just tell her to brake and how hard. before the brake upgrade she had to use that brake when going on steep slopes because the discs were not strong enoug and we literally could not stop without her brake.

dabac

I’ve seen spinning bikes using v-brakes for their resistance adjustment. With some textile/fibrous pads. Maybe such pads would make it possible to use a v-brake as a drag brake?

Leisesturm

Some people call the brake handle between the drivers and passenger seats in most cars an 'emergency brake'. It's actually a 'parking brake' and quite useless in a real emergency. Don't be taken in by Hollywood! Even in those accidents where brakes have failed, especially the ones where investigators found the brake pedal fused to the firewall from the force of the drivers foot given superhuman strength in their panic. In not one of those fatal crashes did the drivers ever try and use the parking brake. When you need to stop, you usually need to stop. NOW. And by using the motions built up through practice and only those motions! There isn't any chance to call for more brake from the back or passenger seat even if there was some there! Either it makes no difference to the outcome (wasn't necessary) or you crash because the primary brakes were insufficient. I haven't personally found found that a single front brake isn't enough for a wide variety of stopping situations. The rear brakes on all our tandems aren't up to much! The primary commuter had the rear brake out for months and we did just fine.

Giving the Stoker control of a proper drag brake is a time honored tandem practice. But it isn't the only way, or even the best way to do it. We briefly owned a Burley Samba with an Arai drag brake. It was set up with the drag on a thumb shifter on the left hand side. We never got to really try it out but I got the idea of how it works and I can't see why any Captain would feel the need to hand off that particular assignment. Stoker appeasement must play some part in things. Some tandem couples think its because my Stoker is blind why I get away with the crazy descent speeds we use when we've been on outings with the tandem club. Nope. 'J' is pretty well aware of how fast we are going and it's TRUST that if I didn't think 45mph was a safe speed for a straight line downhill with a wide shoulder then I wouldn't do it.

The o.p. and his Stoker are a relatively young team in terms of riding twogether. I find it problematic that they found twin piston 180mm discs were so insufficient that they went to four piston 203mm and are still underwhelmed. We are agreed that a v-brake cannot be used in true drag brake fashion where the brake is applied via a thumb shifter, NOT a brake lever, and it is not released until the descent section levels off. There would be plenty of time to warn the Stoker of the upcoming downhill and then tell them to release. The v-brake would need much different management and only the Captain could know how hard and when. It simply is not possible to communicate the finesse of it verbally.

It would be better, I think, to use the v-brake as the primary rear brake (it's been done!) and put the 203mm disc on a thumbshifter and use that as a drag brake. I'd still want to have control of it, but in a scenario like that I wouldn't have too much misgivings about letting the Stoker play with it. I keep my Stoker entertained by letting her navigate. As I said, blindness does not prevent her from knowing exactly how fast we are going, and on a club ride she is about as good a GPS as there is. In town she is even better. She rarely misses a turn. No car has ever been set up with dual controls except the Student Driver jobs. Even so. People have been taught how to drive in standard cars where the instructor had no override. No wonder it usually goes so badly. As I write this I am recalling that only a couple of months ago a student pilot and his instructor were lost in a fatal crash of their Cessna. Dual controls? Absolutely, but the scant microseconds it must have taken for the more experienced pilot to perceive danger and intervene were not enough. Some things you need to stay on top of to stay safe. I'll leave it there.

fooferdoggie 

the brakes that came with the bike were a step below deore calipers. when we went off-road you could not come close to locking the rear up even going 10mph or less . I found you cant use much front brake when going off road or the front will slide out while turning. we have several 20% grades we go down. in that case to stop my wife had to use the v brake. Now I want her only using it so I don't overhear the back disc. I can stop just fine without it. she only brakes when I tell her to and how much I tell her and its never been an issue. it has not caused control issues. I don't rely on her using the v brake to stop us in an emergency she uses it so I can let the other brakes cool. neither one of us wants to go faster and often the roads are posted only 25 we are in the city for the most part.
this is a sample of one of the hills no way the old brakes would keep the speed we need on this hill with a road crossing right at the bottom. . seldom do we have a clear road with no cross streets. the v brake only has about 1/2 the stopping power of the disc but it actually does pretty well. I think she does very well with it and it has never caused me to loose control or even have any issues at all. its just a tool for us. she only uses her brake on long descents.

Leisesturm

That looks like fun actually, whee ...

jccaclimber

Unfortunately not the same thing. The problem isn't pad failure, the problem is heat dissipation. The spin bikes have a large heavy rim with a lot of surface area and no rubber to worry about. Bicycle tires have a small light rim with less area to shed the heat.
I wouldn't be surprised if the spin bike pads also require more cable tension for a given amount of stopping power. They only need to be able to handle what a person can generate. A bike descending a hill, especially a tandem, needs to dissipate substantially more energy than a person puts out on a spin bike.