mtseymour

Skill is always much more important than equipment. I have no doubt that a skilled tandem team can safely descent Mt Ventoux on caliper brakes. Or poor technique can oveheat the most powerfull hydraulic disc brakes (on bike, car, or motorcycle).

In one Grand Fondo, I saw a multi-rider crash just a few km from the start line. Riders were on the ground and one frame was broken into several pieces. it was a flat, smooth road in dry condition. There was no reason for these riders to crash but one over-eager rider found a way to trigger the pileup. In mtn bike races, it's not unusual to see a pileup at the first mildly technical descent. It wouldn't surprise me if one of these riders blamed the crash on equipment failure.

I don’t mean to de-legitimize safety fears, but car, motorcycles, and mtn bikes have been using hydraulic brakes for million of miles because they provide more safety at high speeds. There is no shortage of empirical data that hydraulic brakes are superior. Nevertheless, we have lawyer tabs on dropouts and safety warnings on ladders because there's always one person who defy common sense. Every crash with an injury that someone has blamed on a disc has been more or less been proven to be something else. The Bike Rumour article by Tyler Benedict is another example of a sensational headline disguishing poor component choice, installation and technique.

pdlpsher

You are forgetting that there's traffic (both vehicle and bicyclists) on popular routes. A descent like Mt Ventoux can easily be limited by traffic and not rider skill.

Recently I climbed to the top of Pikes Peak and Mt. Evans on my single bike. On both descents I was forced to push my brakes to the extremes due to 1) heavy vehicle traffic and there's simply no way to pass on the switchbacks, and 2) there's simply not a whole lot of air at 14,000' to dissipate the potential energy. Even with the best equipment I highly doubt a tandem could safely descend both mountains unless they stop after each switchback. I wouldn't call this an outlier condition. On these popular roads tourists take their time going up and down. They are not rushed and they don't really care if our brakes overheat.

Simply blaming the rider for his lack of skill is wrong.

stevoo

I have boiled fluid on two systems.
Formula hydro 100% failure at 61 mph road tandem. Not good!
Also old Hope 4 pistons on mtn tandem. Also not good coming down Columbine at Leadville.

Both designs have incorrect pistons that do not keep the heat from getting to the caliper body.

Modern designs have addressed this.
Hope now uses phenolic pistons and Shimano ceramic pistons.

Crazy that bike industry did not learn from motorcycle industry early on. They figured this out eons ago. Guess they had to reinvent on their own.

Happy now with Shimano Zee on mtn tandem and Shimano also on road as well as a custom BB7 set-up on other road.

Can even run sintered metal pads with the correct new systems. Life is good.

FBinNY 

Not disagreeing s much as reminding that part of "skill" includes understanding the limits of your equipment.

Brakes adequate for long, steep descents are possible, but most folks wouldn't want the weight penalty. For example we could use double thick rotors, or add mist cooling systems. But short of a complex and heavier brake system, we're at the mercy of the basic physics. Resisting gravity through friction produces heat, and that heat has to go someplace. It's all about weight, grade and time.

pdlpsher

I simply want to remind everyone that braking limit is not all about a team's weight, disk rotor size, and mechanical vs. hydraulics. External variables such as traffic, wind direction, ambient temperature all can stress a braking system to the limits.

It would be wrong to assume a braking system is adequate without taking into account all of variables, including those that are completely out of the team's control (traffic and wind direction). Descending with a tailwind can put stress on a braking system. Likewise descending from 14,000' elevation is not the same as descending from 4,000' elevation.

loopless

Just to add for disc brakes - I think it is also relatively important to ensure your brakes are properly tuned in and cables tensioned proper.

saying this as my new bike started losing braking power and it was only after a 30day tune up did i feel the amazing power of disc braking.

cheers.

79pmooney

You could do what we did to ride out storms when we sailed the Atlantic - trail a long rope. We trailed several hundred feet with each end tied to the rear corners of the boat. You would have to make sure those pesky singles always looking for a ride stay well off your wheel. A car running over the rope would provide a little more braking power than you want. (We saw one ship and one plane, both at great distance, when we were in deep water. Getting our rope run over wasn't an issue.) Trailing a chute from sailboats is considerably more effective than towing rope, but more prone to failures. But for a bike, effective keeping those singles away and cars are far less likely to run over it.

Ben

FBinNY 

The friction afforded by trailing a rope is nothing like the effects of pulling it through water. Plus to do anything, it would have to be too long which creates added danger.

I believe that a small drogue chute could be made, but it has to be designed and deployed correctly. A good one would spill air out the bottom, creating some lift and keeping it up and away from the rear wheel.

But, as has been pointed out, braking is adequate if managed well. If and when it isn't, the worst case would be having to take brake breaks from time to time. But it's still up to riders to understand what brake heating is about and how to manage it.

B. Carfree

This thread reminds me of a story told to me by the builder of my first tandem. He and a few friends had just returned from Lon Haldeman's cross-country "rapid tour" (across the US in two weeks) on a quad. The quad had two rim brakes and two Phil Wood disc brakes (google it; yes, this was 1988). Needless to say, four adults on an in-line quad descending any decent-sized mountain is going to be exciting, to say the least.

They settled in on a system of having two or even three stokers put "air brakes" in play when needed. Air brakes were wind-breakers deployed as parachutes (open the zipper, grab hold of the ends and raise one's arms). They would use that to get down to 45 mph, at which point the normal brakes would work fine without overheating. I've used that system a time or two myself when while touring. It's amazing how well it works at high speed.

diabloridr

Some friends were bikepacking in Peru and experimented with dragging a large branch behind their tandem for supplemental braking on steep, unpaved descents. I thought they had a picture of this get-up on their website, but I'm coming up empty.


It worked, but I noticed they haven't resorted to this technique since.

B. Carfree

Ha ha. Decades ago, the Sacramento Bee reprinted an article from the early days of cycling. It talked about touring on "ordinaries" (high-wheelers). In order to keep their speed down on long steep descents, they would carry a chain. Said chain would be used to attach a large branch to the rear of the bike as a true "drag" brake.

pdlpsher

With an e-bike some of the potential energy on a descent could be captured and used to recharge the battery.

Here's an interesting read. I subscribe to the German magazine Tour. It's a technically-oriented cycling magazine....similar to Consumer Reports but it's 100% dedicated to cycling products. They tested the previous version of Shimano's Ice-Tech 160mm rotors on a single bike and they failed spectacularly. The aluminum core that is sandwiched inside the stainless steel braking surface had melted and the disk collapsed. Recently they tested the latest improved Dura Ace 160mm rotors and the front brake also failed but it didn't collapse like the previous version. Their conclusion was that the new design was a significant improvement over the previous version. However they caution that heavy riders will likely push the new version to its limits. The test was done with a 220lb system weight (bike plus rider) with a 245 meters altitude loss at a 13% average gradient.

This goes to show how big of challenge it is to design a braking system that is both capable and light enough for every day use, for a single bike!

mtseymour

I think that your interpretation of these tests are alarmist and out of context. Let’s start by clarifying the German bike mag "Bike" did the brake tests. “Tour” is a sister publication and merely cited the “Bike” results. Delius Klasing is the publisher of both magazines. These magazines are not similar to Consumer Reports because they’re owned by a for-profit company and accept paid ads.

Unlike other magazines, Bike’s approach is to test these brakes in “extreme” rather than typical conditions. The testing was done at their Bolzano test track and on a “drum tester”. The test track is steep with an average 20% gradient and a 700 meter vertical drop. The 1st 300 meters is on mtn trails, with the remaining 400 meters on dirt or asphalt road. This translates into a 20% descent for 2.2 miles. They also use a drum tester to confirm their results.

The test that you cited was probably the 2015 test. Bike tested 5 lightweight “race” brakes: Formula R1, Hope Stealth, Shimano XTR Race M-9000, FSA K-Force, Magura MT8. They also tested 4 sturdier “trail” brakes: Magura MT7, Sram Guide, Formula CR3, Shimano XTR M9020.

Several of the “trail” brake were overheated and suffered warped rotors (eg. Sram Guide). The Ice-Tech rotor was partially de-laminated but didn’t “collapse”. Nevertheless, the brake was still usable and Bike concluded the Shimano XTR M9020, Sram Guide, FSA K Force were “Very good”. Only the Magura MT7 and Formula CR3 were rated higher at “Super”. None of the brakes were rated “Good”, “Satisfying”, “With Weaknesses”, or “Insufficient.”
In the 2016 test, Bike tested 7 disk brakes (Brake Force, Formula RO, Hope Tech, Magura MT5, Shimano XT BR-8000, Sram Guide, and Trickstuff) using 180mm rotors. Magura MT5 was rated “Super”. Shimano, Formula, Sram, Hope, Brakeforce, and Trickstuff were all rated “Very Good”.

So it seems the Shimano brakes and rotors were rated “Very Good”, and obviously superior to V-brakes and cantilevers. In fact, Bike stopped testing rim brakes after 2003, partly in answer to the question: “can rim brakes still keep up?” You can guess the answer.

The Bike tests were intentionally “extreme” to highlight fairly small differences between brands. Shimano and other hydraulic brakes are overbuilt for typical riding conditions. Their safety margin is more apparent when you compare the Bike test conditions to famous downhills. Using Strava ride data, you can see that the Bike test track is more than twice as steep as Mt Ventoux, Pikes Peak, etc. None of these challenging downhills have any steep sections close to 20%, and none have 20% sections that are 2 miles long.

The Strava data shows that more than 21,200 cyclists have descended Mt Ventoux since 2009, most of them probably using caliper brakes. There have been many reports of tandem teams using caliper, mechanical, and hydraulic disk brakes to safely descend Mt Ventoux.

The Strava data also shows a wide variance from the fastest time to the median time. In other words, the fastest riders were about 40% faster than half of the field. The gap increases to 80% for the steeper descents (eg. Mt Ventoux).

The difference in descending speed is due mainly to bike handling skills (eg. body position, looking ahead, picking good line, braking properly). Bike handling skills is just as important for recreational riders (eg. Century Rides) as elite racers when there are steep or technical sections. Riders like Froome can gain time on the descents by braking appropriately and getting more aero position (ie. sit on top tube).

Unfortunately, some tandem teams overheat their brakes by dragging their rear brakes and under-using their front brakes. Here’s one example:

“We climb a lot and a front disk is totally unnecessary. In fact, I only use the front brake if I have to make a sudden and quick stop. I don't even recall the last time I used the front brake. Because there's so much weight on the rear tandem tire, one cannot lock up the rear wheel. Using only the rear disk for braking is perfectly fine on a tandem...”

This method will unnecessarily overheat the rear brake, and lead to sensational postings about melting rotors. There are many articles that explain the value of brake modulation and using both brakes:

How to descend safely - BikeRadar
https://cyclingtips.com/2010/04/descending-tips/
https://www.bicycling.com/training/f...scending-hills
https://www.singletracks.com/blog/mt...mountain-bike/
https://www.sheldonbrown.com/brakturn.html

Still not convinced? Take your tandem to gentle slope and set up a start line to start coasting, and a line to start braking. On your 1st pass, coast from the start line and start braking at the brake line with your rear brake only. Mark where you finally come to a stop. Repeat this same procedure with just the front brake. Although a tandem is heavier than a single, it’s virtually impossible to endo when using just the front brake. On your 3rd pass, use both brakes at the same time. You should stop fastest when using both brakes, and slowest when only using the rear brake.

With proper braking technique, tandem shouldn’t overheat properly selected and installed disk brakes.

pdlpsher

mtseymour,

Once again, you have forgotten about the external variables such as vehicle traffic. The gradient and descent length is only part of the story. The reason why Tour do these tests is because these are not really extreme conditions. Have you personally descended on Mt. Evans or Pikes Peak? These mountains are open only for a short time due to inclement weather and the tourists jam pack the mountain on the weekends when the roads are open to traffic.

By the way, I have already stated Tour's brake test protocol, which is "The test was done with a 220lb system weight (bike plus rider) with a 245 meters altitude loss at a 13% average gradient." You went on to describe a different protocol which is not what Tour had used.

I have the Tour's test results but I don't plan on sharing it here because the publication is copyrighted.

mtseymour

You keep digging yourself a hole and don't know when to stop and listen. You can ride more safely and reduce equipment failure by using proper braking technique. Let's resume the fact checking.

"They tested the previous version of Shimano's Ice-Tech 160mm rotors on a single bike and they failed spectacularly. The aluminum core that is sandwiched inside the stainless steel braking surface had melted and the disk collapsed."

Neither Bike or Tour magazine said that the Ice-tech rotors "failed spectcularly", or that the disk rotor "collapsed". The grueling tests ended up with the Shimano XT brakes and Ice-Tech rotors receiving a "Very Good" rating, along with several other hydraulic brakes (eg. Sram Guide).

"Recently they tested the latest improved Dura Ace 160mm rotors and the front brake also failed but it didn't collapse like the previous version."

In 2017, Tour magazine did a "first test" of the Dura Ace R9170 disc brakes (w flat mount) and RT900 Freeza rotors (160mm) on a Pinerello Dogma with ZIPP carbon wheels. The rider and bike weighed 220 lbs (100kg). The test track was 13% for 245 meter drop, which translates to a continuous descent of 1.2 miles. The Freeza rotor has substantially more material for heat dissipation, but has limited use for tandems because of its 160mm limit and new flat mount. The Not surprisingly, the Tour liked the Freeza rotors and didn't mention any "failure". The video is a a bit mundane because the test rider completed the descent without any drama. My German-speaking friend was disappointed that there was no spectacular crash or failure in the video.

As for your excuse of "copyright" restrictions, the "fair use" rule allows anyone to quote copyrighted materials for limited discussion purposes, especially in a non-commercial setting. Without the fair use rule, we would not have a free press, internet forums, or academic research. So please show us the data or test summary!

I doubt that you can because the real problem is your braking technique. When discussing your new 2017 titanium Santana in this forum, you stated that

"Disk brake is imperative for our riding. We had a front tire blowout on a steep descent and that led to us to replace our 1987 Sovereign with a 2012 Team Scandium with a disk brake. We do a lot of climbing and with a rim brake the rim will also probably wear out very quickly. We use the rear disk brake 95% of the time. The front brake is only used when quick stopping is needed."

It doesn't make sense that you would buy an expensive titanium tandem (with ti bolts, no less), and then avoid using the front brake to avoid rim wear! This is a good example of misplaced priorities. By mainly your rear brake, you double your stopping distance and consistently overheat the rear rotor. This will lead to severe brake fade or failure just when you really need both brakes.

Here are two videos that show that simultaneous use of F & R brake is TWICE as effective as using just the front brake. The GCN ("Brake like A Pro") shows that a single bike using just the rear brake requires twice the stopping distance as a bike using F & R brakes:


Since a tandem is heavier than a single, the it's even more important to use F & R brakes. Look at this video of a motorcycle using only rear braking:


So stop blaiming the brakes and use them properly.

BTW, I've been skiing and mtn biking at Whistler for over 30 years. Doing 20-30% off-road descents is fairly routine around here. So a 7 or 13% road descent is fun but not particularly challenging, even when dodging cars and other riders.

pdlpsher

mtseymour,

Since you never answered my question I'll assume you have never ridden Mt. Evans or Pikes Peak. None of what you wrote address the main issue of dealing with the extreme braking conditions caused by external variables such as traffic. Several posts back you had said these 'brake tests' are too extreme and you called me an 'alarmist' for bringing the brake failure article into attention. I replied back to you letting you know you have forgotten about the external variables such as weather and traffic. You went on to say that today's modern disk brakes are safe and that the riders are to blame for improper braking technique.

As several others have pointed out, the disk brake has a limit in terms of how much heat it can dissipate. Engineers design a system that will meet perhaps 90% of the expected load because no one wants a disk brake that weighs 15lbs. The limits of a modern disk brake system is reached more frequently than you think. One forum reader posted their experiences on brake failure on Mt. Ventoux. When someone brings up their brake failure experiences you immediately blame them for improper braking technique.

I invite you to come to Colorado and do Mt. Evans either on your single or tandem. You could stay at my house and I'll be your host. Once you have experienced of going down a steep mountain with heavy vehicle traffic where your speed cannot be faster than 20mph, with an air density that is a lot less than at 4,000' elevation, you will understand that the modern disk brake cannot handle all situations safely as you claimed.

mtseymour

Thanks for the invite but I'll pass. I haven't done the Pikes Peak downhill and it's not on my bucket list. Although it's a long and grueling climb (partly due to high altitude), Mt Ventoux and the Alps are more appealing because of the scenery, fine food, and cultural attractions. As a downhill, Pikes Peak is fun but not difficult (compared to my prior descents). Mt Evans is even easier with an average descent of 4%.

The Col Collective posted a Youtube video of the Pikes Peak downhill. It has an elevation drop of 6,315' (from 14,115' to 7,800') over 19 miles. The average grade was 6.5% with short sections of 13%. Michael Cotty (a Mavic and Cannondale ambassador (and Col Collective cameraman) did the descent on a single with Mavic Ksyrium Pro Carbon clinchers and caliper brakes. The Mavic carbon clinchers can't match the braking ability of aluminum rims or disc wheels, but were still up to the task. The descent took about 35-40 minutes, with the video sped up to twice the actual speed (about 18 minutes). Their times would place time in the top 10% on Strava.


The video shows that the road was fairly smooth and wide. It's wide enough for cars to easily pass and vice versa. There are fairly long straight sections between switchbacks. Since the video clearly shows the brake levers, it easy to see that the rider used the straight sections to release (and cool) the brakes, and brake before entering the turn. He used the front AND rear brakes, and used the REAR brake by itself or as a drag brake.

During the descent, the Mike or the cameraman was able pass slow cars on 6 occasions (at 1:58, 2:52, 6:25, 8:03, 10:10, and 17:05 mark). There was no indication that the rider was slowed down by any cars.

The video clearly shows that cars and altitude didn't prevent these riders from descending Pikes Peak with caliper brakes and carbon wheels. A disk brake (s) would make the descent even easier.

As for Mt Ventoux, there has been a thread on this forum discussing the Ice-Tech "failures". Two or more tandems had over-heated Ice-Tech rotors that warped during the descent. Regrettably, they followed the Santana's ride leader's suggestions to use the rear disc as a drag brake to "save" the front brake. The warped rotor didn't cause an accident or injury. Once they let the rotor cool, these teams were able to complete the descent. At the end of the ride, they installed new Ice-Tech rotors and did the rest of the tour without further incidents. But they reverted to proper brake modulation (both brakes on and off) and the brakes worked fine. So yes, proper technique is crucial, just like with cars or motorcycles.

Do you still think that it's a good idea to only use the rear brake 90% of the time?

akexpress 

I'm going to reenter the discussion as I think we are being referenced here numerous times. We climbed and descended Mt Venteux with about 15 other tandems on a Santana tour a number of years ago. Every tandem had brake issues on the descent except the two that had drum drag brakes. We and our travel friends had avid BB7 rear discs and caliper front on our Calfee's and both melted the adjuster plastics off the BB7 caliper. Our friends are from Breckenridge Colorado and are crazy fast descenders but are a light team (280) and very experienced We are heavier at about 340 and lots of miles also. We did not descent with our normal technique but followed Bill McCready's recommendation to use one brake until it fails and then use the other brake to stop and let things cool. Never again will I use this technique. His reasoning is the most brake failures on cars, truck, motorcycles is the process of off-gassing which actually prevents the pads and rotors from contacting and will work again after cooling. However the bike brakes, one don't have enough power to actually allow this to happen and, two parts melt. BTW no one had hydraulic brakes at this time on their tandems. One team with two captains had calipers front and rear and used four water bottles and sprayed the rims all the way down. The stoker was petrified. Fast forward a couple of years we rode TRP HYRd on the rear with a Ice tech rotor and on an unnamed European descent of 17% two teams including us melted the rotors with the aluminum melting out of the sandwich construction. I favored the rear brake but used both and not as a drag brake. Changed my rotor to a Hope V2 floating and completed the rest of the tour. I vowed at that time never to use those rotors but have since changed my mind. Colotandem also melted a rotor on Venteux on a different tour I believe ( another very light team). Fast forward a couple of years and we were early adopters of the Di2 hydraulic brakes on the rear of our tandem with the same Hope rotor and and had good results. We then had a frame issue that may have been a result of the power of these brakes and which lead to a frame redesign by Calfee to accommodate these brakes. We had a new frame built with a disc compatible fork and now have a discs on front and rear with Di2 hydraulic R785 brakes. This has been a game changer for us and have done lots of the long steep descents with much more confidence. We are now using the complete system including the calipers with ceramic pistons and finned pads and the ice tech rotors for heat management. Using good brake technique is at least half the equation. We just completed a self supported tour of Vermont that has some rather impressive descents as we went to many of the ski areas. Our Calfee Adventure tandem is equipped with the shimano hydraulic system and we were very heavy with all the gear (over 400). We had to stop one time to let brakes cool just to be safe but again confident in the system . Our indicator to stop is the brakes get very noisy and start to chatter so we stop. The rotors are a bit noisy for while until they completely cool then are quiet again. We have been thru all the brake systems but am now settled on hydraulic at this point. On our adventure tandem I have two bar systems depending on the terrain we are riding and the flat bar setup has Shimano Saint 4 piston ceramic calipers and they are very impressive and have even better heat management. One team's experience but lots of real world testing and your results may vary. We also have hydraulics on our full suspension mountain tandems with zero issues.

pdlpsher

mtseymour,

I have watched all three of Col Collective's videos on Mt. Evans and Pikes Peak before today. You have failed to mention several key things. Pikes Peak is on a toll road with specific opening and closing times. Col Collective received special permission to start the ascent before the road was even open to the general public. That's why on the ascent video all you see is Mike and the camera crew. If you are on a bike, say you started climbing right at the toll road opening time, by the time you make your descent you will have a ton of traffic by the time of your descent. When I did Pikes Peak this year I arrived early but I still had to wait 30min. at the toll gate. The descent video is misleading and not representative of the actual traffic condition on this climb. Due to the early start the ambient temperature at the start of Mike Cotty's ascent was near 0 degrees C.

I rewatched the Pikes Peak descent video and paid attention to the six passings that you have identified. All of those six passes were illegal passes, crossing the double yellow line. And at the crazy speed he was going he most likely exceeded the speed limit on the toll road. Simply said, the video is a poor example of what an average rider will encounter on this road.

You also dismissed Mt. Evans as being the 'easier' descent than Pikes Peak based on the % gradient. Unfortunately you are wrong. Being on a 'free' road and not a toll road, Mt. Evans is not maintained to the same level as Pikes Peak which is on a toll road. Mt. Evans is riddled with cracks and pot holes. Some pot holes are more than six inches deep. Once you get above the tree line the road condition worsens. Contrary to what believe Mt. Evans is a much more difficult descent than Pikes Peak. There's simply no comparison. Many cyclists who made the ascent to Mt. Evans actually have car rides arranged to take them down so they can totally avoid the descent. Apart from the pot holes, there are large cracks in the road that run perpendicular to the direction of the road. They act as 'speed bumps' such that you cannot go fast even if there's no traffic.

I have personally done Mt. Evans three times and Pikes Peak twice. I shared my real-life experiences on this forum. You decided to turn to the internet and post videos to prove that my descriptions are experiences are false. This will probably be the start of a trend for as long as I'm on this forum. That's fine with me.

oldacura

I tend to believe that the experiences of most here are valid. What is true for one team at one time isn't necessarily true for all. We climbed & descended Mount Evans once about 8 years ago on the 4th of July. I remember the climb was long & difficult. Our old bike has rim brakes. We also occasionally installed a drum brake. I don't recall if we had it installed for that ride (likely so). I also don't remember how much we used it. The switchbacks near the top are tight & frequent. However it was cool (40s?) and I don't recall being concerned about rim heating. As stated earlier, the road surface near the top was pretty bad. Once we got below timberline, the curves opened up and we could carry more speed (didn't need to brake as much).

I have been concerned on some descents about brake heating but I don't recall this being one of them. Other descents at lower elevation with steeper grades and tighter switchbacks on hot days come to mind. I have tried to be mindful of heated rims under certain circumstances but we have never experienced any symptoms of impending failure.

PromptCritical 

Reviving an old thread.

This was a very enlightening thread, and I was surprised about the overheating of disc rotors on tandems.

We just picked up a new (to us) 2007 Sovereign tandem with a rear disc brake, and I'm wondering what the best current technology is for a rear disc.
(Our all up weight w/gear is 425#)

TIA

FBinNY 

Since you went to the effort of finding the heating thread, I'll assume that's the point of your question.

The short answer is that there's no new technology that addresses this.

PromptCritical 

Any advice on the best 700c tires?

TobyGadd

This thread is kind of a disaster, with a mix of conflicting information, unsubstantiated BS, and lots of FUD, obscuring some solid recommendations. But disc brakes were great in 2017, and they're about the same today.

Having ridden an MTB tandem with Magura MT4 brakes, and a road tandem with Avid BB7 brakes, down some steep stuff in Colorado, including Pikes Peak on both bikes, and Mt. Blue Sky (formally known as Mt Evans) on the road tandem, I've learned that disc brakes are reliable and safe. That said, here are some thoughts:

1. Rotor size is important. Both of my tandems have ~200mm rotors. Even bigger might be better, but I would not go smaller based on experiences with my solo MTB.
2. Proper braking technique is crucial. This absolutely means using both brakes so that heat isn't concentrated in just one. Never drag the brakes, but rather slow down quickly before releasing them again to blow off heat (stab and release). It's actually amazing how quickly rotors cool down with exposure to fast-moving air (yes, I did test this). I've tried alternating front and rear brakes, but I'm not really sure that I've seen any benefits--although I also haven't seen any problems either. Either way, dragging is bad, and stabbing and releasing is good.
3. Descend as quickly as you can while still staying in control. Air resistance absorbs an amazing amount of energy, so take advantage of it. Sit up high and stick your elbows out for the most drag. Maybe even put on partially-unzipped jackets before big descents to increase drag. I think that idea of drogue chutes and the like are fun, but I suspect that they would be very dangerous with any crosswinds. My wife and I have joked about adding "webbing" under our arms to add drag.
4. Metallic pads are good, although in fairness I've never tried anything else. Always make sure that you have enough pad material remaining before heading out the door, since metal on metal is terrible.
5. If you have hydro brakes, ensure that they have been bled properly. The only time I've ever brake issues is when there was air in the lines. Also, DOT fluid can absorb moisture over time--which can create vapor in the lines, leading to failure--so fully purge the fluid while bleeding. I've seen MANY poorly-maintained solo mountain bikes with this problem, especially at higher elevations.
6. Keep your rotors clean! If you get oil or grease on them, use lots of brake cleaner--and probably replace the pads. Hell, even braking on the flats with contaminated rotors can be terrible.
7. If in doubt, stop and let things cool down on difficult descents. I've done this a few times when stuck behind slow-moving cars on steep switchbacks when there's really no way to "stab and release" the brakes. If your brakes start chattering, or if you get stressed out, there's no harm in stopping for a bit for the heat to dissipate.
8. I've never tried dragging branches or anything behind me, but that sounds like a recipe for disaster. Ropes getting caught in the spokes/drivetrain? Catching on a guardrail? Bouncing and jerking from side to side? Yikes.

In short, disc brakes are awesome. Even my lowly BB7 brakes, which I figured that I'd have to replace with something more powerful like Paul Klampers, have never let me down. I've never melted or deformed anything on any descents. The only time I've had braking issues is when I haven't properly purged hydro lines or when I've gotten oil on the rotors. Perhaps new tech will be developed that allows people to descend 25% hills for miles while dragging only one greasy brake, but life is pretty good these days.

PromptCritical 

Thanks! It is an interesting thread as is the one about the descent of Mt. Ventoux in France. The failures surprised me.

How did you test the cooling of the disc (I'm a recovering engineer) brake? I've thought about making an air scoop to cool the disc.