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  1. #1
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    Cantilevers vs. V-brakes vs. Disc

    [carried from another thread but important enough for its own thread]
    Just purchased a 2004 RT1000 with disc brakes and learned the following from another forum member regarding braking systems.

    http://www.rodcycle.com/testspecs.html

    This is compelling article on the use of different braking systems and their recommendations toward cantilevers for road and tandems mostly because of the weight, distance and speeds traveled by tandems and road bikes.

    What are the other experiences from others with the following braking systems on tandems.

    1. Cantilevers
    2. V-brakes
    3. Disc brakes
    dave

  2. #2
    Senior Member zonatandem's Avatar
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    Have riden with all 3 braking systems.
    Depending on team/tandem weight, where you ride or plan to ride (flat, hilly, mountains) and if you go self contained or not, and braking technique all can make a difference.
    Cantis: Have made 12 mile long descents, 7 pct grade with curving road with cantis. Anticipate your braking a bit (don't just jam the brakes as you hit the curve), alternate back and forth between front and rear brake (prevents possible over-heating but may cramp your fingers).
    V-brakes are definitely a bit more responsive than cantis if properly installed/applied.
    Discs: have ridden with double mechanical discs on fast descent (30+ mph) and they worked great, but consider them a bit overkill for our usage. Would avoid brake systems with fluids.
    Least maintenance problems were cantis and V-brakes.
    Longevity of canti brakepad record for us: 50,000 miles on a set of Scott/Matthauser pads on REAR of tandem.
    Needs (real or perceived), cost and type of usage all will come into play.
    If they stop you properly, what else do you need?

    Pedal on TWOgether!
    Rudy and Kay

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    What are the other experiences from others with the following braking systems on tandems.

    1. Cantilevers
    2. V-brakes
    3. Disc brakes
    I have the Cantilevers and they do take some adjustment expertise (maybe more like a lot of time) to get them adjusted - They're fine once adjusted right.

    Disks have the interesting effect that they require even the front wheel to be dished... after all the work to diminish or eliminate dish in the rear wheel (I have Ricthey OCR's on my road bike and love them), now we are dishing the front?!

  4. #4
    hors category TandemGeek's Avatar
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    Quote Originally Posted by NickK3
    Disks have the interesting effect that they require even the front wheel to be dished... after all the work to diminish or eliminate dish in the rear wheel (I have Ricthey OCR's on my road bike and love them), now we are dishing the front?!
    No worries...
    1. The forces acting on a rear wheel are several degrees of magnitude higher than a front wheel.
    2. The overall strength & durabilty of any wheel still comes down to matching the right design (i.e., number of spokes, type of spokes, lacing pattern, & flange height for a given team weight & intended use), with quality components and the skill / attention to detail of the wheel builder.
    3. As you note, Ritchey and Velocity sell off-center rims (OCR) that can be used on a front wheel to mitigate most of the front wheel dishing effect.

    If that's not enough, consider that those of us who have been slamming the wheels of our dual-disc equipped off-road tandems into rocks, ruts, trees and berms for many years now have been using 32h and 36h non-OCR rims without any major wheel durability issues. It might also be worth noting that the rear wheel spacing on some of the most popular "extreme" F/S off-road tandems feature 135mm rear spacing which, when combined with rear disc brakes, makes for some really shallow bracing angles on the rear wheels. Again, most of us have never been stranded by spoke failures -- just imploded Hugi, Coda, and Shimano cassette hubs, torn-off rear deraillers, folded cassettes and otherwise busted drivetrains.

    Just some food for thought and, yes, the physics acting on 26" fat-tired bike off-road are very different than the ones acting on a 700c skinny-tired road bike. But, torque is torque and the sideloads off-road far exceed anything a road bike's wheels experience during normal riding.

    But, to help alleviate any major fears about the newer dual-disc machines, we have several friends -- two of them tandem builders -- who have been riding dual-disc equipped road tandems for the past two seasons. Team weights range from 340lbs to upwards of 380lbs and the riding terrain has included the mountains in France, Austria, Switzerland, Italy as well as mountains in Washington State, Colorado, and North Georgia. There have been a few teething pains that have been addressed with the addition of strong return springs to improve brake feedback and modulation control, but that's about it.
    Last edited by livngood; 08-04-04 at 10:37 PM.

  5. #5
    Banned. galen_52657's Avatar
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    1. Cantilevers = light, simple, reliable, proven
    2. V-brakes = light, reliable, proven
    3. Disc brakes = heavy, complicated, semi-proven

    Do you ever think that manufactures just change things for the sake of change? Does anybody remember 'biopace' chainrings????

  6. #6
    Senior Member Lost Coyote's Avatar
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    Steps up and dusts off soapbox, climbs up and clears throat;

    I have recently gone through the entire spectrum on our first tandem. Our Trek T-2000 came with Avid Cantis. “More brake than you should need” I seem to remember someone saying when I expressed my dissatisfaction overall braking performance of the bike. Yeah right, I ignored the comments and set about upgrading the brakes to something I felt comfortable with. I worked on eliminating the cable stretch and housing compression along with upgrading to Paul’s Components Motolite V-Brakes with Travel Agents. This was a vast improvement over the standard Cantis, but I knew I could do better.

    I started researching disk brakes, and found some interesting stuff going on in the tandem community. It seems like a lot of people have strong opinions on the subject. For some reason former failed attempts at trying to use hydraulic disks as drag brakes has tainted many away from disk brakes entirely. Also a lot of people seem to forget the simple physics behind the fact that the majority of your stopping power comes from your front brake, not your rear brake. IMHO those who are slapping on a rear disk brake aren’t properly addressing the problem, they are most likely taking advantage of existing tabs on stays, or of hubs built for drum brakes which adapters for disks can be mounted on. Of course the major drawback to a proper brake upgrade, is additional cost of a fork with disk brake tabs. The mountain biking community has fortunately helped out quite a bit as the mechanical disk brake systems (such as the Avid Ball Bearing) are now simple and reliable.

    The end result of my research is that we’re using a Winwood carbon fiber Cyclocross fork with an Avid BB Mechanical disk. Oh yeah, I’m still using the Paul’s V-brake in the rear, as I’ve got the confidence in my current braking system’s ability, I don’t feel like I need it, even with a combined team weight of a little over 300 lbs.

    Sake of change, or status quo?

    Steps down from soapbox, leaving 0.02 on top.
    Gravity kills.

  7. #7
    hors category TandemGeek's Avatar
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    Quote Originally Posted by galen_52657
    3. Disc brakes = heavy, complicated, semi-proven. Do you ever think that manufactures just change things for the sake of change? Does anybody remember 'biopace' chainrings????
    While there are technologies of the moment, tandem builders have been searching for better braking systems as long as there have been tandem builders.

    Weight: Discs continue to be something that while not practical for a personal road bike (primarily due to the weight penalty), are an attractive tecnnology for tandems that are used in steep mountain terrain as the weight penality is nearly a wash when you compare disc brake configurations to the current status quo of rim brakes + a rear drum drag brake.

    Complicated: Hydraulics, yes... they are not for the novice or mechanically challenged. However, Avid's BB disc is as easy to install, set-up and adjust as a cantilever and perhaps even easier than a linear-pull that requires a travel agent. The least complex of the brakes that can be used on a tandem remain the road brake caliper; however, they're hardly ideal for serious tourists.

    Semi-Proven: This is true and false. They are proven for use in off-road applications, and as previously mentioned, several teams we know have successfully completed several seasons of road tandem use with either rear-only or dual disc installations -- including use in the mountains of Europe. What is not known or objectively tested are the physical weight and accompanying heat limitations or long-term durability and reliability. Clearly, there are folks who own tandems that are 10 years old and still sporting the original rim brake pads. Conversely, some teams have burned through a set of rear disc brake pads in only 20,000ft of descents. So, all this tells us is there are trade-offs and that disc brakes aren't suited for everyone.

    Bottom Line: Only time will tell if discs are 'the' solution that tandem builders have been searching for to round out the various choices they can offer teams who have special braking needs that aren't met by rim brakes and the time-proven, but heavy (and unattractive to some) Arai drum brake.

    Note: Several teams have been using mechanical disc drag brakes on road tandems since the mid-90's (or, since '98 for us).
    Last edited by livngood; 08-04-04 at 06:25 PM.

  8. #8
    hors category TandemGeek's Avatar
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    Quote Originally Posted by Lost Coyote
    Also a lot of people seem to forget the simple physics behind the fact that the majority of your stopping power comes from your front brake, not your rear brake. IMHO those who are slapping on a rear disk brake aren’t properly addressing the problem, they are most likely taking advantage of existing tabs on stays, or of hubs built for drum brakes which adapters for disks can be mounted on.
    Actually, while there is some degree of truth to the ease with which discs could be adapted to the rear wheel of a tandem vs. front forks, the real driver was addressing rear tire blow-offs from overheated rear rims/tubes/tires. Yes, true stopping power does come from the front brake, but human nature being what it is, tandem captains tend to use overuse the rear brake to control downhill speeds and that is why almost all of the tire blow-offs that you see on tandems are at the rear tire. So, that is why the discs first appeared on the back of road tandems instead of the front.

    Moreover, as Galen noted, discs are not universally looked at as a proven product for use on road bikes or tandems. Off-road, their utility and value are unquestioned but the demands of road riding, and particularly the demands put on brakes by a tandem are valid reasons for proceeding cautiously with their use. Additionally, it truly does take someone who has gained experience using the disc to help guide decisions regarding which teams might benefit from them vs. those who would do better with more conventional brake configurations. The latter is still a very scary area as even some of the tandem specialty dealers dont' have a lot of experience with disc brake systems, never mind a LBS dealer who hardly knows how to spell (or sell) tandems.

    Bottom Line: Yes, from an engineering perspective, you would definitely want to put the disc on the front; unfortunately, technology acceptance and human behaviour dictated a different migration path. However, the logic does support the idea that dual-discs may have great promise for use on tandems... but only time will tell.
    Last edited by livngood; 08-04-04 at 06:27 PM.

  9. #9
    Year-round cyclist
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    Two other points to consider, Mark:

    I haven't looked at the weight of a complete installation, but the disc brake itself doesn't impose too much of a weight penalty. For instance, Avid v-brakes and cantis weigh 180-210 g, while the BearingDisk (cable activated) weight 367 g. Add the weight of braze-ons in the first case, or disc brake tabs in the second case and the difference is minimal, I think.

    The major weight penalty comes with:
    - different wheel construction; a disc hub weighs a bit more;
    - frame construction.

    The latter point -- and the latter point alone -- is the one that implies the greatest weight penalty. The rear end of the frame is already well triangulated and doesn't need to be reinforced for disc (or Arai) braking, whereas the fork needs to be reinforced. The fork of a mountain bike is already big enough to whitstand the braking efforts, but the fork of many touring and most road bikes is NOT strong enough for that. Designing a "disc compatible" fork changes the behaviour of the bike and adds quite a few hundread grams.
    Michel Gagnon
    Montréal (Québec, Canada)

  10. #10
    Senior Member Lost Coyote's Avatar
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    Quote Originally Posted by livngood
    ....but human nature being what it is...
    Well then, if you are going to bring in human nature, all bets are off!! ;-)


    Quote Originally Posted by livngood
    ...tandem captains tend to use overuse the rear brake to control downhill speeds and that is why almost all of the tire blow-offs that you see on tandems are at the rear tire. So, that is why the discs first appeared on the back of road tandems instead of the front.
    Interesting point, and well taken, the only tandem team I know who has lost a tire from heat had a front failure. But, as I've said before I am new to the tandem game and don't have the exposure to many tandem teams. I also tend to forget who might fit the profile of an “average” tandem captain


    Quote Originally Posted by livngood
    ...Moreover, as Galen noted, discs are not universally looked at as a proven product for use on road bikes or tandems.
    I guess that is the root of this thread. What are this particular “universe’s” experiences with Cantis, Vs, and Discs. I (perhaps naively) tend to think that being relatively new to the tandem universe I might have a bit less biased view than those who have been around a while. However, I can say that even with my short time as a tandem captain, I found that (for me) a front disc up-grade has been money well spent. Additionally, up-grading to Paul’s Motolites along with eliminating housing compression and cable stretch was also money well spent.


    Quote Originally Posted by livngood
    ...Off-road, their utility and value are unquestioned but the demands of road riding, and particularly the demands put on brakes by a tandem are valid reasons for proceeding cautiously with their use.
    It goes without saying that proper brake set up is always cause to be cautious, especially if it is someone else’s bike!


    Quote Originally Posted by livngood
    ...Additionally, it truly does take someone who has gained experience using the disc to help guide decisions regarding which teams might benefit from them vs. those who would do better with more conventional brake configurations. The latter is still a very scary area as even some of the tandem specialty dealers dont' have a lot of experience with disc brake systems, never mind a LBS dealer who hardly knows how to spell (or sell) tandems.
    Very true, some riders may not be sufficiently mechanically inclined to recognize when they are in over their heads. A LBS retrofitting an existing bike with a disc brake system for someone who brings a bike in for even simple tune ups is scary in of itself. Mark, I think you have done a great job of educating and guiding those of us who frequent this board.


    Quote Originally Posted by livngood
    …unfortunately, technology acceptance and human behaviour dictated a different migration path.
    I guess it was that part (visible to me) of the path taken, which caused me to climb up on a soapbox. Who would have thought that (what now appears to be) commonly practiced poor braking technique combined with a lack of engineering/design foresight would cause such a serpentine path!


    Quote Originally Posted by livngood
    … However, the logic does support the idea that dual-discs may have great promise for use on tandems... but only time will tell.
    One can only hope. I can safely say that when I get ready to build my next tandem, I will specify dual-disc. It just might be possible that the market will drive the technology.

    Thanks for the discussion!
    Gravity kills.

  11. #11
    hors category TandemGeek's Avatar
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    Quote Originally Posted by Michel Gagnon
    Two other points to consider... the disc brake itself doesn't impose too much of a weight penalty. For instance, Avid v-brakes and cantis weigh 180-210 g, while the BearingDisk (cable activated) weight 367 g. Add the weight of braze-ons in the first case, or disc brake tabs in the second case and the difference is minimal, I think.
    Yup, the weight is only an issue if you are comparing discs to rim brakes, e.g., ~180 g. / ea for rim brakes = 360 g. vs. 734 g. for a pair of Avid's + ~80 g. for the added weight of disc hubs = 814 g.

    But, the Avids are usually looked at as a way to eliminate the 906 g Arai drum brake and that's where the weight "benefit" comes in, e.g., 1,266 g. for rim brakes + Arai vs. 814 g. for Avids = 1lb of weight savings. Now, if you look at the hybrid set-up where you run a rim brake in front & Avid in the rear you're looking at almost 1.5lbs of weight savings.

    Of course, if you accept that disc brakes belong on tandems you can then begin to look towards the use of disc-specific rims that can be made lighter because the rim no longer needs to work as a brake rotor, so there are even some additional areas where disc brakes could further reduce weight on a tandem in a very meaningful place -- rototating mass.


    Quote Originally Posted by Michel Gagnon
    ...the fork of many touring and most road bikes is NOT strong enough for that. Designing a "disc compatible" fork changes the behaviour of the bike and adds quite a few hundread grams.
    Maybe and maybe not. There is a lot of weight variability in forks. For example, a standard 1 1/8" Co-Motion chromo fork weighs about 1,230 g., whereas the older 1 1/8" standard Santana fork weighs about 1,020 g. The custom 1 1/8" steel fork made for our Erickson weighs about 920 g. Erickson has the advantage of knowing how much his clients weigh, whereas the Santana & Co-Motion forks are made for worst case scenario and likely overbuilt. So, there is a lot of margin in those numbers, even for steel.

    Let's look at carbon forks. A True Temper Alpha Q X2 is the lightest at around 450 g. The Reynolds Ouzo Pro tandem is closer to 650 g. The Wound-Up fork sold by Co-Motion weighs in at a bit over 900 g. Again, different designs and material approaches can yield significantly different weights that may or may not be indicative of a strength or durability issue, unless there are weight limits attached to the products.

    Now, just how much additional braking force does a hub mounted disc exert on a wheel and is it really the energy going into the brake that stresses a fork the most or is it the tire? After all, does the brake stop the bike or does the brake stop the wheel from turning which really means the tire's contact patch with the road is the fulcrum for the greatest stopping energy? Frankly, I don't believe the fork's crown knows if a disc brake or rim brake is increasing friction under the front tire and, after all, that friction with the road is what is responsible for slowing and stopping the wheel's rotation.

    As for where the braking action occurs, you're now looking at the geometry, distance, and loads that are transmitted between the brake pad contact patch with the rim (which is just a really big disc rotor) or disc rotor. Frankly, the only place I see an increase in the need for fork strength is in the lower 1/4 of the leg, at and below the caliper mount where, in most cases, a fork is already pretty durable. Given that most of the fork's mass resides in the crown and steerer -- which is where the lion's share of fork and front wheel loads end up -- you could easily beef-up a fork's tips & lower legs -- making them nearly solid if you wanted -- without increasing the fork's overall weight by much more than 10%: chromo or carbon. Anyway, that's my armchair assessment.

    My Humble Opinions:

    Discs are a sexy-looking way to get an Arai drum brake and perhaps up to 1.5 lbs of it's net weight contribution off of a tandem and to simplify braking on steep descents (i.e., eliminates third control). However, discs aren't drag brakes... so if a team really needs or wants a drag brake, a rear disc isn't a good choice as it precludes the installation of an Arai drum brake.

    If a team doesn't need a drag brake, discs might still be attractive and their extra weight may be a non-issue if they routinely find themselves on wet roads, encounter a very steep descent every now and again where for that one day of the year an Arai brake would be a welcome addition, or if they just want better stopping power than is currently available from the various rim brake options.

    Discs probably require more maintenance that rim brakes and at present seem to go through brake pads at a much faster rate. However, mechanical disc brakes such as the Avid BB are as easy or in some cases easier to install, adjust, and service as some cantilever and linear-pull brakes. Moreover, if a tandem owner doesn't do their own brake maintenance to begin with, then it really doesn't matter which brakes are easier to install, adjust, or service. If they do do their own work, the Avid's are quickly mastered and they can be improved upon.

    Bottom Line: Discs aren't for everyone but, at the same time, they aren't necessarily a bad thing. They can't cause a tire blow-off, aren't likely to fail (at least the mechanical ones if properly serviced and maintained), and if one does fail, the failure mode isn't catastropic (again, we're talking Avid not hydraulic) -- and even a single Avid BB is better than the best single rim brake.
    Last edited by livngood; 08-05-04 at 08:16 PM.

  12. #12
    Senior Member zonatandem's Avatar
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    On the weight issue for forks using a disc, there is now a carbon fiber fork being used/modified that has tabs for a disc and is currently being used on a very few tandems. And possible there is, or soon will be, a production c/f fork for disc and tandem use.
    Progress marches on!
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    Rudy and Kay

  13. #13
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    [QUOTE=livngood]

    My Humble Opinions:

    [...] Discs are a sexy-looking way to get an Arai drum brake and perhaps up to 1.5 lbs of it's net weight contribution off of a tandem and to simplify braking on steep descents (i.e., eliminates third control). However, discs aren't drag brakes... so if a team really needs or wants a drag brake, a rear disc isn't a good choice as it precludes the installation of an Arai drum brake. [...]

    Exactly right. I wish I had read and understood that before I bought my new tandem. I've found that with a team weight of 360 lbs, applying the brakes while dropping 500 feet quickly generates enough heat to melt the plastic parts of the mechanical Avid disc brakes that come on the 2004 Cannondale RT1000.

  14. #14
    dangerous with tools halfbiked's Avatar
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    Quote Originally Posted by andypdx
    Exactly right. I wish I had read and understood that before I bought my new tandem. I've found that with a team weight of 360 lbs, applying the brakes while dropping 500 feet quickly generates enough heat to melt the plastic parts of the mechanical Avid disc brakes that come on the 2004 Cannondale RT1000.
    Andy. Sorry to hear they haven't worked out for you, however your post is very reassuring to ME. We selected a 2001 or thereabouts cantilever equipped 'dale vs. a disc equipped '04. We'll ride it for a while to see how it works for us, though depending on the rear hub, I may want to add a drum back there to put under the stoker's control. Then, if more performance is desired, consider upgrading the forks for a front disc.

    The (very) limited experience we had testing a disc-equipped 04 was that even the bike shop had a hard time adjusting the brakes properly. I'm still unsure whether two discs would be a good idea on an extended tour.

    Brian

  15. #15
    hors category TandemGeek's Avatar
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    Quote Originally Posted by andypdx
    I wish I had read and understood that before I bought my new tandem. I've found that with a team weight of 360 lbs, applying the brakes while dropping 500 feet quickly generates enough heat to melt the plastic parts of the mechanical Avid disc brakes that come on the 2004 Cannondale RT1000.

    I responded to the similar post on the RT1000 issues thread that addresses my thoughts on potential solutions: http://www.bikeforums.net/tandem-cycling/60052-cannondale-2004-rt-1000-issues.html#post594142


    Quote Originally Posted by halfbiked
    I'm still unsure whether two discs would be a good idea on an extended tour.
    I think it really depends on the riding style of each team, the terrain they expect to encounter and whether or not the team is supported or unsupported. Quite a few teams have been riding custom dual Avid disc equipped tandems in Europe for two seasons now but I believe they have all been fully-supported (i.e., no panniers or excess weight beyond trunk bags with cameras and rain gear) and most of the teams are fairly aggressive on descents. Put another way, they don't use brakes much unless there's a turn to be negotiated.

    For loaded touring or less aggressive teams who prefer to control their descent speed through constant braking, I think the front disc, rear rim and rear drum brake configuration is a pretty good one. It gives a rider three brake technologies that all have their various stengths but where any of an individual brake's weaknesses is covered by one of the other two brakes.

    Bottom Line: Disc brakes are still a new technology for road tandems that may or may not be suitable for all teams. Make sure you discuss your riding styles with your dealer before making the jump to discs and also get a clear understanding of what they or the manufacturer will be willing to do relative to warranty / making things right (and for how long) IF you discover that your team's riding style is not conducive to the disc brake technology.

  16. #16
    Time for a change. stapfam's Avatar
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    I know in general that most of you are talking Road bikes, and I have a mountain Tandem. This was initially fitted with "V" brakes and these are quite adequate for the majority of users. However, I found that on the longer excursions that I take, 50 to 100 miles, and totally off road, Brake fatigue was coming in. This was both on the pilots hands, and the extra pressure to get gritty blocks to work on muddy rims. 4 Months ago we changed to Hydraulic Discs, Front and rear and what a difference. We now use less brake altogether, (With "v"s a confidence test for them was always given before full application), Downhill speed is higher, braking period is shorter, and we have stopped wearing out rims.
    I can assure you that these Hydraulic beasties are far more efficient than the cable operated things I tried about 5 years ago on a solo. They were about as efficient as putting a stick in the spokes. They did not work unless you put on full pressure, and then they suddenly stopped the wheel. Not confidence inspiring at all. I would still have reservations about using any cable operated disc system, but if it is possible for any of you to try a hydraullic system, then you will find the near ultimate in Tandem braking that it is possible to get.
    Incidentally, the system I fitted was the new Hope Mono M4 with 200mm discs, and boy, do they work.

  17. #17
    hors category TandemGeek's Avatar
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    Quote Originally Posted by stapfam
    I know in general that most of you are talking Road bikes, and I have a mountain Tandem... 4 Months ago we changed to Hydraulic Discs, Front and rear and what a difference. .... if it is possible for any of you to try a hydraullic system, then you will find the near ultimate in Tandem braking that it is possible to get.
    I would strongly recommend against fitting hydraulic disc brakes to a road tandem. We are also off-road tandem enthusiasts and have been using hydraulic brake systems on our off-road rigs since March '00. Without question, they are awesome brakes: hydraulics eliminate cable friction and provide you with incredible modulation control and caliper clamping power.

    However -- and I know this seems counter intuitive to what happy off-road tandem teams would be led to believe given what they must deal with off-road -- the hydraulic brakes are not as heat tolerant as the Avids or even the Hayes mechanicals and have inherently hazardous failure modes when subject to overheating that don't plague the mechanicals.

    Relative to heat resistance, road tandems require a significantly higher degree of braking power and as a result generate significantly higher friction / heat loads than an off-road tandem will experience in off-road conditions. The primary drivers are the differences in speed, the length of the descents, and the way that the brakes are used when comparing road to off-road tandems. Off-road tandems are operated at slower speeds than road tandems and do not generally encounter descents that are as long (time & distance) as do road tandems. Yes, off-roaders will often times encounter very steep or long descents, but it's rare that they will negotiate these descents at speeds above 20 mph unless they are in a dowhhill race and, after all, you aren't using brakes all that much in a downhill race except before the entrance to turns. Instead, off-road tandems will tend to keep the downhill speeds low through out the descent and even though the brakes are used extensively, controlling the wheel velocity at those lower speeds does not produce as much heat as it would if the same team were controlling their descent at 25 - 30 mph. That's the big discriminator since that's how many road teams descend steep hills. This differece is occassionally discovered by off-road tandem teams with disc brakes when they do encounter a relatively long, smooth descent that allows them to reach those road-like 30+ mph speeds where the brakes then have to be used extensively producing what you would expect: hydraulic brake fluid boiling / expansion and either a locked-up brake or a pressure leak/system failure. Been there and done that... having the rear brake lock-up the rear wheel on at least three or four occassions at speeds ranging from 10 - 20mph (thankfully, without a hydraulic line, fitting, or the master cylinder fail).

    Back to those failure modes, to the best of my knowledge, the Avids will not fail catastropically. Yes, you can certainly "cook" one and melt-off the adjustment knobs as already related to us and you can overheat and warp the rotors, and end up with melted brake cable housing, but the failure modes do not result in either a locked / skidding wheel or the complete loss of brakes while in motion. The latter can and does happen with hydraulics when they are overheated, along with warping discs, etc... and it comes on without much warning and there is not much you can do once it happends to mitigate the failure mode.. Larger rotors, metal jacketed hydraulic lines, and Motul 600 brake fluid will go a long way towards increasing the heat tolerance of hydraulic brakes, but even still, there is an upper limit to their heat tolerance that road tandems can exceed IF the operator uses the brake for constant speed control.

    Bottom Line: Do not use hydraulic disc brakes on road tandems unless you'll never encounter a steep hill. They will eventually bite-you if you encounter a situation where constant brake application on a long or steep grade is required and team weight is not a mitigating factor. Lightweight teams can cook hydraulics too; it just takes a longer/steeper hill or higher speeds.
    Last edited by livngood; 08-28-04 at 02:09 PM.

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    Older Than Dirt
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    So what about running a disc branke, either mechanical or hydraulic, on the front wheel, a V-brake as the primary rear brake, and a drum drag brake? Thoughts or sexperience are appreciated.

    Doc

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    Mad Town Biker Murrays's Avatar
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    Quote Originally Posted by DocF
    Thoughts or sexperience are appreciated.

    Doc

    I always appreciate sexperiece too!



    -murray
    "I feel more now like I did than when I first got here"

  20. #20
    hors category TandemGeek's Avatar
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    Quote Originally Posted by DocF
    So what about running a disc brake, either mechanical or hydraulic, on the front wheel, a V-brake as the primary rear brake, and a drum drag brake? Thoughts or experience are appreciated.
    As noted in my 08-27-04 04:58 PM posting, above Cantilevers vs. V-brakes vs. Disc...

    "For loaded touring or less aggressive teams who prefer to control their descent speed through constant braking, I think the front disc, rear rim and rear drum brake configuration is a pretty good one. It gives a rider three brake technologies that all have their various stengths but where any of an individual brake's weaknesses is covered by one of the other two brakes."

    rear rim [brake] = calipers, cantilevers, and linear pull, aka, V-brakes. My preference for a bike with bosses on the seat stays would be a good set of cantilevers (Avid 7, Paul's Strange brakes, etc...) vs. the linear pull / V-brakes. Cantilevers eliminate the need for the travel agent and the net impact to rear brake performance isn't all that dramatic since at any real appreciable speed the rear brake is only effective as a device for slowing a tandem/bike, not actually stopping it. But, that's just me.

    As for a hydraulic front brake, fogetaboutit: see my 08-28-04, 10:22 AM posting above: Cantilevers vs. V-brakes vs. Disc

    IF you want to fiddle with the disc brake technology on a road tandem go with a mechanical like the Avid BB7. Just remember, what makes a disc attractive for a road tandem is eliminating the risk of a tire blow-off from overheating the rim via a rim brake. Secondarily, they also offer better wet-weather performance and, thirdly, are generally grippier than rim brakes relative to max-stopping power. The downsides are, higher cost, added weight, reduced pad life, and added complexity -- at least initially since not too many tandem-savvy dealers or mechanics are up-to-speed on how to optimize them for tandem use.

    As for the heat issues, if a team is melting off the red plastic adjusting knobs they probably need a drag brake since those types of temperatures are developed under the same type of braking conditions that can result in tire blow-offs.
    Last edited by livngood; 08-28-04 at 02:07 PM.

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    I guess I shouldn't try typing when my blood sugar is low.

    You know, I was just sitting around watching the IRL at Nazereth, PA and it occured to me that what is needed for tandem bicycles is a ventilated disc brake rotor. I doubt we will see such a product as the market is limited.

    Doc

  22. #22
    Senior Member Brian's Avatar
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    Ok, I'm late to this thread. We tried custom 203mm titanium rotors on our tandem, with Avid mechanicals. 220km of riding, and the pads were gone, and the front rotor was showing wear. Great heat dissipation, but poor wear. We swithched to Shimano XT 203mm rotors, and all is well now. Heat is not a problem, as we use the brakes sparingly, even at speeds up to 60km/h. If the plastic melts, it's because you're riding the brakes. So far as I know, Avid is the only manufacturer that rates their mechanicals for tandem use. That's my $.02.

  23. #23
    Time for a change. stapfam's Avatar
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    Quote Originally Posted by Expatriate
    Ok, I'm late to this thread. We tried custom 203mm titanium rotors on our tandem, with Avid mechanicals. 220km of riding, and the pads were gone, and the front rotor was showing wear. Great heat dissipation, but poor wear. We swithched to Shimano XT 203mm rotors, and all is well now. Heat is not a problem, as we use the brakes sparingly, even at speeds up to 60km/h. If the plastic melts, it's because you're riding the brakes. So far as I know, Avid is the only manufacturer that rates their mechanicals for tandem use. That's my $.02.

    There is a different use of the brakes if you use discs on a Tandem. You let the speed build up to the maximum, and then brake sharply, and then off. When the speed builds up again, then brake sharply again. They are not a brake for applying continually. You have to think about getting the maximum size disc available, generally around 200mm, and look at the choice of pads. We have now done about 1000miles on the sintered pads, and so far, pad wear is minimal.

    I may be an offroader, but with a difference. We ride the tandem aggressively off road, and top speed in excess of 45mph downhill is common. Braking is only done where necessary, but we have one technical trail that has a 500metre drop at a very steep angle, Speed is not possible here so we keep the speed down by alternating front and rear brake

    Edited As I initially put in 500 metre drop. Actual height drop is 200 metres, spread over 500 metres, (Just to save any confusion)
    Last edited by stapfam; 12-04-04 at 03:42 AM.

  24. #24
    Senior Member Brian's Avatar
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    I've been reading your posts - you ride like us. Our tandem takes some serious abuse as well. We've got a custom ATC Racing fork (5" travel) with the 20mm thru-axle. This gives me the confidence to push the bike hard through the rough stuff. When I spec'd the frame, I had them make the Ti rotors too. Looked cool, but as I stated, not the best material for brake rotors. An expensive lesson.

  25. #25
    hors category TandemGeek's Avatar
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    Quote Originally Posted by Expatriate
    So far as I know, Avid is the only manufacturer that rates their mechanicals for tandem use.
    True. But, remember that Avid's endorsement only applies to its BB disc calipers when used in conjuction with the 203mm rotors and only for use as primary front and/or rear brakes, not as a drag brake. You'll need to consult with an authorized Avid dealer to piece together the right brake set-up for your tandem to ensure you end up with 203mm rotors front & rear. Moreover, anyone using a stock Avid BB rear disc may want to consider adding non-compressable cable housing and a helper return spring to the rear caliper to improve brake lever response if you still find the rear brake's performance to be somewhat lacking.

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