akexpress 

PK I agree be careful and I have an IR temp gun and will try to get some temps on the brakes in a few weeks. I have enclosed some pictures of my avid that melted. It is hard to show but the inner adjusting pad is threaded into the body of the caliper. The post that is sticking out is attached to the red plastic adjusting ring which uses the dimpled ring on the the caliper to hold position as the inner pad is adjusted. If the plastic piece is gone there is nothing to stop the inner pad support from unscrewing it self out and falling completely out which in turn will let the inner pad fall out. This is what happened to our sister bikes brake the next day. On the second picture you can also see the discoloration of the body of the caliper itself due to the high heat it achieved.

PMK

I have two calipers here at home. One is a brand new spare BB7mtn. I also have a BB?road, the decal says BBDB / Avid / Road, came on our 2006 Co-Motion Roadster.

The designs are totally different. An obvious external difference is the BB7m has a Torx internal / hex external center on the adjuster, while the BBDB road has a blade to engage the plastic adjuster wheel.

The BB7m is as you described, yes if the plastic melts away, the entire pad adjuster is free to unwind and fall apart.

The road caliper, does NOT have threads cut through the body. The body is stepped, making a "stop" to prevent a total unwind of the adjuster.

After some research on the Avid parts breakdowns for later style road calipers. They are the same as a mountain except the internals are different for the different lever pulls.

Yes, this should have people take a lot of time to respect these brakes on long descents.

PK

Bostic

Here is a comment from one of the Volagi founders. All of their bikes have disc brakes.
https://www.bikerumor.com/2012/02/14/...#comment-88839

Thus far I have been very satisfied with the disc brake setup on our Cannondale RT2 riding around the usual areas of Silicon Valley. About the longest descents around here are HW9, 84 and eventually Mt. Diablo when we get stronger as a team. I have family in Reno and often climb both sides of Mt. Rose while visiting. The east side twists and turns upwards 16 miles from Reno to the summit while the west is a wide open 8 mile descent from the top to Incline Village. As a 285lb team I would hope that the disc brakes are much more effective than V brakes or calipers.

when

I think it would also be possible to drill a hole and thread it for a setscrew from the side that retains the pad adjuster bolt. With a small enough setscrew it is doubtful you would compromise the structural integrity of the caliper at all.

PMK

There are no doubt many ways to prevent the adjuster from falling out.

The real task is one to improve the detent system from plastic to something more heat resistant. If the pad adjuster were to unwind even 1/2 turn, this is a big change in lever travel. Several turns could render the brake useless, with the disc now rubbing the caliper housing when the brake is applied.

I have not disassembled the actuator mechanism, while it does use a plastic knob, the detents are supplemented via a spring clip. The plastic knob is still important though.

PK

Team Fab

Just my 2 cents.

Light weight rotors can fail as well. They can split along the spiders when they overheat.

Learned this one after a 5000 ft decent while riding La Ruta.

Chris_W

Part 2 of this series of Bikerumor posts is now up, and contains responses from 6 top wheel manufacturers, see here. Interestingly, several of the companies believe that disc brakes are not appropriate for road racing - their weight and aerodynamic costs being too great compared to the braking benefits. Not much info in this one that is really related to tandems, but a good read anyway.

StanleyJ

So here I am in Hong Kong, land of not particularly tall mountains, but the descents are steep (occasionally 20~25% grade) and twisty. Average grade down 2000ft could average 12%... so I was quite chuffed (because I'm looking at a tandem purchase) that the British guys at Hope made the remote master cylinder V-Twin which drives the XC MTB X2 caliper:

https://www.hopetech.com/page.aspx?itemID=SPG343

So that'll work nicely with the brifters normally seen with road bikes. However, as the remote master cylinder appears to be based off "Race" series brake (rather than the "Tech"), that also infers that the V-Twin has a disc limit of 160mm. However, it also means the V-Twin should be able to drive the M4 "all mountain" calipers, which Hope confirmed in an email it would work and that "some point in the future", they'll offer this as a standard options.

This would then allow Hope's 183mm & 203mm rotors (fixed and floating) to be used, which I would think should be more than enough, considering Clyde-size 18 stone MTBers can drag Hope M4's with just 183mm rotors and have fade-free braking. Hope also can make custom sized rotors. I would hazard a guess they can go to the 255mm size which apparently Santana now offer as the only option as the rear disc brake rotor size?

Ritterview

The demand for rotors larger than 203 mm appears to be limited to tandems, and the numbers are there so small as to not command any rotor maker's respect. Santana has a proprietary deal with a company so to make the 255 mm rotor. Formula's 220 mm rotor is discontinued, but it is a nice size. i had to have the chainstay modified to make it fit.

CaptainHaddock

Hi PMK! I've kind of followed you over from the MTBR forums (same Captain Haddock here). I wanted to ask since you've taken the time to pull them apart, does it appear that one could swap the internals from a mountain BB7 into a road BB7?

Chris_W

AFAIK, the internals of the mountain and road Avid BB7 brakes are the same. It is only the actuation ratio of cable pull to pad movement that differs between them, so that they are compatible with different types of brake levers.

Interestingly, Shimano announced some new cable disc brakes last week designed for road and cyclocross use that should be available some time this summer. They do not appear to have any plastic parts, but it is not clear whether the pads are as big as on the BB7 or whether they are rated for use with large tandem-sized rotors and heat levels, but they might make an interesting alternative. The new Shimano brakes are claimed to have a lot lower profile than the old Shimano versions, and that is one problem that I have with the BB7's - they often get in the way of racks and fender stays; however, it is not clear how the new Shimano models will compare to the BB7 in this regard.

TandemGeek

FWIW: Mark Johnson from Precision Tandems just sent me a Bengal MB700T, a Bengal 203mm rear rotor adapter & a Bengal-provided 203mm rotor to test out on our Calfee. I will be updating my blog with a preliminary report and subsequent updates as we put some miles on the alternative disc caliper and the Bengal-provided 203mm rotor.

However, at first blush the Bengal appears to be a direct replacement for the Avid. Mind you, this is a dead-stock Bengal MB700T that Mark is sourcing from Bengal. The only difference I can see or detect between the one that was on the Santana Beyond we rode at Santana's Chattanooga Rally is the color (this one is black) and the lack of the word "Tandem" on the caliper body. I should have checked, but I believe the Bengal-spec'd rotor is a bit more robust than the Avid rotor we've been using.

Installation was exactly the same as the Avid. Bolt the calper to the adapter with two machine screws, then bolt the adapter to the frame's I.S. disc mount on the back of the rear drop-out. While the Bengal lacks Avid's Tri-Align™ Caliper Positioning System™, so long as your I.S. disc caliper mount is properly aligned with your frame the Bengal is also a no-brainer to set-up. The inboard adjuster is manipulated using a 5mm hex drive and has a small 1.5mm hex head-driven fixing screw that holds it in place once you have it adjusted. There's also a knurled cable stop / adjuster where the brake cable housing attaches to the caliper which is a bit more intiutive to use than the outboard adjuster knob on the Avid.

Performance out of the box is really quite excellent. No rotor rub or "chiming" (something we heard a lot of with the larger rotor on the Santana) and even without being seasoned, great stopping power with normal lever travel. I rode the brake a few times on our Sunday loop in an effort to bed-in the pads and season the rotor. Again, even without being fully broken-in we were able to lock the rear tire on the 8% grade going into our community using only the rear brake. Mind you, we're only about a 280lb team.

Again, no plastic parts are in evidence.

More details and photos will go on the blog as time permits.

In case anyone is curious, I believe Mark has an upcharge of $50 for the Bengal MB700T vs. an Avid BB7 in his various Disc Brake kits. It's hard to back into the actual cost of the Avid BB7 from a price sheet since Avid doesn't sell a BB7 with a 203mm rotor that you can bolt onto a tandem. You have to buy the stock BB7 Road, the mounting adapter and the 203mm rotor ala carte as well as a thread-on rotor adapter assuming you have a left-hand threaded rear hub. If you have a rear disc hub or already have the thread-on adapter, then you save a few bucks on the kit.

Carbonfiberboy 

There are problems with every system, for sure. A riding buddy had his front caliper cable come loose on a short steep bit. His rear disc quickly overheated and he could not stop the bike. He went off into the blackberries, no oncoming, very lucky. We've been able to descend steep windy bits even fully loaded with our rim brakes, but don't think we could handle steep windy long bits. If we're going into the unknown or the steep known, we put on the rear wheel with the drum.

TandemGeek

.... and if he had the same thing happen with a rear caliper brake instead of a disc the difference would have been??? Just saying.

WRT to the front caliper brake cable coming loose, IMHO torque wrenches are way undervalued. Followed closely by periodic cable replacement.

oldacura

Interesting reading. I had no idea that the considerations to adapt disc brakes to road bikes were so involved: fork design, seat stay strength, wheel dish, spoke lacing, spoke types, etc. Is this a solution looking for a problem? We have descended most of the mountain passes in Colorado (some several times), Mt. Evans (highest paved road in N. America) and Haleakala in Hawaii with rim brakes and never had a problem. It sounds like the margin of error for discs is much smaller. Will manufacturers' liabilty concerns make this technology too expensive for wide acceptance?

Question: If you take 2 otherwise identical bikes, one optimized for rim brakes and one optimized for discs, which will be lighter?

TandemGeek

Supplemental brakes are a belt and suspenders approach that is only "needed" for certain heavy-brake use descent situations, e.g., larger teams, teams travelling fully loaded or anyone else venturing into steep grades who wants to either control their speed all the way down the descent or has a concern about over-using their rim brakes to the point where rim heating could cause a tire failure.

However, as you point out, there are just as many examples of teams who have tackled demanding descents with only rim brakes with zero problems as there are teams who have even had brake capacity issues on even not-so-epic grades.

While drum brakes have been the defacto drag brake for teams that needed the belt & suspenders, discs have always offered the possibility of having a somewhat lighter weight, less clunky-looking alternative.
- Early discs did not hold up well when used like a drum brake, but did well-enough for many teams that didn't put big demands on those discs, e.g., Hope mechanicals of the mid-90's vintage.
- Hydraulic discs were never a good choice for road tandems, and even Santana's much touted Formula hybrid struggled with heat.
- The Avid BB7 was mediocre at best early on when only the MTB version was available, necessitating some type of cable-pull modifier like a Travel Agent or BPB. The BB7 Road model addressed cable pull and has proven to be pretty reliable for folks looking to have something "better" than a rim-only rear brake. However, as noted from the Santana tour feedback provided by akexpress, still has some operational limits under extreme use.
- Santana's WinZip solved a few issues, but wasn't as user-friendly as the Avid and has now been replaced by the Bengal MB700T which looks to be a better mousetrap.
- Rotor diameter and robustness has been an issue, noting the 160mm rotors that work OK on single bikes are overwhelmed by the weight of a tandem where even 180mm rotors are too small. 203mm has become the benchmark that Avid used to qualify it's BB7 rotors for use on tandems as "primary brakes", noting that they do not approve nor recommend their use as a supplemental / drag brake: that's well outside their design limits. Santana has been spec'ing 10" rotors for their tandems and they seem to work well for most, but not for all: very thin, but large diameter rotors are hard to keep perfectly true.

So, where are we today? To your point, a tandem with disc brakes will be heavier and more expensive than a tandem with rim brakes; however, it's still lighter than a tandem with rim brakes and an Arai drum brake. A tandem with dual brakes will easily have far more braking / heat capacity than a tandem with rim brakes and is also unfazed by the weather. A tandem with rim brakes up front and a disc in back provides folks with the belt & suspenders who really are probably quite fine with dual rim brakes.

Lots of choices for consumers is always a good thing, so long as there is good information to support an informed decision. The latter tends to be the weakness, along with varying degrees of rider skill that will always lead to poor decisions regarding tandem brakes as well as problems with those brakes.

oldacura

I haven't really been paying attention to the disc brake discussion w/regard to tandems. Is the accepted technology for tandems mechanical (cable) or hydraulic (or both)?

TandemGeek

Road = Mechanical with at least 203mm rotors
Off-Road = Hydraulic preferred by most for techincal single track / Freeriding but, but Mechanical are typically "good enough" and more than adequate for double-track, fire roads and the like. Again, 203mm rotors.

Carbonfiberboy 

Just sayin' that things can go wrong, and that even a BB7 couldn't lock the rear with that stoker or stop the bike, and that the disc failed from overheat very quickly since it has so little mass. I don't know if a rim brake could have stopped the bike or not. Not my Avids, for sure. I once blew a rear tube on that same bit when rim heat blew it right through the rim tape. It's a well-known spot around here where several cyclists have had notable crashes on their singles. I went to sturdier rim tape and have done that bit several times since. I think you and this forum have done a good job of pointing out that discs have incredible stopping power, but also have problems which might not be apparent to the new disc brake user. It's good to progressively test one's braking system.

PMK

Captain, yes they can be converted, but why? I have never done that and honestly, would suspect the parts would cost as much as the entire replacement caliper assembly.

PK

PMK

Without spiking a controversy, I want to send post a consideration for disc brakes. We have thousands of miles on Avid BB7 brakes on our three tandems. Regardless of whether on-road or off-road, the brakes are not 100% maintenance free.

The brakes stop very well for us, and yes I can see there can be some concerns of overheating them.

For me, I have found that wiping the disc with a rag dampened in Brakleen, Acetone or lacquer thinner, will remove any contaminants and allow effective simple high performing brakes. Obviously this also requires brake pads that are not saturated in spray on chain lube or fully contaminated by another means, plus not worn to the backing plates.

When the discs are "dirty" the braking distances extend, and the brakes lack feel.

Typically I decide to clean or not based on the ride. A big event on unknown terrain, they are cleaned, a local training ride by ourselves probably not.

FWIW, this is a simple 5 minute job.

It works for us, may not for you, but decided to place it up anyway.

PK

PMK

We run discs.

In regards to discs off-road, I am not sure of how they average for tandems that prefer hydraulic vs those with cables. Yes, many teams do ride hydraulics off-road. We have ridden the hydraulics off-road and found them good, we now run mechanicals on that Ventana. They stop fine also.

I prefer the Avids for the reason of keeping all the tandems the same and spares common. I have no problem with hanging on and squeezing the lever, possibly from growing up with drum brake MX racers. Others do complain the lever effort is more than they care for so in that instances, hydraulics are preferred.

PK

uspspro

Shimano is coming out with a couple new mechanical disc brake calipers for 2013. They look very nice.

I wonder if they will bolt to any existing 203mm adapters?

Chris_W

I'm sure that the new Shimano mechanical disc brakes will bolt onto adaptors to use 203 mm rotors with them, there is no reason why they should not. My main questions about these new brakes is whether they can handle the heat of a tandem and the braking torque of the bigger rotors. Shimano have stated that one model is more designed for road use, I believe they are calling it the CX55, and one is more for cyclocross use, I believe the CX75. Does this mean that the CX75 is the minimalist, lightweight version that cannot handle long periods of extended braking? Does it mean that the model designed for road use will actually be up to tandem road use, or will it also be under-specced? I'd like to know more about the differences between the two models, including the size of the pads each one uses, and what rotor sizes Shimano recommend using on each. Hopefully all will become clearer closer to the vague launch date of "summer".

Ritterview

Googling....lessee....

Edit: Also interesting information on RD and cassette: