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Tandem Cycling A bicycle built for two. Want to find out more about this wonderful world of tandems? Check out this forum to talk with other tandem enthusiasts. Captains and stokers welcome!

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Old 10-20-09, 10:28 PM   #1
scouse
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Brake question...

Can anybody suggest a source/brand/model for hydraulic disc brakes? Tonight's research makes me think that the standard systems are too short for tandems but I am probably missing something.

HELP!!
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Old 10-20-09, 10:45 PM   #2
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TG, or others, may have other advice, but my understanding is that you do not want to consider a hydraulic disc brake on a tandem because the disc has the potential to get so hot that the fluid will boil. Boiling = no braking. Get an Avid mechanical disc brake. Consider changing out the Avid disc for a Hope disc. Do a search (on the Tandem link) for "Disc Brakes". That should supply you with all the info you need.
My Avid/Hope mechanical disc works perfectly under very harsh conditions.
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Old 10-21-09, 08:37 AM   #3
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Magura?
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Old 10-21-09, 10:45 AM   #4
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Can anybody suggest a source/brand/model for hydraulic disc brakes? Tonight's research makes me think that the standard systems are too short for tandems but I am probably missing something.
Road or off-road use?

For off-road, there are a couple tandem-rated hydraulic disc brakes offered by Magura & Hope that come with tandem-length hydraulic lines pre-installed and pre-bled.

For road use, hydraulics can be problematic and are not the recommended solution.

So, what are you looking to put them on and how do you plan to use your tandem, e.g., total team weight, flat or hilly terrain, loaded touring, etc...?
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Old 10-22-09, 07:28 PM   #5
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My tandem is a Cannondale Street but the question actually relates to my Surly Big Dummy which has almost the same wheel base.

The weight limit is 200 pounds so figure 400 pounds onboard weight (the cargo is often my 7 year old plus groceries etc).

Riding is street and trail. Unlikely I will do any loaded touring although we do live in Pittsburgh which is pretty hilly.

I am confused as to why Magura are rated for off road but not road. Can someone explain?

Thanks
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Old 10-22-09, 07:51 PM   #6
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I am confused as to why Magura are rated for off road but not road. Can someone explain?
Off-road: Lower coefficient of friction on soil vs. paved roads coupled with lower speeds = lower brake energy / lower heat / significantly reduced risk of overheating brake fluid / mineral oil.

If the fluid lines are installed properly and use heat tolerant tubing, an open or closed hydraulic brake system will typically lock-up as heat migrates from the rotor and brake pads into the caliper's brake fluid chambers and causes the fluid to expand. Unfortunately, if you don't realize that you're overheating your brakes -- which doesn't take long on heavy bike coming down a steep grade with the brakes applied for prolonged period of time -- the lock-up becomes inevitable.

Now, that said, there are a few teams that have taken on epic tours with some heavy-duty, downhill/tandem-rated open hydraulic brake systems that purportedly had no problems due to overheating, even when tackling the big descents. However, I attribute that more to good cycling skills, good judgement and attentiveness to brake management.

So, there are some good, heat-tolerant hydraulic brake systems out there that are suitable for tandems. But the onus is on the consumer to understand that there are some potential limits to just how much abuse they can take -- which is true of rim brakes, drum brake and mechanical disc brakes -- and being attentive to the signs that your brake system is reaching that threshold so that you can still stop to let the brake system cool-off before a bigger problem develops.

This brings us back to the mechanical systems, like the Avid BB7. In addition to be a fraction of the cost of a good hydraulic disc brake, mechanical discs have a somewhat different failure mode when pushed to the point of overheating. While some of the plastic adjustment nobs can become deformed or melt right off the brake caliper under severe braking, out-gassing and brake fade (the same thing that limits most brakes) is the early warning sign for brake lock-up. So long as you haven't figure out how to fail both your front & rear brake at the same time, outgassing & brake fade are clear signs that you need to stop and let the brake system cool.

Last edited by TandemGeek; 10-22-09 at 08:19 PM.
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Old 10-22-09, 08:06 PM   #7
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Good advice and interesting to boot.

I am thinking maybe mechanicals would be best. Maybe BB7 with 180s?

Daily riding throughout the Pittsburgh winter is hard on wheel rims!!!
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Old 10-22-09, 08:14 PM   #8
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I am thinking maybe mechanicals would be best. Maybe BB7 with 180s?
If you're running MTB brake levers, then yes... the BB7 MTB caliper would be what you're looking for if the bike in question is the Big Dummy. When bought as a kit they typically come with a 185mm rotor and that's about right for the weight you intended to list, i.e., 40lbs of precious cargo + 160 lb rider weight for 200 lb total load limit.

For tandems, the 203mm rotor is more appropriate and requires a different caliper mount and the 203mm rotor. So, if you ever get a hankering to upgrade your Street Tandem to the MT configuration the larger rotors would be the better choice.

And... yes. Another benefit of discs is reduced wear on rims for folks who live and ride in wet or wet and cold places, not to mention better brake performance in the wet. Modulation on the mechanicals isn't as precise as hydraulics or even good road bike caliper or conventional cantilever brakes, but on par with most V-brake installations.
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Old 10-24-09, 03:31 AM   #9
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Going back a few years on the Hydraulic Disk systems. There used to be two types- an open and a closed system. The closed system was a completely sealed system and this is the type that under prolongued heavy braking- the fluid would expand and as it was a closed system- COULD apply the pads to the disc. This was cured with the OPEN system where any expansion of the fluid would return to the master cyclinder and NOT apply the brakes.

I have the Hope Mono M4 system On my Dale MT 2000 and bought it from my LBS. The standard piping was exchanged for a more durable type as it also had to be longer. As this was "Early" days for Hope to fit their brakes on Tandems- I did get a full guaranty that it would work but it was suck and see time. Disc size and we went for 203mm on front and rear. In hindsight- I would go for a smaller disc on the rear now as it is too easy to lock the rear under severe braking.

And as to effectiveness of the system- We can lift the rear wheel under severe braking and on a dry road we have yet to lock the front wheel unintensionally. That is why I suggest a smaller disc for the rear as that is very easy to lock up.

And if using an effective disc brake system on a Tandem- I would suggest a bolt through system for the front wheel. Never had a problem with the QR- but I do not fancy taking a chance on the front wheel pulling out.
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Old 10-24-09, 06:47 AM   #10
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This was cured with the OPEN system where any expansion of the fluid would return to the master cyclinder and NOT apply the brakes.
No, it didn't cure the problem... at least for tandems. It simply make it far less likely to happen.

Even an open system could be over-heated to the point where the fluid expanded beyond the capacity of the master cylinder under a variety of different scenarios:

1. The system had too much fluid to begin with (very common)
2. The DOT brake fluid was old and lost it's heat resistance (also common)
3. Plain and simple over-use of the brakes (easy to do on asphalt)

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And if using an effective disc brake system on a Tandem- I would suggest a bolt through system for the front wheel. Never had a problem with the QR- but I do not fancy taking a chance on the front wheel pulling out.
A bit off topic, but yes... if you (a) use a fork that wasn't originally designed for use with a front disc brake, or (b) that is poorly designed, or (c) that has been modified to remove any lawyer lips or other skewer retention features, or (d) uses silly lightweight skewers, or (e) put a massive rotor & downhill disc caliper on a fork that was not designed for use with a massive rotor, or (f) never bother to check or even know how tightly a QR skewer should be tensioned then you could find yourself at risk of a front wheel ejection.

No offense, while I understand what happened in the various documented front wheel ejections, it wasn't exactly an epidemic within the tandem community. Moreover, for as long as Cannondale has been selling it's dual-disc equipped tandems and as many of them as there are on the road I've never heard of a single front wheel ejection. Outside of Cannondale, I have heard of one or two front disc / road tandem wheel ejections but as already noted, they were custom one-off bikes that used forks never intended for use with a disc that had disc tabs added on and no lawyer lips or other similar features. Moreover, the wheels pulled out at very low speeds which also suggests the skewers weren't all that tight either.

Now, that said, for an OFF-ROAD TANDEM, a solid front axle is almost essential if you want to have full control over your steering. There's just too much torque steer on suspension forks when you're driving the front wheel through ruts and the like... regardless of what type of brake system you're using.

Last edited by TandemGeek; 10-24-09 at 07:00 AM.
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Old 10-24-09, 09:05 AM   #11
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No, it didn't cure the problem... at least for tandems. It simply make it far less likely to happen.

Even an open system could be over-heated to the point where the fluid expanded beyond the capacity of the master cylinder under a variety of different scenarios:

1. The system had too much fluid to begin with (very common)
2. The DOT brake fluid was old and lost it's heat resistance (also common)
3. Plain and simple over-use of the brakes (easy to do on asphalt)


No.1--that would be down to operator error and cannot be put down to the system- and on the open systems that is what it is- an open system that will allow for expansion of the fluid- or wearing of the pads.

N0.2-- Maintenance scedules from manufacturers suggest changing Fluid after "X" miles or at least yearly. On the Quality of the Fluid- There are various grades and the "Old" 3 or 4 may have this problem- DOT 5.1 is newer and does not have this problem with heat.

No.3--Never had a problem with overheating with over use- but that may also be down to the Large discs used that do dissipate heat well- but I have done a long downhill at dusk and could see the discs by the dull Orange glow they were emitting. By long I mean a 3,000ft descent at an average when descending of 12% and the brakes were in almost continual use but did get a rest on the few flat bits.

I used to make Brake systems for Karts (Go-Karts) And Some of the systems use a different type of Fluid. I never had any problems with either Fluid- except on 24 hour races where the DOT4 brake fluid attracted moisture at around 3 am in the morning. That did cause problems till I contacted Girling in the UK and aquired some special Brake fluid. This was DOT 5.1- although I did not realise it at the time.

But my feeling is -Why use Disc brakes on a road bike?- Unless it is for the additional drag brake and even then there are other options. Before getting discs on the T- we used V.Brakes and they were completely adequate for normal use. Only reason we changed was that on the long Enduros we were doing- after about 60 miles it was either the pilots hands or the brake blocks going off. Braking became very hard- which we do not have with disc's.
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Old 10-24-09, 10:52 AM   #12
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No.1--that would be down to operator error and cannot be put down to the system- .
Well, technically it's due to an error by whoever did the brake installation or maintenance and that is, after all, what causes most mechanical issues on tandems. In fact, that's what everyone who's ever had problems with any brake system that requires some technical knowledge to set-up and adjust has been told. Hydraulics just aren't no-brainers UNLESS you've worked with hydraulics... open, closed or otherwise.

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N0.2-- Maintenance scedules from manufacturers suggest changing Fluid after "X" miles or at least yearly. On the Quality of the Fluid- There are various grades and the "Old" 3 or 4 may have this problem- DOT 5.1 is newer and does not have this problem with heat. .
True, and hub manufacturers all issue maintenance schedules that tell owners to service their hubs on a regular basis, but that rarely gets done either. Now, to be fair, the DOT 4.0 systems that we first used in the late 90's have all switched over to mineral oil or DOT 5.1 in newer systems so it's not as much of a problem, if at all on properly set-up, maintained and utilized systems.

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-Why use Disc brakes on a road bike?
Exactly, which is why I'm still trying to figure out why you wanted to take the thread down a 'dirt road', so to speak with a protracted discussion on the different types of hydraulic brake systems and bolt-on front wheels which are clearly not road cycling / tandeming issues.
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Old 10-26-09, 07:56 PM   #13
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Thanks for the input and the ensuing interesting discussion. I ended up going with mechanical BB7s with 180mm rotors. LBS told me I will have to wait a while until the brakes "bed in" before I get the full stopping power but I can already feel a marked difference.
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Old 10-27-09, 05:24 AM   #14
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Did you or the local shop install them? Regardless, take a moment and visually see how many, if any, spacers were added to the caliper adapter and frame.

Avid supplies one pair of bolts for mounting the adapter. Most times these work well, however I have had installs that required a few mm's of shimming. These were possible to mount with the supplied length bolts, but when checked it was found the thread engagement was questionable.

Thick dropouts or spacing of the hub / frame / whatever can cause this.

The easy check is to see if the bolts end is near flush on the inboard end.

Just a thought to minimize a possible concern later.

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