Chris Timm
Hans Christoph Timm

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Tandem bikes are hard on brakes. If you intend to ride your tandem in hilly terrain, you may not get by with using just two rim brakes. Many tandemists have experienced tire blowouts when they overheated their rims on long descents. Santana Cycles has reported reaching rim temperatures of around 220°C (425° F) in tests. Using one or two non rim brakes alleviates this problem. A brake which doesn't heat up the rim cannot melt your tube. The standard solution to this problem was the addition of an Arai drum brake to a tandem's rear hub. The Arai is still the simplest and most dependable solution. It weighs a ton, though (more than two pounds, to be exact), and it leaves you with the problem of how to actuate three brakes with two hands. Also, it doesn't look cool. This is where disk brakes come in.

An important remark on safety and warranty issues: The brakes are possibly the most important component on your bike. Only a sudden fork failure (see here for pic of a Hanebrink tandem fork broken in use) could be as dangerous as a defectice brake! On this page, I describe some modifications riders have made to their brakes to improve performance. Do note that almost any modification not specifically recommended by the brake manufacturer will void your warranty! Magura is very strict in advising their customers not to use adapters or aftermarket rotors and pads. That doesn't mean that these modifications cannot be safe, but any change you make to your brake is out of the manufacturer's control. Thus, don't come back to them crying if your brake decided to quit working just as you wanted to avoid that big ole tree!! Count yourself lucky if you still CAN cry, and promise to wrench more carefully next time. Also: I didn't tell you to fiddle with your brake. I merely present some options highly skilled mechanics have. I assume no liability for any consequences! If your brake fails you must not be a skilled mechanic!

General Info:

1. What is the difference between a disk brake and a drum brake?
2. Why a disk brake at all?
3. Do disks stop better than other brakes?
4. Do disk brakes provide better modulation?
5. I heard that disks drag all the time. Is that true?
6. Can I use a disk as a drag brake?
7. I don't believe this stuff about how riding downhill slowly will stress your brakes more than going fast. Please explain.
8. I heard panniers can be a problem when used on a bike with disk brakes. How so?
9. New parts come with new problems. What can go wrong with disk brakes?
10. Why should I believe you?

11. What does 'mechanical', 'semi-hydraulic', and 'hydraulic' refer to?
12. Aren't hydraulic brakes hard to service?
13. What does 'floating caliper' or 'fixed caliper' mean?
14. Are more pistons better?
15. What does 'open' and 'closed system' refer to?
16. What are the differences between the various fluids used in hydraulic brakes?
17. Which disks will hold up to tandem duty?
18. Which brake can I use to back up my two rim brakes?
19. I can get an older model disk at a super discount. Should I go for it?
20. I want to use drop bars. Which lever choices do I have to actuate a disk brake?
21. I have an S&S take-apart tandem. Can I still use a hydraulic brake?

22. Which brake fluids are compatible?
23. My frame doesn't have disk mounts. Can I still use a disk brake?
24. My bike doesn't have a disk hub. Can I still use a disk brake?
25. I heard there are so many different mounting standards. Please help me out.
26. I heard mounting a disk to a tandem frame can be especially difficult. Why?
27. I can't get my caliper centered over the rotor. Any tips?
28. What do I have to keep in mind when lacing up a wheel for a disk brake?

29. I want to use a larger rotor. Is that possible?
30. Can I use a rotor from brand X with my brand Y caliper?
31. Can I activate my Magura disk brake with a rim brake lever?
32. Should I get braided tubing?
33. I want to get one of those fierce-looking disk covers to protect my rotor from mud and rain. What do you think?

34. I put a new disk brake on my bike, but it performs very poorly. What did I do wrong?
35. Anything I should know about bleeding a brake?
36. I keep overheating my brake. What's wrong with it?
37. I have brake 'X' - do you know any tricks on how to service my particular model?
• Magura
• Formula
• Santana / Formula
• Hope
• Hayes
38. I heard many good comments about Hope brakes, but I have a hard time getting a particular model or spare parts. Can you help?

A disk brake consists of a rotor (the 'disk'), which is mounted to the hub, and the brake caliper, which mounts to the frame. The brake pads in the caliper squeeze the disk, thus slowing the vehicle down. All high-performance cars and motorbikes use disk brakes. A rim brake is technically a disk brake, with the rim acting as the rotor.

A drum brake consists of a large drum, which hides all other parts of the brake. The brake pads are inside the drum, and when actuated, they press onto the inside of the drum shell to slow the vehicle down. Drum brakes can be integrated into the hub (available from Sram and SunRace Sturmey-Archer), or they can be screwed onto threads on the side of the hub (like the Arai drum commonly used on tandems). A coaster brake is a type of drum brake activated by pedaling backwards, though the term 'drum brake' usually only refers to models operated by hand.

Some modern drum brakes from Shimano and Sram look like like disk brakes because they have an additional disk-shaped part to dissipate heat, but they are still drum brakes.

Drum brakes usually do not provide enough stopping power to stop a tandem safely, and internal drums also cannot take nearly as much heat as would be required to let them be used safely on heavy vehicles.

• Disks look cool (face it: that is a very big factor for many people)
• You won't melt a tube if you use a disk instead of a rim brake.
• No need to worry about worn brake surfaces on your rims if you use a disk instead of a rim brake.
• You can keep on riding even if your wheel is too much out of true to pass through a rim brake because you broke a spoke.
• Replacing a broken spoke is easier than on wheels with an Arai drum (wheels built by a competent wheel builder do not break spokes, though!).
• The Arai drum brake can only supplement rim brakes, not replace them. Because they provide enough stopping power, some disks can be used instead of a rim brake. Thus, you only need two brake levers to stop your bike safely.
• Good hydraulic disks provide excellent modulation.
• Unlike rim brakes, which perform very poorly in wet weather and the snow, most disk brakes are almost as strong in adverse condition as when it is dry.
• Supporting bike parts manufacturers by buying ultra-expensive parts is always a good deed.
• See my separate page on which brake set-up is best for your personal needs.

You need to consider three factors when judging a brake's capabilities:

• Sheer braking force: The heavier your vehicle and the steeper your descent, the stronger your brake must be. However, if your current brakes can lock up the wheel under all circumstances (dry pavement), then your brakes are strong enough. Since the rim is the largest possible disk diameter, most disks are not stronger than good rim brakes: Even a cantilever brake, a type of brake considered 'outdated' by many people, is sufficient to lock up a tandem's front wheel if set up right. Some current disk brakes are considerably weaker than good rim brakes. Good disk brakes require less hand strength for the same brake force, though. E.g. Magura gives a possible deceleration of 7.9 m/s² with 100N squeezing at the lever for the Gustav M (their strongest disk), while listing only 4.2 m/s² for their strongest rim brake (the HS 33). Using a larger diameter rotor increases brake force, so for a tandem you should always choose the largest rotor possible with your disk brake.
• Modulation: Brakes are best if they offer you more choices than just 'on' or 'off'. Especially in technical terrain or when the road is slippery you need to be able to fine-tune your brakes very well. Good brakes release the pressure on the brake even if you only back off slightly at the lever. If you have brakes with poor modulation you need to release the lever completely to set a locked-up wheel free again. Generally, hydraulic brakes fare much better in this respect than cable-actuated brakes. Good hydraulic rim brakes (e.g. the Magura HS-33 for flat bars and the HS-66 for drop bars) feature great modulation. Cable actuated brakes can be almost as good to modulate if the cables are new, clean and well-lubed, but their performance will deteriorate rapidly with age. Good hydraulic disk brakes offer better modulation than the best rim brakes. Other disks, like the Magura Julie on my poor-weather single, are not easier to modulate than good rim brakes.
• Heat dissipation: The rim has a diameter larger than possible for any disk. Thus, it is not surprising that disk brakes have trouble taking as much heat as a rim brake. Disk brakes heat up much quicker than rim brakes. However, a hot disk does not pose the threat of torching the tube, thus high temperatures here are not as dangerous. Overheating a disk may result in complete failure of that brake, though, as the hydraulic fluid will boil and form gas bubbles or the disk may warp. As test results show, only the very best downhill disk brakes will take more heat than a rim brake, and none can take as much heat as the combination of two rim brakes plus an Arai drum brake! Thus, this combo still remains the only solution for heavily loaded touring and extra-long bikes (quads, quints, etc.). Using a larger diameter rotor increases heat dissipation, so for a tandem you should always choose the largest rotor possible with your disk brake.

Note that if you ride with panniers, you increase the heat your brakes need to endure twofold: The added weight is a factor, of course, but the panniers also interfere with the air flow needed to cool the brake. This is especially noticeable with a front disk in conjunction with 'lowrider' panniers. Stop more often to let your brakes cool off!

Brakes are best if they offer you more choices than just 'on' or 'off'. Especially in technical terrain or when the road is slippery you need to be able to fine-tune your brakes very well. Good brakes release the pressure on the pads even if you only back off slightly at the lever. If you have brakes with poor modulation you need to release the lever completely to set a locked-up wheel free again. Generally, hydraulic brakes fare much better in this respect than cable-actuated brakes. Good hydraulic rim brakes (e.g. the Magura HS-33 for flat bars and the HS-66 for drop bars) feature great modulation. Cable actuated brakes can be almost as good to modulate if the cables are new, clean and well-lubed, but their performance will deteriorate rapidly with age. Good hydraulic disk brakes offer slightly better modulation than the best rim brakes.

Some disks vary slightly in thickness, thus giving a sort of stutter effect. This greatly decreases your ability to modulate brake strength, and thus you should require your brake's manufacturer to give you a new rotor if you detect this problem.

No, like most general statements containing a phrase like "all the time" it is not true. However, disk brakes do drag - some more than others, but no disk brake is 100% drag free. Keep in mind, though, that disk drag does not waste a lot of energy: The radius of the disk is very small compared to the radius of the wheel, so a small amount of drag at the disk wastes less energy than a regular brake pad rubbing on the rim (due to the different pad compounds the disk will make more noise, though). And do not forget that no rim brake is 100% drag free either! On most bikes that pads rub the rim when you climb standing up as the wheel flexes. With carefull setup most disk brakes can be made to be virtually drag free. Even the Gustav M on my full-suspension tandem, a brake which was not even designed to be drag free, has no drag which is noticeable outside the workstand if set up correctly.

No! No disk brake should be used as a drag brake. It will overheat and fail eventually!

A drag brake is a brake which is switched on at the beginning of a descent to slow down the vehicle constantly. This method of braking keeps the maximum speed below a certain level, something which can be required to keep you or your stoker feel safe, or because the terrain does not permit higher speeds or because you are stuck behind a slow vehicle you cannot pass safely. Using a brake as a drag brake, also referred to as 'riding the brakes constantly', heats up a brake very rapidly. This will lead to failure with most brakes!

The same holds for a car's brakes: If you ride the brakes constantly down a long and steep mountain pass, your brake fluid will boil and your brakes will fail! Thus, it is advisable to let the vehicle roll in between turns and then brake short and hard before a turn. This will allow the air flow to cool off your brakes. With a car, you can also switch to a lower gear to use the engine to keep your speed in check. If you cannot and do not want to let your vehicle roll freely on the straight-aways you need to stop and let your brakes cool off.

The only bicycle brake which dissipates enough heat to be used safely as a drag brake on a loaded tandem is the Arai drum.

When you are using your brakes you are converting your kinetic energy into heat. This is not a problem if you are stopping your bike once, but when you are riding down a long, steep slope, you are constantly heating up your brakes. If you were to let your bike roll freely, a large part of the energy would be taken up by the wind resistance slowing you down. However, if you ride slowly, almost all your energy needs to be taken up by the brakes, thus heating them up very quickly.

If you ride VERY slowly, however, you are giving your brakes enough time to cool off. To do this you must ride considerably slower than even the most patient riders will be willing to do.

If you want to know more details look at the graphs on Dirk Bettge's site.

If you ride with panniers, you increase the heat your brakes need to endure twofold: The added weight is a factor, of course, but the panniers also interfere with the air flow needed to cool the brake. This is especially noticeable with a front disk in conjunction with 'lowrider' panniers. For this reason, some disk manufacturers like Magura advise against using disk brakes on travel bikes. Stop more often to let your brakes cool off!

You are right. Bicycle disk brakes are still rather new technology, but they have come a long way since the first models were introduced in the early 1990s. Mechanical and semi-hydraulic disks can of course give you the problems you have with any cable-operated part on bikes (which is why I prefer hydraulic brakes and Gore RideOn shift cables). Semi-hydraulic and hydraulic brakes can get leaky seals. This is one thing anybody is afraid of, which is why good companies like Magura offer a five-year warranty on their brakes! And you can bend the rotor, either in a crash or because someone riding behind you ran their front tire into your rear disk brake.

The most important thing to keep in mind is to keep the pads and the rotor clean. If you get oil or any other lubricant on either of those parts, you will most likely have to replace both.  You might be able to clean the rotor with disk brake cleaner (available at motor bike shops, gas stations etc.), but the pads are definately history. There is no need to shy away from dirt, though: Disk brakes are far better in adverse conditions than rim brakes.

If you want to keep your stoker happy, tell them to stay away from the rotor and caliper at all times! Burn marks on their calf from touching the disk may be cheaper than a tatoo, but is that really what they want?

Don't forget to think about what cannot go wrong: No more heat-induced blowouts, no more exploding rims because the sidewalls are worn, no more walking home because the rim is too wobbly to pass through the rim brake, etc.

You are absolutely right: There is a lot of balony floating around the internet. Mainly, I am just an ordinary cyclist with some technical interest who compiled some information he gathered from reading the three largest tandem email lists and various bike magazines. I ride and race single bikes and tandems on and off-road, and I have disk brakes on three of my own bikes. In addition, I occasionally race other people's bikes with other brands of disk brakes.

However, there is no reason why you shouldn't ask other people, read test reports in the mags, and form your own opinion. Brakes are possibly the most important part on your bike, and even bad disks aren't cheap, so think before you spend your money!

The three terms refer to how the power is transferred from the brake lever to the brake pads in the caliper:

• A mechanical brake uses a steel cable, just like most rim brakes. This means they are easier to service and lighter than hydraulic brakes, but this comes at the price of added friction. Also, the loooong rear cable on a tandem will stretch, reducing available brake strength. Mechanical disk brakes' biggest advantage used to be their low price, but since the advent of the Magura Julie hydraulic brake, which is sold for DM 199 (less than US$ 100) in Germany, that advantage is gone, too.
• A semi-hydraulic brake uses a regular brake lever, which pulls a cable, but uses brake fluid to move the pads. Thus, somewhere in between a cable-actuated master cylinder will be used. Depending on the placement of this master cylinder, the brake will perform more like a mechanical or like a hydraulic brake.

There are two reasons for using a semi-hydraulic brake: You may want to use a certain brake lever (like an integrated brake-/shift lever on a bike with drop bars), or you may be afraid of the dangers of a hydraulic brake (like ripping hydraulic lines in off-road use). The first will make placing the master cylinder as close to the lever a good idea (a system offered by Santana using a modified Formula brake, and by Hope), while the second argument will lead to a system which combines the master cylinder with the caliper in one unit.
• A hydraulic brake is an integrated system of a brake lever with integrated master cylinder, brake line, and caliper. As the components must be designed to be used together, you cannot choose a different lever. Good hydraulic brakes are more expensive than mechanical brakes, but they are also vastly superior in performance, and at least as far as one can tell after several years of use (Magura has been building hydraulic rim brakes since the mid-1980s), well-designed hydraulic parts can last very long. Well-designed hydraulic brakes require much less service than mechanical brakes (which is why I switched to a hydraulic brakes on my foul-weather MTB), and they are easy to service should they require it.

Hydraulic brakes require you and/or your dealer to learn new tricks to set them up right and maintain them. In principle, though, dealing with them is no harder than dealing with mechanical rim or drum brakes. Other than a change of pads once in a while, many hydraulic brakes require no service at all.

The biggest difference to mechanical brakes is that hydraulic brakes need to be bled if air bubbles got trapped in the system. To do this, you need a bleeding kit available from the brake manufacturer. Such a kit mainly consists of a syringe and various thread-in adapters needed to get the fluid into the system. If you read the instruction manual you should not have many problems doing this at home, though it is often advisable to have a second person around to lend you a hand. Magura supplies excellent instruction manuals with their brakes. For more see my bleeding tips below.

I own bikes equipped with hydraulic brakes from Magura and Formula, and I find the Magura brakes much easier to service. Over the years there have also been a number of posts on the mailing lists I frequent complaining about how finicky their Formula is to adjust. Since they are a small company, Hope Technologies is often slow when it comes to supplying parts, but once you've got them their brakes are easy to work on.

It is true, however, that most bike shops are still neither equipped nor trained to deal with the various hydraulic brakes. See below on specific tips on servicing your particular model, and contact your brake manufacturer for a list of certified service centers. Thus, if you travel far away from home, a cable-operated brake system might be a better choice for you.

A floating caliper is mounted in such a way that it can center itself in relation to the disk. Its caliper can also be built thinner, as there is only a fixed pad on the side facing the spokes. The disadvantage of such a system is that it will never be 100% drag free. The most prominent example is the Magura Gustav M. A fixed caliper cannot move in relation to the frame. Most bicycle disk brakes are fixed-caliper designs.

The number of pistons, or slave cylinders, in the caliper has no direct relation to the quality of a brake. If more, but smaller pistons are used, the total area of the brake pad touching the rotor may be greater. Some manufacturers also claim that a four-piston design will improve modulation, as one piston can be designed to touch the rotor earlier. More pistons on the other hand increase the complexity of the system and thus the amount of possible problems. Shimano XT and Hope DH and XC 04 (now called 'Enduro' for 2001) are four-piston brakes, while the Magura Gustav M is a floating-caliper two-piston design (meaning it has both pistons on one side, and a fixed pad on the side facing the spokes. Most others are fixed-caliper two-piston designs with one piston on either side. An exception are the Louise and the pre-2001 Clara from Magura, two super-light XC brakes, which are a fixed-caliper one-piston design. They bend the rotor slightly to press it against a fixed pad.

Unlike rim brakes, disk brakes get extremely hot! Rim brakes easily heat up the rim way beyond 100°C (182°F), but the brake itsself is insulated against the heat by tha fairly thick pad. Thus, the fluid in hydraulic rim brakes does not expand during the braking process. With disks, however, the caliper itself gets very hot, causing any type of brake fluid to expand. Closed brake systems leave no room for the fluid to expand to. Their lever will therefore gradually move away from the handlebar, the brake will start to drag even when released, until finally the brake will lock up completely.

Open systems have an expansion chamber at the lever. Therefore, the brake feel at the lever will theoretically be unchanged even when the brake is quite hot. I say 'theoretically' because as my experiences with the Formula on my off-road tandem show even open-system brakes can be overheated if the expasion chamber is too small, or because seals fail at high temperatures. Most modern hydraulic disk brakes are open systems.

Some closed system brakes (esp. Hope) have a dial at the lever for manual adjustment. This is basically a do-it-yourself expansion chamber. However, if you forget to readjust the brake after it has cooled down you may be left with no brake at all! Happened to me once in a race - right before tight turn - with an ugly wall at the outside -  S C A R Y !

Magura rim and disk brakes as well as the Shimano disks use mineral oil, while most other disk brakes use automotive brake fluid. The two are not compatible and must not be mixed or exchanged!

Brake fluid supposedly expands less when heated and boils at a higher temperature. Over time it draws water, though, which leads to a lowered boiling point. Therefore, brake fluid must be changed at least once every two years. Brake fluid comes in various mixtures, rated as DOT 2, DOT 3, DOT 4, DOT 5 and DOT 5.1. I have no information on what the numbers mean exactly, other that the mixture affects viscosity, heat expansion, boiling point, and compatibility. Some teams have reported that Motul Racing Brake Fluid 600, a DOT 4 fluid, is the most heat-resistant fluid available. Brake fluid must be handled very carefully, as it is poisonous, destroys most frame finishes upon contact, and irritates the skin.

The mineral oil used by Shimano and Magura does not deteriorate with age. This reduces the amount of waste; it is also less dangerous for the environment, the frame and your skin. As brakes using mineral oil instead of brake fluid can be just as strong and heat resistant as those using brake fluid if designed right, I would therefore consider them greatly preferable.

That depends: Do you want an ADDITIONAL brake to avoid toasting a tube on extra-long descents (then see below), or do you want to use a disk INSTEAD OF a rim brake? Any additional brake will increase your margin of safety if you add it to your existing brakes, but only very few brakes can be used as a tandem's only brake. Most disk brake manufacturers explicitly warn against using their disks on tandems: Shimano, Hayes, Coda, and other say 'NO' to tandems!

The only brake advertised as being strong enough for a tandem is the Magura Gustav M downhill brake. I have tested it in several long-distance MTB races (among them an eight-day stage race across the Alps with 75,000 ft of descending), and I would agree that it is absolutely up to the task.

The only other manufacturer which approves of their disks being used on tandems is Hope Technologies from England. They offer several models. Only their largest rotors make the brakes sufficiently strong enough for tandems, though. Especially the 4-piston Hope DH 04 (now called 'Enduro' for 2001) has received great reviews from off-road teams on the Double Forte-mailing list.

Santana market a modified version of the Formula HD-5 (now called 'Evoluzione') disk brake for their tandems. Due to its very large rotor (203 mm; Formula only sells rotors up to 185 mm diameter) it is reported to also be up to the task of stopping a tandem safely. See here for Santana's original posting to the Tandem@Hobbes-mailing list about this brake. (I have a 1999 Formula HD-5 with 185 mm rotor on my hardtail tandem, and it failed several times on extreme off-road descents despite changing to higher grade brake fluid, which is why I went with Magura Gustav M on my new full-suspension tandem).

Note that if you ride with panniers, you increase the heat your brakes need to endure twofold: The added weight is a factor, of course, but the panniers also interfere with the air flow needed to cool the brake. This is especially noticeable with a front disk in conjunction with 'lowrider' panniers. Stop more often to let your brakes cool off!

Tandems ridden in the mountains often need a third brake to keep the tires from overheating. If you are a light team and you do not want to put the heavy Arai drum on your bike, then a disk will be your only choice. (Even though some tandem builders do just that, adding a third rim brake would not help at all as it would still heat up the same rim and tire!)

Basically you are free to choose any disk brake you want since it needs not be strong enough to replace one of the rim brakes. Mechanical disks are cheap, and they might be a bit lighter, too. Many tandem teams have been using a mechanical brake from Hope Technologies, though that may not be made anymore (click here for Mark Livingood's description of the Hope on their Erickson road tandem). Most hydraulic rear disk brakes for singles come with enough tubing to be actuated from the stoker's bar. If you are not afraid of hydraulic brakes, my personal recommendation would be Magura's new Julie. It is dirt cheap, virtually maintanance-free, and tests in bike mags showed that it can take more heat than almost any other disk brake.

Remember, though, that no disk currently available is designed to be used as a drag brake (see above).

Hey, I don't work in the computer biz, so I'm all for saving money wherever you can. However, do keep in mind that bicycle disk brakes are still rather new, and all manufacturers' learning curves were rather steep the last years. I would think very carefully about saving a few bucks by getting an outdated brake. If you are looking for an affordable disk, my personal recommendation would be Magura's new Julie. It is dirt cheap, virtually maintanance-free, and tests in bike mags showed that it can take more heat than almost any other disk brake. I still would not recommend it as one of only two brakes on a tandem, however (see 'Which disks will hold up to tandem duty?' above).

Also keep in mind that there are still some brakes and hubs conforming to the old mounting standard floating around (see below).

Currently, no brake manufacturer makes a drop-bar lever for their disk brake, though Magura's marketing man Martin Schäfer has stated in an interview that they might come out with one in the not-too-distant future. Until that happens, you need to rely on a mechanical or semi-hydraulic design.

Most mechanical or semi-hydraulic brakes are designed for V-brake levers. Most drop-bar levers do not pull enough cable. The exception is the Dia-Compe 287-V, the only V-brake specific drop-bar lever. You can get by using the Sidetrack BPB (Brake Power Booster - also known as the Comtek C-Ted), which increases cable-pull. Any such device will also increase the inefficiency of a cable-actuated brake, though. See my separate page on on brake choices for bikes with drop bars for more.

The only exceptions are Santana's modified version of the Formula disk brake and Hope's 'Remote Reservoir', which use cable-actuated master cylinders. Both are compatible with any drop-bar brake lever including Shimano STI and Campagnolo Ergopower. The Hope version was said to be unavailable for a while, but my sources claim that Hope continue to make them. Personally, I have more trust in Hope brakes than in Formulas.

You are of course free to chose any brake and lever designed for straight bars if you are simply looking for a third brake to be activated by your stoker. Note that handlebar diameters on road bikes are different, but you should be able to get it to work with some modifications to the lever clamp.

Sure you can. Make sure that your frame comes with guides for the hydraulics line which allow for easy removal. You just need to remove the lever or the caliper from the frame and pack them with the rest of the brake system. Be careful not to kink your hydraulics line.

No DOT brake fluid must be used in brakes designed for mineral oil, and vice versa! Doing so not only voids the warranty, but it destroys the seals and will render the brake useless very quickly.

Mineral oil: Magura and Shimano.
Magura is now offering new thinner blue "royal blood" brake fluid. It can be used in all Magura brakes except the oldest rim brakes. The thinner fluid should avoid "lever packing" when the lever is repeatedly applied and released in quick succession.

DOT brake fluid: Most others (Hope, Formula, Hayes)

Also, not all DOT fluids are compatible: DOT 2, 3, 4, and 5.1 can be interchanged without problems, while DOT 5 fluid should not be exchanged or mixed with any of the others. DOT 5 is blue in color, while all others are the color of motor oil (gold/brown). I have exchanged the DOT 4 fluid in the Formula on my off-road tandem for DOT 5.1 fluid without problems. Still, since brakes are such a vital part you should always check back with your brake's manufacturer.

Some teams have reported that Motul Racing Brake Fluid 600, a DOT 4 fluid, is the most heat-resistant fluid available.

Santana's new manual for the Formula disk brake covers DOT fluids in greater depth.

Most disk brake manufacturers warn against using adapters when mounting their brakes. Sometimes, however, you simply have little choice. You could either have a framebuilder add disc mounts to your frame, which would make at least a partial repaint of the frame necessary, or you could buy or make an adapter. Several such adapters are available, and quite a few riders have built their own. I ride rear disk brakes on both my off-road tandem and my foul-weather single even though neither frame came from the factory with disk mounts. See my separate page on disk mount adapters for more info.

You need some way of attaching the rotor to the hub. The 'international standard', which by now has become pretty well accepted in the industry, calls for a six-bolt mounting pattern. In some cases you can get by without a disk-specific hub, though I see little reason to. If your rear hub has threads for a drum on the left side, then you could use the thread-on adapter from Santana or make your own (like I did on my off-road tandem). I have also seen an adapter which bolts onto the existing spoke holes in the left hub flange. Hubs are not overly expensive, though, so I would recommend that most people buy a disk-specific hub.

If you consider buying a new hub you should keep in mind that many freehubs will not hold up to tandem duty long. Gather plenty of information before you spend your hard-earned bucks on a hub that'll break on your first steep uphill!

True, there are several different and incompatible mounting standards, though the situation has been improving considerably. Most companies have adopted the new international standard (I.S. 2000) using two bolts to fix the caliper to the frame and six to bolt the rotor to the hub. The old international standard (I.S. 1999) looked just the same, but the distance between the frame and the disk mounts on the hub was larger. The frame and fork mounts remained unchanged, but the hubs and calipers changed: I.S. 1999 hubs work with I.S. 2000 calipers if spacers are used (though this fix is not recommended as it may increase brake squeal), but not vice versa. Magura has detailed drawings of both standards in the download section of their website. Some companies like Formula or Hope used to use their own mounting standards on the hub, but they recently seemed to have followed the larger companies, too.

Hayes brakes and Manitou forks still use an entirely different mounting pattern called 'Postmount', but adapters are available.

The Rock Shox Boxxer DH fork again uses a different mounting pattern. Magura offers a special Gustav M caliper to be used with this brake.

Note that if you change to a larger rotor you must either change to a different caliper or use an adapter to fix the caliper further away from the wheel's axle (see below). Each caliper is designed for a particular rotor, and they are usually not interchangeable. Also note that mounting standards for front and rear brakes are different, so you cannot use a caliper designed for use up front in the rear.

All of the following does not apply to tandems with 135 mm rear spacing, as that is the normal dropout spacing found on modern single mountain bikes, or front disks.

The international mounting standard defines how far the rotor mounting position on the hub is away from the caliper mounts on the frame (15,3 mm in the rear with I.S. 2000+; 16 mm with old I.S. 1999). The international standard calls for the inner surfaces of the dropout and the caliper mounts to be in one plain. Only a tiny amount of spacers should be needed, if at all; I had to use three 0.2 mm washers on my FS tandem. Sometimes it's even necessary to file the paint off of the caliper mounts. Most disk brake manufacturers now offer tools for this purpose. Any good MTB shop should be able to help you out.

Tandems have problems with this, as most use wider rear hubs than single bikes. I do not know if any tandem disk hubs comply to the international standard, or if they place the rotor further inboard (which would happen if they used a single-bike hubshell with a longer axle). To comply with the international standard, the hub manufacturer must use a different hubshell for each dropout spacing "standard" (135/140/145/160 mm). As this is not practical I would say it is the responsibility of the framebuilder to choose a specific caliper mounting position (probably further inboard than the dropout) and tell his customer which hubs work with his frame. Talk to your frame builder about the exact model of brake and hub you want to use and have them figure out the best way to put it all together.

If you have trouble getting your I.S. caliper (any make and model) centered over the rotor, check with your local Magura dealer: Magura supplies 0.2 mm (8/1000 inch) washers with their brakes.

Hub brakes put very high stress on the spokes. Therefore, you should not try to break the records for the least number of spokes (use 36 or more), the thinnest spokes (2.0/1.8/2.0 mm double butted spokes will be great; use 2.3/1.8/2.0 mm DT Alpine III spokes if you feel timid), or the lightest nipples (use regular brass nipples). Also, you should build the wheel very carefully, using high and even spoke tension (always a good idea, even with rim brakes). Radial spokes are an absolute no-no, of course; build the wheel triple-cross (or more if using 40 or more spokes) instead.

Magura recommends the follwing lacing patterns for disk-brake wheels: On the front wheel and the disk-side of the rear wheel, the spokes with inward-facing heads should point forward. On the drive-side of the rear wheel, they should point backwards.

You may find it hard to find disk-compatible hubs for more than 36 spokes. Don't worry - me and my friends have been using 36° wheels with disk brakes on off-road race tandems without problems. On the rear of my new off-road-tandem, I even use a 32-spoke hub with a disk brake (though the Rohloff Speedhub's symmetric flange spacing and large flange diameter help, too).

You probably already know that you need a different caliper or a mounting adapter, otherwise the larger rotor will not fit through your caliper. Some manufacturers offer several different rotor diameters, and they usually offer mounting adapters to change the caliper position.

E.g. Hope and Hayes both offer rotors up to 205 mm in diameter, and both offer adapters to fit their calipers. Magura do offer rotors in 160, 180 and 190 mm, all of which in theory can be used with any of their calipers, but they offer no adapters to fit their brakes. Magura believe that using adapters may be detrimental, and they will not warranty any changes made to their braking system which are beyond their control. A restrictive choice, but a wise one considering possible liability suits!

For 2002, Magura is now offering a new caliper holder for the rear Gustav M disk brake allowing the use of a 190mm rotor in the rear as well. This caliper holder can be retrofitted to earlier Gustav Ms. Rohloff also makes 190mm rotors to fit their SpeedHub.

Hope make a disk brake caliper adapter which allows the caliper to be moved radially out from the I.S. mount point in both 10 mm and 20 mm increments (20 mm and 40 mm diameter larger rotors needed). Other manufacturers (Hayes, Formula) make different adapters. Maybe you can find one with the right dimensions.

These caliper adapters will fit any I.S. caliper. Thus all you need is a rotor which fits your brake and is 20 or 40 mm larger than the one your caliper was designed for (e.g. use a rear Magura Gustav M (160 mm standard) with a Julie front disk (180 mm)). If you cannot find a rotor for your needs, Hope (and several other manufacturers) will make custom rotors for any make of brake. So in theory you could get a 185 mm brake setup, a 20mm adapter, and then a custom rotor of 225 mm, which is probably more than enough for most situations. (Thanks to Ian Yates for this tip.)

Do note that any of this will void your brakes warranty unless you use parts specifically designed for your particular brake (e.g. Hope brake and rotor with a Hope adapter).

Generally no, and doing so will void your brake's warranty! Each caliper is designed for a particular rotor, and they are usually not interchangeable. E.g., calipers differ as to how wide the brake pads are, so the braking surface on the new rotor you are trying to use may be too narrow.

However, I have read reports that noisy Hayes brakes can be quieted down by using a Magura rotor (if the diameter is the same - Magura rotors are available in 160mm, 180mm (Julie and 2002 Louise FR front) and 190mm (Gustav M)). If you decide to do this you are entirely on your own, though. I didn't tell you to do it - don't blame me if something goes wrong!

Magura disk brakes are an open system (i.e. with exapansion chamber at the lever), while all rim brakes are closed systems. Rim brakes do not heat up the brake fluid like disks do, so they do not need an expansion chamber. Also, both types of brakes use different diameter master cylinders, so the mechanical advantage of the levers will not match the slave cylinders. It simply will not work!

I have recently revised my opinion on this issue: Most people will not need braided tubing, but it does offer one advantage for the most hard-core teams: It can take slightly more heat. I will therefore switch my new tandem to braided tubing. This does come at a price, though: Literally, as they are usually very expensive, and also technically, as they can ruin your bike's paint job. Also, most braided hydraulics lines are supplied by aftermarket companies, something I would always be wary of. Yes, I run a braided 'Steelrod' hydraulics line on my off-road tandem, but only because it was the only one I could get in the required length. Magura buys the braided tubing they sell from Spiegler Bremstechnik in Freiburg, so buying from them directly should be considered 'safe'.

Hydraulics lines usually do not break. If they get caught somewhere and rip off, then failure will occur where the tubing is attached to the lever or the caliper, not in between.

Please do if you feel suicidal! Otherwise spend your money on something else instead. The disk covers keep the cooling air flow away from the brake, thus leading to failure from overheating VERY quickly.

Be patient. The new rotor and pads will take some time to break in. I put the Formula on my tandem the night before a long-distance race, and it took about 30 race miles for the system to perform well.

Bleeding most brakes is not hard to do, but if forget one important step, your brake might fail right in the steepest section of your most dangerous trail, so work carefully! You can access most manuals through the links provided below. IMPORTANT EXCEPTION: Bleeding Gustav Ms: There is some confusion as to what the correct bleeding procedure for bleeding the various model years of Gustav M brakes is. See my separate page for details.
To facilitate getting air out of the system you can use two tricks: Gently tap the brake system to release air bubble trapped somewhere in the brake, and bleed your system from the lowest to the highest point: The threads into which you mount the syringe should be at the lowest point, while the hole where excess oil leaves the brake should be the highest point. This will allow air trapped in the hydraulic lines to escape more easily. This may require you to mount the bike in a workstand and raise its rear end to let the caliper be higher than the lever.

Nothing most likely! Most likely you need to upgrade your braking technique, not your brake! Do not ride your brakes constantly; a disk brake must not be used as a drag brake! When riding with disk brakes, always let your bike roll freely as long as possible, sitting upright to use wind resistance to slow you down. When approaching a turn, brake hard to slow your bike down in minimal time. If you cannot or do not want to let your vehicle roll freely on the straight-aways you need to stop and let your brakes cool off.
If you feel confident that nothing is wrong with your riding style, here are a few changes you might consider:

• Should you have a disk cover or panniers on your bike: Take them off!
• Change to a better brake: I have had best luck with Magura Gustav M brakes.
• Try replacing your DOT brake fluid with Motul Racing Brake Fluid 600 (yes, this fluid is DOT 4-compatible). Several teams have reported that it is the most heat-resistant fluid available (do not do this if your brakes use mineral oil - see 'Which brake fluids are compatible?' above).
• Try going to a larger rotor. See above for more details on how to do this.
• Change to braided tubing.
• Try adding an oil cooler to your system. These coolers were originally designed by Centurion bikes to overcome problems they had with disks on their carbon-fiber rear swing arms. You can order them through your LBS under the parts number 17031602 from Centurion Germany.
• If nothing helps: Go back to using two rim brakes and an Arai drum brake.

Folks, I love working on bikes, and it seems like I end up helping all my friends with maintanance problems on their bikes, but I still only have hands-on experience with a very limited number of parts. All I can say is:

Magura:

• All Magura brakes I have worked on (Julie, Gustav M, HS-33) were very easy to handle once I read the manual. Magura's manuals and additional tech tips can be found in the download section of their website..
• For 2002, Magura is now offering a new caliper holder for the rear Gustav M disk brake allowing the use of a 190mm rotor in the rear as well. This caliper holder can be retrofitted to earlier Gustav Ms.
• Bleeding Gustav Ms: There is some confusion as to what the correct bleeding procedure for bleeding the various model years of Gustav M brakes is. See my separate page for details.

ATTENTION: Some early 2001 Gustav M leves had to be recalled. See here for more details.
• Magura's 2002 models should be bled using the new yellow transport spacer only.
• Magura is now offering new thinner blue "royal blood" brake fluid. It can be used in all Magura brakes except the oldest rim brakes. The thinner fluid should avoid "lever packing" when the lever is repeatedly applied and released in quick succession.
• If you have excessive brake drag on auto-adjust disk brakes (all models except older Louise and Clara), try the following: "I got in touch with Magura USA and was told to 're-animate' the caliper. That means to pump the levers with the pads removed but not to let the pistons pump out of the caliper. Sounds like a magic trick, right? That is said to re-lubricate the seals and possibly free a stuck piston." Thanks to Robert Kaechler for this tip! For the long version see here: English or German.
Formula:
• My Formula brake (1999 model, open system) came with a poorly translated manual, but I could usually still figure out what was meant by cross-checking the German text with the English and the Italian. The only real trick not found in the manual is that when bleeding the brake you should not screw the syringe all the way into the threads at the lever, but back it out about a quarter turn. Otherwise you will not be able to get any fluid from the syringe into the system.
• Formula have plenty of manuals on their website.
Santana / Formula:
• Check out Santana's new instructions on the Gear-To-Go website.
• A friendly Santana rider supplied the following tips for the brake:

1) Adjust the pad position as close to the rotor as possible without causing drag
2) Adjust the cable pull so the there is almost no play in the cable housing
3) Adjust the fluid level to be ½ inch below the O-ring.
Hope:
• Hope have posted manuals on their website.
Hayes:
• ATTENTION: None of the disk brakes offered by Hayes are approved for use on tandems.
• However, you can access manuals on their website.

I feel with you; the former Hope distributor in Germany, Raw Hope, was especially bad. They now have a new distributor, and let's hope that things will improve. If not, try Singletrack Bike, a British mail order shop that can get anything from Hope in a couple of days. They will ship it anywhere. (Thanks to Ian Yates for this tip.)