Bicycle Mechanics - Control both brakes with one lever?

I just saw a picture of a bike with one brake lever and apparently two disc brakes. I have seen bikes with two brake levers (cyclocross), but I have never seen two brakes controlled by one lever.

In the motorcycle world there are hydro lines that split to both calipers. Is there anything like this in the bike industry (for cables or hydro)?

Single levers for both brakes has always been a fairly common practice for the handicapped and for tandems with caliper brakes and a drum or disc. Dia Compe makes a special lever and cables, and there are splitters out there.

The problem with 2 cable brakes is that they can't be proportioned and need to be kept carefully adjusted so both work together. It's much more practical for hydraulics which can be proportioned (4 brakes, 1 pedal in cars) but I don't know of any dual cylinder levers or line splitters for bikes, though there might be, since it's not something I keep up on.

For cable systems I know of at least two solutions:
J-Tek http://jtekengineering.com/AeroBrake.htm has the Model-S DoubleControl Cable Splitter

Problem Solvers http://problemsolversbike.com/products/cable_doubler has the BR3341 Cable Doubler 1:2
Dunno about hydraulic systems

Magura HS 33 a hydraulic rim brake made in Germany offers the possibility of balancing ..
but doubling the size of the slave cylinders that one master cylinder has to fill would change things
reduce power some ..

Actually using one of the present single masters to run dual calipers would not result in less power. What would happen is that you get double the stopping force for the same lever effort. It's because both calipers see the same PSI of pressure but now there is double the piston area at the calipers to do the work. So with hydraulics it's a winning situation. The downside ends up being that the master has to push twice as much fluid with the original size piston. So it's going to be pretty tough to make it work so that the engagement point is out away from the grip. Also any sponginess from the flexing of the piston seals and lines will be doubled so the lever will likely feel a bit spongy. The proper solution would be to double the area of the master cylinder piston so that you keep the same stopping force at the lever and pump twice the fluid. That would retain MOST of the original lever feel and lever effort while spreading the stopping power and heat between two calipers and two rotors.

Rivendell Bikes http://www.rivbike.com/products/show/uno-handers/15-170 has dual brake levers with either same-time or one-before-the-other actuation for V-brakes. Or Google "double brake lever" for other choices

Here's a double master cylinder fro motorcycles which might be adaptable: http://www.disabledmotorcyclerider.com/KLever2Flyer.pdf

Some great information here. Thanks for all the responses! Here are the pictures that got me thinking about this question.

http://forums.mtbr.com/attachment.php?attachmentid=435366&d=1235582906
http://forums.mtbr.com/attachment.php?attachmentid=435368&d=1235582906
http://forums.mtbr.com/attachment.php?attachmentid=435369&d=1235582906

It doesn't appear to have any special apparatus involved here. It looks to me like a standard Shimano lever with only one hose to the rear brake. Perhaps these images are of a bike in progress. It just looks to me like there is no front brake hose (even though a front disc is present).

You messed up the picture links somehow. All I see are red X's in boxes.

You can't control both brakes with one lever effectively unless you have an electronic system to control rear wheel skid. It doesn't matter if it's mechanical or hydraulic, either the rear brake will not engage except under maximal braking, or the rear wheel will skid under moderate braking. The loss of control that occurs with skidding is far more dangerous than the minimal loss of braking due to using a front brake only.
The only safe way to rig brakes for a guy who can only use one hand is to use 2 levers on the same side. One lever works the front brakes and is used for most stopping. The front brake alone will stop a bike almost as fast as both brakes in most circumstances. The rear brake can be used occasionally when powerful braking is not needed, like for speed control on long downhills, but it's not really necessary.
Any other set up is a mistake done by people who don't understand physics.

em, p.e.

Single levers for both brakes has always been a fairly common practice for the handicapped and for tandems with caliper brakes and a drum or disc. Dia Compe makes a special lever and cables, and there are splitters out there.

The problem with 2 cable brakes is that they can't be proportioned and need to be kept carefully adjusted so both work together. It's much more practical for hydraulics which can be proportioned (4 brakes, 1 pedal in cars) but I don't know of any dual cylinder levers or line splitters for bikes, though there might be, since it's not something I keep up on.

I think this brake lever: http://www.terratrike.com/shop/accessories/dual-control-brake-lever/prod_25.html has a "balance bar" so that braking force is equalized between the two wheels. It may be the same lever Rivendell sells. It's designed for recumbent trikes where two wheels are side-by-side. I agree that it's difficult to proportion braking power front-to-rear on a bicycle.

http://www.terratrike.com/shop/images/uploads/Accessories/DualControlBrakeLever%281%29.jpg

Inline Travel gents are an adjustable cable pull devise , depending on setup.

Unless you have problems with one of your hands that prevents proper usage of the brakes I would advise against this option. A safe, controlled stop on a bicycle requires two things - the maximum practical application of both brakes and avoidance of rear wheel lockup. I do not think it's possible to achieve both of those objectives without being able to modulate the brakes separately.

The link below goes to Google books capture John Forester's Effective Cycling book. Chapter 23, Emergency Maneuvers, includes a section on Panic Stops that is an excellent discussion of braking.

http://books.google.com/books?id=0n2t7P1v2M8C&printsec=frontcover#v=onepage&q&f=false

As an aside, the entire book is an excellent reference for both beginners and more experienced cyclists. Forester is an engineer and cycling safety enthusiast, and one of the pioneers in viewing the bicycle as transportation. I had the privilege of taking his Effective Cycling course back over 30 years ago, and then taught the techniques and safety practices in a 4-H Youth Cycling program. Even though I had been a mechanic for a few years at that time he taught me a refinement of tire changing that I've used ever since, and the "Instant Turn" technique has gotten me out of a jam more than once.

I've used the Problem Solvers 1-2 unit to good success. Meaning, I got it installed and working properly. Trouble is, you need to apply more force at the lever for similar stopping power to dual levers. Installed as a solution for someone with one weak hand; not the best solution because the additional effort needed at the one lever was also too much for customer's strong hand to stop effectively.

Actually using one of the present single masters to run dual calipers would not result in less power. What would happen is that you get double the stopping force for the same lever effort. It's because both calipers see the same PSI of pressure but now there is double the piston area at the calipers to do the work. So with hydraulics it's a winning situation. The downside ends up being that the master has to push twice as much fluid with the original size piston. Yes, you end up with TWICE the lever-motion for the same amount of pad-movement. This is like using standard-levers to pull V-brakes.

However, if you adjust the cylinder sizes (bigger master) for the same amount of throw with twin brakes, you end up with the exact same amount of braking force for the same amount of lever-squeeze force as before. The 100% lever-force is split into two, and 50% of the force goes to the front and 50% of the force goes to the rear.