Technical FAQ: How to control two brakes with one hand
After last week’s column, there were lots of suggestions on how to control two hydraulic (or cable) brakes with a single lever. So, this week’s Technical FAQ column is devoted to these reader letters:
Just a quick suggestion for Efe looking to deal with braking with one hand. I have the same problem. I am left-handed, and I do all my shifting and braking using my left hand.
You can see from the picture that I have taken the right STI lever and placed it on the end of the left drop so that the brake lever is almost touching the left brake lever. This allows me to have independent braking, both front and back, allowing me to fully use each brake.
I also have Ultegra Di2, which allows me to modify what each lever does. In my case, both levers shift the rear derailleur, allowing shifting from both the drops and the hoods. To shift the front derailleur my mechanic stripped down a climbing shifter and we attached the stripped down shifter to the left STI lever just above the brake lever. The right side is just a dummy hood, which is completely stripped down.
This system has worked on this bike for 30,000km. The only thing I suggest (like you see in the picture) is to place a sandwich bag on the bottom lever to stop ingress of sweat from hands into the body of the lever. My lever failed after about 10,000km after which I started using the sandwich bag and haven’t had a problem since.
I too am a paracyclist and this setup seems to work for me. Hopefully this could help Efe’s friend.
In response to the question how to set up double brakes on a bicycle with drop bars, I have a couple different theories how to accomplish adequate braking using one hand.
Using mechanical brakes, use a brake splitter where one cable enters and two exit. Think of the old Odyssey Gyro setup used on BMX bikes. The trick will be figuring out where to mount it on a road bike. Of course this would not produce the front/rear bias that Efe was seeking, but it may be a relatively simple solution.
Assuming hydraulic disc brakes are preferred, a single lever set up would require, as you stated, a larger master cylinder to accommodate the increased fluid volume required to operate two calipers. If we pull from automotive tech, it is safe to say the right machine shop could make two separate master cylinders that could be connected together. One would be the rear master cylinder the other the front, each configured to provide the desired front rear braking bias. This is a common set up in racecars.
The next option for a hydraulic system would be to use proportioning valves installed after the master cylinder; this would give a fixed front/rear bias depending on what percent of fluid flows to the front vs. the rear once it leaves the master cylinder. Of course, this setup would also require custom machine work to create the master cylinder and proportioning valves.
In any case, finding the correct braking bias that would cover the most common situations would be the trickiest part of the equation. The center of mass on a bicycle is constantly changing based on rider position, so what works while seated wouldn’t necessarily work as well while standing. If it were me, I would lean toward the side of caution and shoot for a brake bias of F60/R40.
Your letter on December 5 about double brakes for a Paralympic cyclist lacked the most obvious answer.
The solution already exists in the automobile industry, where one pedal controls brakes on four or more wheels. The short story is that a balancing system/valve makes the front brake the primary brake and the rear brake function like a secondary brake. The automobile systems are of course more sophisticated and have “split points” to rebalance for harder braking situations. But that is because it is ten to thirty times the mass and 1,000 times more energy to decelerate a motor vehicle than a bike. A simpler lightweight system would be desirable and likely all the Paralympic cyclist needs for his bike.
Possibly all one needs for a simple double brake on a bicycle is the right ratio of large rotor in front and small rotor in back, such as 180/140 or 203/140.
Another simple system on a bicycle might also have a smaller hydraulic port for the rear hose, which will also reduce the force applied to the rear brake.
My reputable reference is a Society of Automotive Engineers PowerPoint they titled “Brake Systems 101.”
Maybe this is how the automobile industry can finally pay back cycling for its invention of the Bowden Cable.
Preferably, a professional engineer with computer-aided design equipment would incorporate calculations to get the ideal pressure balance needed for a bicycle over a broader range of weight/mass. Otherwise, you are in Graeme Obree-like experimental territory. But Campy claims that a single pivot in the rear brake is enough to provide both hands with the feeling that equal pressure is applied by both hands and provides superior braking control.
One possible solution to get two hydraulic brakes operated by one lever would be to use a cable-actuated lever and a cable-to-hydraulic converter. You could probably come up with a cable arrangement with a single cable in the lever that gets split to two cables at the actuator. You could adjust brake balance by using separate barrel adjusters to each side of the hydraulic converter. It would take a little fiddling to do the one to two split (basically a “Y” cable) but I can think of a couple of ways to accomplish it with just a little messing around to create a small metal bracket with three cable stops on it (one input and two output).
Perhaps slotting the brake pad material on the rear brake?
In response to the question and answer on the braking for the Paralympic cyclist, one solution would be one lever and 2 pistons of differential size to give different amount of braking power front and back.
Was just reading about the athlete that needs all the controls to his left hand.
I have done this for a customer with similar issues.
Attached [see above] is my latest iteration (Ver 3.0) of all left-hand controls on a Surly Moloko bar on an S-Works Diverge.
I would think if they used an ergo drop bar, with a flat area, it would be possible to mount the Guide brakes in a similar manner as I have done in the pictures.
Because the Guide brakes are all in-line, it is possible to “stack” the brakes and use the index finger for one brake and the middle finger for the other, up to the rider as to which one is which, of course. Using the RSC version, allows for complete tuning of the brakes.
I will deliver the bike this Friday; test riding the bike at the shop, it works much better than I was expecting. My customer will have full control of the bike with one hand. Front brake, rear brake, dropper post and shifting.
— Jeff Ghiselin – Owner
Stray Dog Bicycles
2340 Sunset Blvd #160
Just use a [Shimano] Saint lever. It normally pushes 4 pistons in a single caliper, so pushing 4 in two calipers should be fine. I would do XTR Race calipers, or road calipers, since I think they have the smallest volume.
As a side note, I have seen a guy with no hands and one foot riding double black trails at Whistler (Ride Don’t Slide). He had cups made to insert his forearms, and articulated the brakes with dropping the elbow. Fascinating, and motivating.
I was reading your article regarding the braking system for a Paralympic Cyclist. When Efe spoke about a possible single lever dual disc brake setup, I got to thinking. Has anybody (brake manufacturer) considered a setup where one of the brake lines has an orifice in it to increase the required Force to actuate the piston (F=PxA)? Or perhaps, design a dual brake setup where one of the brake lines has a smaller ID than the other. Then when a single lever setup is used, the lever force would apply a greater force on the larger diameter line assuming that the pistons on both brakes were of the same diameter. If two brake lines of equal diameter were used, perhaps a dial-in-adjust flow restrictor could be designed into the inlet of one of the brake lines to allow for brake modulation setup.
I read your piece today regarding a brake work around for a handicapped rider. I recently completed a similar project for a rider with one arm. The rider in question has only his left hand since birth. We fitted a Shimano Dura-Ace Di2 left shifter programmed to operate the rear derailleur. Front shifting is accomplished by fitting a Shimano climbing switch accessible with the same hand programmed to operate the front mechanism.
The braking was a challenge as my customer wanted hydraulic disc brakes. After much research and consultation with Shimano, SRAM, TRP, and others, we determined that the fluid volume in the master cylinder in the single lever is not sufficient to operate two calipers. Our fix was to use a cable-style lever. A cable runs to a cable doubling device which allows the single input cable to operate two separate cables running to each wheel. We then used TRP’s HY-RD brake calipers, which have hydraulic cylinders on each caliper but are actuated by cables.
The setup works perfectly and the client is very happy with it.
— Justin Karbel
Cos Cob, CT
A potential solution for this special-needs cyclist could be made possible with the Problem Solver cable doubler, if they were willing to use conventional rim brakes or cable discs. I have heard of this being done successfully by a variety of cyclists with special needs.
Could he also mount a rear derailleur fingertip shifter on the left side of his bars?
Regarding the gentleman with the hand strength deficiency, I would strongly recommend against splitting the hydraulic fluid from one lever among two calipers. Any attempt to split the braking force over two brakes will reduce the effectiveness of the front brake, which is the critical brake for maximum deceleration. To quote Sheldon Brown: “The fastest that you can stop any bike of normal wheelbase is to apply the front brake so hard that the rear wheel is just about to lift off the ground. In this situation, the rear wheel cannot contribute to stopping power, since it has no traction.”
A setup with braking force split 50/50 front/rear would lock up the back wheel long before locking up the front wheel, and the stopping distance would be longer than the same bike with only a front brake for someone with limited hand strength.
I would recommend leaving the left brake lever connected to only the front brake, and installing a bar-top lever on the left side connected to the rear brake (purely as a backup in case the front brake fails or the front tire flats). Disc brakes would be a good idea if heat management is a concern, since he won’t be able to easily alternate brakes to give rims a chance to cool.