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I bought a road bike recently and find the road position too uncomfortable for commuting in the city, especially for reaching the brakes fast and slaloming between cars. Therefore, I would like to convert it to a flat bar.

My only issue is with the hydraulic disc brakes (Shimano BR-RS505), is it possible to just replace the levers with other levers ? I understand there is a specific volume of oil that is 'moved' by the lever, but assuming any XC or DH lever has a higher pressing volume, it should work no ? Has anyone gone through such a process ? Is there anything I should be aware of prior to having my brakes undergo surgery ?

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    The better solution would probably be to sell/return the road bike (which seems to be pretty high), and buy a flat-bar road bike/hybrid due to geometry differences (we've covered this ad nauseum if you search for drop bar conversions on this SE). So, unless you're sure switching from drops to flat bar will solve your problem (which may be solvable by changing your riding position / stem / handlebars instead, if you're intent on keeping this bike), I'd recommend you don't do this.+1 for the question of if you can combine Shimano mountain hydraulics with road hydraulic levers or vice versa. – Batman Jan 27 '17 at 20:16
  • A question for the hydraulic brake experts: is there a way to add levers to the tops, like interrupter levers? – Chris H Jan 27 '17 at 20:43
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    Before doing any drastic changes (e.g., flat bars or selling), try changing your fit. There are now a diversity of stem lengths and angles that can be used to alter your fit. Using a stem with more rise will get you in a more upright position, a more upright angle will also will shorten the reach for a given stem length making the brakes easier to reach. Typically set the fit for your most common use position racers that's down low and long, for commuters that's typically shorter and higher. Many shops can assist you with this process. – Rider_X Jan 27 '17 at 20:51
  • @ChrisH only prototypes nothing in production yet. If the fits is right you shouldn't need them, they are a crutch for bad fit. – Rider_X Jan 27 '17 at 20:52
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    @Rider_X you may be right, but if different riding conditions require different positions and you can only have one bike, it can be a lot of effort to change things between rides. – Chris H Jan 29 '17 at 8:33
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The official answer from Shimano as of now is no, as per their road hydraulic systems compatibility chart.

C-499

Someday there may be flatbar road hydraulic levers that make their way onto a new version of that chart, but for now bikes like that just come with conventional MTB/hybrid systems.

There may be combinations that work acceptably, but they will be hacks in an area not a lot of exploration has generally been done in at present.

Matching fluid displacement is not simply a matter of the new lever moving at least as much total fluid as the old one. To perform correctly, the lever has to move fluid at an appropriate rate per distance of lever travel. Hydraulic brakes have a similar version of leverage (aka mechanical advantage) considerations as cable actuated brakes, or at least they would if in practice they weren't mostly black boxes in terms of observing and comparing displacement numbers.

In other words, if you hooked the caliper up to a lever that moved a bunch more fluid, the brake would feel firm and positive at the lever, same as hooking a v-brake lever up to a sidepull, but it wouldn't be generating correct leverage, and stopping power would suffer.

If you go the other direction, less displacement, you get a brake that generates a ton of leverage but the pad movement will be less than what it should be, so it will be prone to issues with the lever bottoming on the bar prematurely, and will feel mushy.

  • Thanks, that's precisely the kind of information I was looking for. Not sure it will deter me from trying though :-) – Stanislasdrg Jan 31 '17 at 9:08
  • Are you aware of an equivalent compatibility chart for SRAM? – SSilk Mar 2 '17 at 3:02
  • @SSilk, what they have is at sram.com/service/include-archived/sram/440 . I don't know if there is a compatibility map document for the HydroR. I believe they say it's a no-go with mountain calipers and vice versa. – Nathan Knutson Mar 2 '17 at 7:51
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Don't do it!!!

I bought a road bike recently and find the road position too uncomfortable for commuting in the city, especially for reaching the brakes fast and slaloming between cars. Therefore, I would like to convert it to a flat bar.

If your brake hoods are positioned correctly, you should be able to commute sitting up with your hands on the hoods, and brake from there. Braking is certainly not as strong from this position, but it's effective enough, and is quicker than getting into the drops to brake.

The problem with a flat bar for commuting, compared to a road bike with drop bars, is that the flat bar is wider. So when you say slaloming between cars, I think you'll be restricted by the extra width.

I have commuted with drop bars this way for 30 years in heavy traffic, and never had a problem with being able to brake hard enough. And that's using traditional cable actuated rim brakes.

If you have not been used to braking from the hoods then it will feel strange at first. Practice, and maybe build up some hand strength in the process. And ride with a little more caution until you gain confidence in your ability to stop. At best, you'll have developed a new skill and saved your money. At worst, you can switch to a flat bar later (with a different bike, because the geometry will be wrong on this one).

Finally, it could be that your brake hoods are positioned too low. They should be set up so that braking is possible from the drops and the hoods.

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    Your answer, however good is a bit opinion based. My benchmark in terms of braking fast is to be able to stoppie, and it's not something I'd be comfortable doing with drop bars even if I had enough braking power. Might sound excessive, but it saved me from hitting a car or a pedestrian quite a few times. – Stanislasdrg Jan 31 '17 at 9:06
  • Wouldn't a 'stoppie', ie using breaking torque on the front to lift the rear wheel, be without effect on the braking distance at best and increase it in all other cases? The only gain you might have is when the stoppie occurs at the very last moment, where you could shave of 2πr (a*/2π) = *ra where a is the maximum angle between your bike and the ground and r the wheel radius. For etrto 622 and π/4 that would be 0.320 m/4 π ≈ 1/4 m. – gschenk Jan 31 '17 at 10:25
  • Yes, it is opinion based :-) We all have to make our own life and death decisions. Being able to do a stoppie is a valuable survival skill. Relying on being able to do a stoppie means you'll be putting yourself in such a survival position repeatedly, and sooner or later the odds will be against you. Using wider flat bars will reduce your options and lower your odds. – andy256 Jan 31 '17 at 10:28
  • @gschenk It means he's braking as quickly as he possibly can, and ending with the rear wheel in the air. The more load on the front wheel, the more grip it has and the harder he can brake, until the rear end lifts. At that point he has to feather the brakes to avoid going A over. But also, with a flat bar, his weight will be higher than it would be in the drops, so his maximal braking will be reduced. – andy256 Jan 31 '17 at 10:30

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