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I currently have a cheap begginer’s MTB. A Toseek Brandon 27.5er 1x8 with hydraulic disc brakes and I came across a circular drop bar handlebar close to my original flatbar diameter. Is there a possible way to connect my current hydraulic disc brakes to drop bar brake levers?

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  • You just want to keep the pots/calipers and replace everything else? Seems like that should be possible...you'll need to replace the levers though. Jan 17 at 13:07
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This project has numbers of obstacles.

Firstly, drop bar hydraulic levers are hose specific, as are the brakes. In practice you may need to use the same manufacturer for brake lever and the brake. (Never ever mix calipers for DOT fluid with levers for mineral oil or vice versa!) If your brakes are Shimano, the levers should be Shimano. I don't know if Shimano specifies compatibility between "road" levers and "MTB" brake calipers. If not, then you're on your own. They may differ in the amount of fluid pushed per amount of brake lever travel.

Of course you can change the brakes, but do note that "road" brakes usually use flat mount and "MTB" brakes post mount, and if your frame has post mount you probably won't find an adapter for attaching flat mount brakes. If you change the brakes, an option is to use mechanical disc brakes which may or may not be compatible with "road" brake levers. (There is a difference in cable pull ratio: short-pull mechanical disc brakes can only be used with levers made for caliper or cantilever brakes, and long-pull mechanical disc brakes can only be used with levers made for V-brakes.)

Also different calipers and levers may use different size hoses. For example my MTB uses SM-BH59 hose (the calipers being compatible with it) and my road bike uses SM-BH90 hose. Levers made for SM-BH90 hose may not be compatible with SM-BH59 hose.

Also, "road" and "MTB" front derailleurs have different amounts of cable pull. So you need to use friction lever for the front which pretty much limits you to bar-end shifters, unless you want to experiment with pulley wheels that translate the cable pull ratio. If you use bar-end shifters, you probably want to use brake levers that don't have shifters but good luck finding hydraulic Shimano drop bar brake levers without shifters!

Of course it could be an option to change the front derailleur, but do note that "road" front derailleurs don't work with "MTB" triple cranksets because of differing chainline. And also "MTB" chainrings may have so little teeth that a "road" front derailleur would not be optimal. So you may need to replace the crankset as well. Different cranksets may need different bottom brackets (square taper / Octalink: different BBs have different length spindle, Hollowtech II: road and MTB use different bottom bracket cup spacing.) So it's crankset + bottom bracket purchasing time!

Then the rear derailleur cable pull ratio may differ. Shimano 10-speed Tiagra and Shimano 11-speed road use 1.4 as the ratio. MTBs used to use 1.7 as the ratio for 9 speeds and less and shifted to something like 1.2-1.1 for 10-11 speeds (not sure what ratio 12 speeds use). If your bike has 9 speeds or less then great, but if it's a 10 speed (or more) bike, then you won't find levers compatible with the rear derailleur. So you need to swap the rear derailleur.

So, bottom line: doable but expensive. You may need to change brake calipers (mechanical disc brakes being the easiest) and derailleurs plus install new shifters and brake levers, plus possibly new crankset and bottom bracket.

The sitation was very much different when I put drop bars on my 8-speed V-brake hybrid bike I bought in 2008 and swapped to drop bars in 2009. I only needed the handlebar (salved it from a 20+-year old bike I otherwise disposed), 8-speed bar-end shifters (were no longer being manufactured but found some new-old-stock ones from eBay), and Dia Compe drop bar V-brake levers. Plus new inner cables (I reused the old housing). That's it! Nothing else new was needed.

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    Mechanical disk brakes exist for road levers. My CX bike has those.
    – Carel
    Jan 17 at 16:24
  • The hoses are cross compatible (OD stays the same, while the ID is slightly smaller with BH90). All Shimano calipers use the same piston diameter, so that’s also cross-compatible. The front derailleur can work with some limit screw adjustment, but the rear derailleur will be a pain as you mentioned. Finally, 12 speed uses the same “Dyna-Sys” cable pull ratio as 11 speed.
    – MaplePanda
    Jan 17 at 19:26
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    Thanks! Considering buying a road bike instead if the expenses amount that much.
    – Yato
    Jan 19 at 11:03
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I'll keep this short and simple.

Assuming you are using Shimano Hydraulic Disc Brakes, you can use any Hydraulic STI levers as they are known to be compatible with MTB calipers. I recommend Shimano 105 or GRX if you have the money.

You will also need a new rear & front derailleur that is compatible with the road STI levers. Most of which are either 10 or 11 speed which requires you to purchase a new cassette and chain by extension. You could go either 1x or 2x depending on your preference.

Source

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