Flat bar extensions for bullhorn handlebars

Motivation

• ebikes generally have a bunch of things mounted to the handlebars, which are typically flat unless it's an electric road bike

• these often include

  • brake levers

  • shifters

  • controller

  • computer

  • throttle

  • front light

• the easiest way to accommodate this is a very wide handlebar

• this is unfriendly due the clearances required to fit between cars in traffic

• bullhorn bars, on the other hand, are much less wide

  • as an added bonus, they feature a lot of reach, to counteract the short reach inherent in a lot of ebike frames

How to make bullhorn bars work

• short stem to compensate for extreme reach

• bullhorn bars feature a 23.8 mm OD, same as drop bars

• flat bar components mount to 22.2 mm OD, so an adapter is required

Design

• designed to mount approximately these items

  • Bengal Ares hydraulic brake lever

  • SRAM GX 10 speed shifter

  • Aventon controller

  • Aventon throttle

  • Lezyne front light

Rev 1

Hardware for single adapter

• qty 1 M6 x 100 mm button head screw

  • 4 mm drive

• expansion mechanism from Tektro RX 4.1 bullhorn brake levers

  • I did consider using a custom 3DP mechanism like a quill stem, but decided against it for these reasons

    • to expedite testing for feasibility

    • strength, since this will be the foundation for a brake lever

    • strength despite relatively small overlap with the handlebar

      • many bullhorn bars feature a curve at the end, which complicates insertion beyond a certain depth

        

Installation

• apply grease to the wedge & the mating threads to facilitate later removal

Limitations

many of these are the same as with my other project here, the control hoods.

• you need a ton of extra cable length to make this work

  • this is challenging for

    • internally routed hydraulic cables

    • existing electrical connections for brakes, the controller, computer, etc.

  

Note the kinked rear brake hose

Nearly kinked front brake hose

Rev 2

• features a straight rather than a curved grip, but neither have been tested to date (2025-01-18)

Future improvements

• I thought about integrating TPU grips, but decided against it to avoid scope creep

• chances are slip on grips like ESI grips would suffice

  • due to the curvature at the very end of most bullhorn bars, lock on grips will not work

  

• the only way I can proceed with this project as is, is to address the cable length issue, which I might if Bengal Ares brakes can use standard Shimano BH59 hoses

  • otherwise, something like this would greatly reduce the cable length requirements