those trying to avoid the cost of hydraulic brifters
by contrast, flat bar brake systems are vastly cheaper
furthermore, the 3-finger brake levers like the Shimano BL-MT200 are even cheaper still because most everyone else wants the higher spec 2-finger brake levers offered at the Deore level & above
preserve the ability to run front triple chainrings
Shimano seems to have entirely dropped support for road triples after Tiagra 4703 series
Shimano seems to have 0 offerings for hydraulic road triple systems
this ecosystem enjoys high discount given that most everyone else has moved onto 1x wide range cassettes
flat bar components are generally cheaper than their equivalent drop bar counterparts
crashes are less concerning for this reason
clutched mountain rear derailleurs, RDs with support for wide range cassettes, etc., are generally more available & cheaper
compare GRX 10 speed versus 11 speed Deore
tightening the mounting bolt is significantly more accessible than Shimano & SRAM brifters, which require partial removal of the hoods for access
this is commonly required when the shifters are knocked out of angle after a crash
Limitations
you need a lot more cable length
for a 51 cm gravel bike, I needed ~1700 mm length to reach with a 120 mm stem
with aerobars, the huge loop going to the rear brake can rattle against your aerobars
front lights probably need to peek through, casting shadows just like with externally routed cables on Shimano 5600, 6600, 7600 shifters
ergonomically difficult/impossible to brake from the drops
brake levers may be hard to reach when in the hoods for those with shorter fingers
this can be partly mitigated by adjusting the reach on brake levers where such a feature is available
bar mitts or pogies are harder to mount
versions exist to accommodate externally routed cables which exit toward the midplane of the bike, not like this
Safety
safety is a considerable concern with this particular 3DP part
the part sees a large clamping load in order to avoid slipping on the handlebar
riding scenarios like riding off curbs, jumps, & sprinting could all cause crashes
ISO 4210 doesn't appear to govern the lever bodies themselves, but does pose these scenarios which serve as a first order approximation of our scenarios
Brake lever actuation force
180 N = 41 lbf
Load on drop bars at hood position
Cyclical loading considered here – fully reversed loads
Validation of safety
I did seriously consider rigging up test fixtures, hammering on the 3DP parts to generate qualitative data, but ultimately decided against it, mostly out of laziness
instead, I decided to test printed hoods on my own bike & simply ride around; at first cautiously, but later somewhat aggressively
Material
most brifter bodies are injection molded from nylon with glass fiber fill which is an incredibly tough & stiff material well suited & proven for the task
therefore, plastic fundamentally is adequate
some hydraulic brifter bodies are cast metal, but I believe MFRs have moved away from this in favor of weight & cost savings once PA-GF was validated
caveat that there exist many types of PA & I don't know which particular breed is used in brifter bodies
ultimately, I settled on MarkForge Onyx filament, a pricey but mechanically stellar nylon with chopped CF
continuous fiber reinforcement would probably be ideal, but I had no such access
it is possible that other PA-CF & similar filaments could suffice
I also considered Formlabs Tough 2k & Tough 1500 resins, but never tested due to fears of brittle failure
I'm not familiar with SLS enough to comment on their suitability
to maximize strength & lessen the gamble on my life & injury to other road users, I printed with 100% infill
Part breakdown
printed parts
qty 1 hood
printed out of Flexible 80A resin from Formlabs on a Form 3
qty 1 body
print at 100% infill, PA-CF preferred
only MarkForged Onyx filament validated
print qty 2 – no mirroring necessary for recent revisions, around R24
hardware
M6 x 55 mm CSK
I generally prefer CSK hardware due to the large clamping area to reduce stress, but with certain print orientations, the CSK head can split FDM layers apart, so be careful
Shimano band clamp with captive M6 thread
note the permanently attached square nut
note the Shimano branding
the ones that come with Tektro RL340 brake levers are not compatible
the ones on newer Shimano brifters (since roughly 5600/6600/7600 generation) are not compatible
Design
Ensuring sufficient brake lever pull
bottoming out the lever against anything is a big risk – if it happens, you wouldn't be able to brake any harder
consequently, the 22.2 mm fake “flat bar” must be proud
this complicated the mounting of that bar, especially when it used to be a separate metal handlebar segment clamped
here is a test that validated on a Shimano Tiagra brake lever, that even at full load & with the reach dialed as close to the bars as possible, there is still a healthy clearance
this test was repeated with hydraulic brake levers (Shimano BL-MT200)
Blending with drop bar
I vastly prefer the ergonomics of installing brake levers such that the hoods are level & flat relative to the tops of drop bars, like in this picture
this is in contrast to older installations, which look more like this
I started by trying to SWEPT CUT some generic compact drop bar shape
but ultimately decided to make it more like commercial road brake levers, which protrude surfaces deliberately to bear the compressive preload of the mounting bolt
this way, the contact with the drop bar is not ambiguous & possibly less likely to slip, even though the surface area contact is much reduced (it's impossible to predict this well for any given drop bar)
note the band of material above the clamp protrudes to bear the load
a tiny bit of clearance is needed above, but is again hard to predict – too much of a gap will be compatible with many drop bars, but fail to support the hand when bridging the valley created between the bar & the hood body
Maintenance of this project
the limitations of the product, even if more completely developed, would still exist – namely being unable to brake from the drops
as such, I am henceforth abandoning this project & will no longer maintain or update files
Known things to fix
hoods need trimming in CAD at the bottom where they meet the handlebar to mitigate splitting/cracking which still happens with Flexible 80A resin – I fixed this in the model but didn't print to validate the fix
see the non drive side control in this picture, as compared to the drive side control
the outside corners are very unergonomic & have little reason to be there
Common failures
lever body easily slips relative to bar, like this
body not sufficiently tight against drop bar
interestingly, I could not torque the M6 bolt above ~9 Nm without slippage
the M6 female thread on the band clamps seemed entirely intact & certainly not freely spinning
it's almost as if the plastic was yielding such that further load was plowing material out of the way & relieving the stress such that additional torque couldn't be achieved at the bolt
at this torque, the hex socket drive started to strip & round out in multiple instances/bolts