It's an interesting observation but I think once you account for lever positioning (in use) many reservoirs or at least the intake/return port are below the bore (in usage). Maybe less so now that everyone seems to be [**French**](https://www.youtube.com/watch?v=7YHDpunS4yQ). As you say, Hayes has always been this way.
I've never heard of it being an issue with Hayes but I know some older Magura brakes really didn't like to be run in a more perpendicular position especially with the pads near end of life. That could also come down to reservoir size.
What Jeff noted that Hayes has always done but other bike companies don't do is the multiple intake/return ports which are more common in other applications for which Hayes manufactures brake systems.
...
This is stretching/extrapolating my first-hand knowledge (I'm not a mountain bike historian - and I'm always ready to be corrected/enlightened) but looking at the first hydraulic disc braking systems on the bicycle market with the exception of Hayes they were derived from brakes for mopeds. In that statement, I'm including Magura (Gustav), Formula, and Grimeca - Italian companies making moped brakes - and also Shimano and SRAM (not Avid) whose systems had way too much in common with Grimeca brakes to be a coincidence. Hope also had interchangeability with Grimeca - pads for sure and I can't recall for certain if there were other parts - and Formula manufactured the first Avid Juicy brakes.
On the other hand, Hayes has long make brakes for heavy industrial equipment with a sideline doing systems for Harley Davidson motorcycles so I'd say while the basic principles of hydraulic brakes are the same they were maybe coming at it from a different space than other companies that could/did largely adapt existing products.
Nov. 10, 2019, 7:36 p.m. - Andrew Major
It's an interesting observation but I think once you account for lever positioning (in use) many reservoirs or at least the intake/return port are below the bore (in usage). Maybe less so now that everyone seems to be [**French**](https://www.youtube.com/watch?v=7YHDpunS4yQ). As you say, Hayes has always been this way. I've never heard of it being an issue with Hayes but I know some older Magura brakes really didn't like to be run in a more perpendicular position especially with the pads near end of life. That could also come down to reservoir size. What Jeff noted that Hayes has always done but other bike companies don't do is the multiple intake/return ports which are more common in other applications for which Hayes manufactures brake systems. ... This is stretching/extrapolating my first-hand knowledge (I'm not a mountain bike historian - and I'm always ready to be corrected/enlightened) but looking at the first hydraulic disc braking systems on the bicycle market with the exception of Hayes they were derived from brakes for mopeds. In that statement, I'm including Magura (Gustav), Formula, and Grimeca - Italian companies making moped brakes - and also Shimano and SRAM (not Avid) whose systems had way too much in common with Grimeca brakes to be a coincidence. Hope also had interchangeability with Grimeca - pads for sure and I can't recall for certain if there were other parts - and Formula manufactured the first Avid Juicy brakes. On the other hand, Hayes has long make brakes for heavy industrial equipment with a sideline doing systems for Harley Davidson motorcycles so I'd say while the basic principles of hydraulic brakes are the same they were maybe coming at it from a different space than other companies that could/did largely adapt existing products.