I'm going to document my plan since I seem to have too much time on my hands these days. I will preface this with I am an engineer and I've been designing dampers since 2013 so I'm really good at pretending to know what I'm doing.
I have a habit of designing parts for cars I own and the awesome new2me F30 I recently picked up is no exception. I may make some separate threads to document the other things but for now I'm going to take the cheapest route to a great custom rebuildable coilover system.
Cheap
First I decided not to design and manufacture every single thing, way too expensive and there is no point in reinventing the wheel when it comes to structural bits. I only care about improving the hydraulics. So I shopped around for a cheap rebuildable monotube design that ideally would be easy to get parts for instead of the whole assembly. The best I could come up with is BC's offering which turns out is pretty spectacular for what I'm going to do. Their website lets you buy almost every part of their damper as individual components and their main tube ID finish is more than acceptable.
Ideally I would buy the main tube without everything in it but that is their business' main component, most likely shipped from Taiwan fully assembled so that's never going to happen. That means in the short term I can take the hydraulic assembly and just replace the main piston, the adjuster, and the oil and be happy. Medium term I could swap out the rod guide and floating piston to reduce friction. Long term I could add a remote can for more travel, adjustability, and lower gas pressure for a further reduction in rod force and friction.
I think I have everything I need in the shopping cart at $575.
Rebuildable
I need to make some custom tooling and dyno mounts but BC shocks can be fully disassembled. Perfect.
Specification
BC comes with a single main piston bleed adjuster. It adjusts compression and rebound at the same time which is just flat out unacceptable. The adjuster range and linearity between clicks also leaves me wanting more.
3in/s 16 clicks which is middle of the adjustment range. I'd like to get hysteresis down a bit here.
And of course "dyno tested" out of Taiwan doesn't mean much. There is an issue with the adjuster when its fully closed. Probably too far off on the length of the metering rod but I need to dig in and double check my design length vs. theirs vs. each of the shaft's variation in length.
Force velocity - full stiff 3in/s
Force displacement - full stiff 3in/s
Step 1: Swap out the needle jet for one that checks compression flow so the adjuster only works on rebound bleed. I can design this the opposite way to make it a compression bleed adjuster, perhaps to speed up the tuning process. In order to integrate a dual bleed adjuster I'd need to make a new shock shaft and all the guts which isn't worth it right now. Also, swap out the floating piston cause that's easy.
Progress - Done.
Step 2: A little more difficult. They've integrated the needle and the rod pushing the needle from the external adjuster into one long piece. More investigation is required but it may take machining the ID of the main shaft to get what I want out of the needle diameter and profile.
Progress - Currently measuring critical features and will reuse a needle profile I previously developed.
Step 3: Design a new high flow and double digressive main piston to my liking. RE Suspension sells shims I'll design around. Already have the high flow I just need to tweak for their bore and rod tennon.
Step 4 Buy some hyperco springs, build, install, and tune. Then maybe make the double digressive piston and start looking at integrating a piggyback.
Some other fun bits I'm working on this year are below. I haven't decided yet but I may go full send and change everything to a centerlock style.
