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It's not clear to me if the disc/disc valves do any proportioning. I'm guessing not, but it probably gives you the safety valve and warning light switch. I may be way off, but I've never seen any specs on what kind of bias they use. I guess I haven't seen that for a disc/drum valve either though. You would think that requirement would vary a lot based on front to rear caliper piston size, weight dist, etc. I was going to plumb mine without any kind of valve but now I've about talked myself into the adjustable setup.