The RMU Nighttrain uses a dual-idler suspension design, which looks like a great way to handle bumps. However, a demo bike showed 6-8mm of chain movement. RMU stated that adjustment can resolve the chain slack, but it makes me think about the long-term upkeep for these setups.
For those of us who prefer mechanical simplicity, adding idlers introduces more moving parts to keep in check. I am interested in how this affects the usual routine for keeping a drivetrain crisp and silent.
What specific drivetrain maintenance and tension checks are necessary for bikes using dual-idler suspension systems?
You're basically adding two more points of friction and wear to the mix. Beyond the usual chain lube, you'll need to check the idler bearings for grit or play regularly; if they get crunchy, your whole drivetrain will feel sluggish regardless of how well the derailleur is tuned. The big one is checking for pulley alignment. If those idlers aren't perfectly parallel, you'll get that same annoying rub you usually fight with a front derailleur. Just keep a close eye on the bolt torque for the idler mounts so they don't shift under load, and you'll be fine. Understanding these little points is what makes you a more confident rider anyway.
Just keep a close eye on the bolt torque for the idler mounts so they don't shift under load, and you'll be fine.
Bolt torque is only half the story – after you tighten the mounts you must re‑check the chain tension. The extra idlers change the effective wrap, so I always run a tension gauge (or the half‑turn method) and fine‑tune the rear axle until the chain sits snug but not tight. A loose chain will bounce on those 6‑8 mm of movement the Nighttrain demo showed, and a tight chain will stress the links on steep climbs.
And speaking of steep climbs – shifting under maximum torque is the number one cause of snapped chains. I make a habit of easing the pedal pressure for half a stroke before any upshift on a hard climb; it saves the chain and the peace of mind.
So, in addition to checking idler bearings for grit and keeping the pulleys parallel, add a post‑adjustment chain‑tension check and avoid shifting under full load.
I make a habit of easing the pedal pressure for half a stroke before any upshift on a hard climb; it saves the chain and the peace of mind.
That is a bit precious for actual trail riding. If you are mid-climb on a technical section, you cannot always afford to lose momentum or dance around your pedal stroke just to pamper the chain. Modern drivetrains are built to handle a decent amount of torque; as long as you aren't absolutely hammering a dead-stop shift, you aren't going to snap a chain every time you upshift under load. I'm more concerned with keeping the idler bearings clean and the pulleys aligned so the chain actually tracks straight, rather than obsessing over half-strokes.
Modern gear can take a lot, but that is a gamble you do not need to take. A clutch derailleur and a clean 1x setup are great, but shifting under max load is still the fastest way to chew through a chain or bend a link. I will take a half-stroke of easing over a snapped chain and a long walk back from the trailhead any day.
Besides, once you start adding dual idlers and complex linkage just to manage chain growth, you are already deep in the weeds with maintenance. I'll stick to my hardtail; no idlers to align, no bearings to get crunchy, and a drivetrain that actually stays simple.
Besides, once you start adding dual idlers and complex linkage just to manage chain growth, you are already deep in the weeds with maintenance.
That is a bit of an exaggeration. Whether you have idlers or a simple hardtail, the real secret to a crisp drivetrain is just a disciplined cleaning routine. A spotless chain and well-lubricated links save more watts and protect your cassette far better than worrying about how many pulleys are in the mix. If you keep the grit off, those idler bearings won't magically turn into pumpkins overnight.
